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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.
111

Vývoj kompozitního materiálového systému se zaměřením na matrici pro extrémní podmínky / The development of composite material system with focus on matrix for extreme conditions

Gratclová, Kamila January 2016 (has links)
The thesis deals with composite systems, with a focus on matrix resistant to extreme conditions. The aim of this work was to research and development matrix, resistant to high temperatures, typical in case of fire. Used theoretical knowledge were realized with subsequent laboratory research. Attention was paid matrices based binder mixed with any alkali activation of alternative raw materials and geopolymers. Scattered reinforcement featured polypropylene fibers. The subject of the practical part of the two alternatives, including a matrix based on basic ingredients - cement, alternative raw materials - high fly ash, blast furnace slag, geopolymer and polymeric components incl. combinations thereof. Laboratory research conducted by determining the fundamental material properties such as density, strengths, etc., after heat exposure. The developed materials were subjected to a temperature 1400 ° C. The conclusion was selected several recipes that were based on the resulting values found to be optimal.
112

Développement d'une stratégie de regroupement dynamique d'actions de maintenance pour un système de production géographiquement dispersé / Development of a dynamic grouping maintenance strategy for a geographically dispersed production system

Nguyen, Ho Si Hung 10 September 2019 (has links)
Ces dernières années, un nouveau type de système de production nommé système de production géographiquement dispersé (GDPS) est prôné par de nombreuses entreprises manufacturières internationales. Par cette vision « dispersée », il présente un certain nombre d'avantages tels que l'économie des coûts du produit livré (puisque proche des clients), l'amélioration de la qualité des services (délais de livraison courts, services après-vente de haute qualité) favorisant la pérennité et la compétitivité des entreprises dans un contexte de compétition mondiale. Cependant l’exploitation multi-sites d’un GPDS est confronté à de nombreux défis concernant les normes, les réglementations, la maîtrise des flux de production, et en particulier la planification et l'optimisation de la maintenance en raison de la dispersion géographique des sites de production. Sur ce dernier point et plus globalement la définition d’une stratégie de maintenance adaptée au GDPS, peu d'études ont été menées compte tenu de la jeunesse du sujet et de la complexité des GDPSs (ex. multi-sites, multi-composants). Cette thèse se positionne donc sur ce sujet émergeant avec comme objectif de développer une stratégie de maintenance de regroupement dynamique pour un GDPS en tenant compte de dépendances à la fois aux niveaux composants et sites de production (dépendances économique et géographique) et des impacts des contextes dynamiques (à savoir, taux de détérioration variable des composants, modification des itinéraires de maintenance, possibilités de maintenance, etc.) auxquels il est soumis. Dans cette stratégie, les itinéraires de maintenance et l'ordonnancement sont considérés conjointement dans un modèle global. Le modèle vise à trouver un plan optimal de maintenance et de routage des ressources de maintenance. A cette fin, une structure de coûts et un modèle de dépendance qui prend en compte conjointement la dépendance économique et géographique sont formulés. Ils servent de base à l'élaboration du modèle global de planification et d'ordonnancement de la maintenance et du routage. De plus, pour la recherche de la solution optimale, des algorithmes d’optimisation basés sur l'algorithme génétique et l'algorithme Branch and Bound sont proposés. Enfin, une étude numérique est investiguée pour évaluer la performance, les avantages et aussi les limites de la stratégie proposée. / In the recent years, the Geographically Dispersed Production System (GDPS) with a number of advantages such as saving the product delivered costs (closed to the clients), improving quality of services (short delivery time, high quality after-sales services) has been extensively developed by many manufacturing companies to ensure their competitiveness. In operation, the GPDS faces many challenges concerning standards, regulation, production management, and especially maintenance planning and optimization due to the geographical dispersion of production sites. However, few studies have been developed for maintenance strategies of GDPSs. To face this challenge, the main objective of this thesis is to develop a dynamic grouping maintenance strategy for a GDPS with consideration of dependencies between at both component and site level (economic, geographical dependencies) and impacts of dynamic contexts (i.e. varying deterioration rate of components, change of maintenance routes, maintenance opportunities, etc.). In this strategy, maintenance routing and scheduling are jointly considered in a global model. The model aims at finding an optimal maintenance and routing plan. For this purpose, a cost structure and a dependence model jointly considering economic and geographical dependence are formulated. They are used as a basis for the development of the global model of maintenance routing and scheduling. In addition, to find a joint optimal maintenance and routing plan, advanced algorithms using jointly Genetic Algorithm and Branch and Bound are proposed. Finally, a numerical study is investigated to evaluate the performance and the advantage as well as limits of the proposed maintenance strategy.
113

Infrared Transition Moment Orientational Analysis on polymeric systems

Kossack, Wilhelm 28 October 2015 (has links)
In dieser Arbeit wird ein Verfahren entwickelt (Infrared Transition Moment Orientational Analysis, IR-TMOA) um die dreidimensionale Ordnung auf molekularer Ebene in infrarot-durchlässigen Systemen zu quantifizieren. Es beruht auf der Messung zahlreicher Infrarotspektren, die unter systematisch variierender Polarisation des einfallenden Lichts und Ausrichtung der Probe relativ zur optischen Achse aufgenommen werden. So wird ein repräsentativer Ausschnitt des dreidimensionalen Absorptionsellipsoids gemessen. Die Tensordarstellung dieses Ellipsoids ist äquivalent zum quadratischen Mittel der Verteilungsfunktion der Orientierung der Übergangsmomente, was wiederum dem Ordnungsparameter entspricht. Von zentraler Bedeutung ist ebenfalls, dass die Ordnung (und Orientierung) spezifisch für verschiedene molekulare Untereinheiten angegeben werden kann, da im mittleren Infrarot die Übergangsdipolmomente definierten, lokalen Schwingungen zugeordnet sind. Im zweiten Teil der Arbeit wird IR-TMOA angewendet um die molekulare Ordnung von verschiedenen amorphen und kristallinen Untereinheiten in teil-kristallinen Polymeren (Polycaprolacton, PCL und Polyethylen, PE) zu bestimmen. So kann der Einfluss der Grenzflächen und der geometrischen Einschränkungen in PCL-Filmen auf Substraten in seiner Temperaturabhängigkeit charakterisiert werden. Ebenso wird erstmalig in freitragenden PCL-Filmen in durch mechanische Streckung plastisch deformierten Bereichen die stark biaxiale molekulare Ordnung quantifiziert. In industriell produzierten PE-Filmen, die unter dem Einfluss von äußerer mechanischer Spannung kristallisieren, wird die biaxiale Ordnung und Orientierung vollständig charakterisiert und in Abhängigkeit der Präparationsbedingungen analysiert. Des weiteren wird die Ordnung in einem System aus zwei Phasen untersucht: einer ferroelektrischen Polymermatrix mit mikrometer-großen Flüssigkristalleinschlüssen (Polymer Dispersed Liquid Crystals). Dies erlaubt es, den Einfluss eines äußeren elektrischen Feldes und des remanenten Feldes der Matrix auf die Flüssigkristalle zu quantifizieren. Durch IR-TMOA wird für alle Systeme, die infrarot aktive Vibrationen aufweisen, eine dreidimensionale molekulare Beschreibung der Orientierung und Ordnung ermöglicht. Dies stellt wiederum einen unverzichtbaren Beitrag zum Verständnis der unterliegenden strukturbildenden Prozesse dar und deren Beitrag zur resultierenden makroskopischen Struktur.
114

Особенности структурно-механических свойств нефтяных дисперсных систем

Boytsova, Alexandra 18 February 2019 (has links)
The present-day challenge of oil industry is gradual decrease of conventional light crude reserves and increased consumption of hard-to-recover heavy crude. The goal of thesis is to establish change regularities of structural-mechanical properties and thermody-namic activation parameters for viscous flow in oil dispersed systems (ODS) of various composition (paraffin and naph-thene and aromatic bases) from Timan-Pechora petroleum region (Russia) in a broad range of temperatures and shear rates and under the exposure of external fields, and also to experimentally determine phase diagrams of binary hydrocarbon systems (nonadecane – decaline and nonadecane – naphthalene) modeling ODS mixture of completely opposite nature. Study results can be used for predicting and preventing structure formation during production, transport and storage of ODS's with various content of solid paraffins, resins and asphaltenes.:INTRODUCTION CHAPTER 1. ANALYSIS OF THE MODERN CONDITION AND METHODS OF RESEARCH OF HEAVY OILS 1.1 The current state of hydrocarbon reserves 1.2 Oil classification 1.3 Oil chemical composition 1.4 Influence of components of oil dispersed systems on their low-temperature properties 1.5 Structuring in oil dispersed systems 1.6 Rheological models of oil dispersed systems 1.7 Evaluation of the thermodynamic characteristics of the activation of the viscous flow of oil dispersed systems 1.8 Chemical composition and structural-mechanical properties of the oils from Timan-Pechora province 1.9 Modern methods of influencing the structure and properties of oil dispersed systems CONCLUSIONS TO CHAPTER 1 CHAPTER 2. OBJECTS AND METHODS OF RESEARCH 2.1 Objects of research 2.1.1 Physical and chemical properties of oils from Timan-Pechora province 2.1.2 Physical and chemical properties of high-boiling fractions from Timan-Pechora province 2.1.3 Physical and chemical properties of light distillate from heavy oil and individual hydrocarbons (nonadecane, decaline and naphthalene) 2.2 Research methods 2.2.1 Methods of conducting research on the physicochemical properties of oils 2.2.2 Methods of determining the group hydrocarbon composition of oil dispersed systems 2.2.3 Method for determination of low-temperature properties of binary systems 2.2.4 Methods for determining the structural and mechanical properties of oil dispersed systems from Timan-Pechora province 2.2.5 Characteristics of sources of external impact on oil 2.2.6. Methods of processing samples by external influence CONCLUSIONS TO CHAPTER 2 CHAPTER 3. INVESTIGATION OF LOW-TEMPERATURE PROPERTIES OF BINARY AND OIL DISPERSED SYSTEMS 3.1 Justification of the computational models used to describe the phase diagrams of binary systems 3.2 Investigation of low-temperature properties on model binary systems of nonadecane-decaline and nonadecane-naphthalene 3.3 Investigation of the low-temperature properties of a light distillate mixture (NK-330 °C) of heavy naphthenic-aromatic Yarega oil and light paraffin haryaga oil CONCLUSIONS TO CHAPTER 3 CHAPTER 4. INVESTIGATION OF CHANGES IN STRUCTURAL AND MECHANICAL PROPERTIES OF OILS AND THEIR HIGH-BOILING FRACTIONS UNDER EXTERNAL EXPOSURE 4.1 Determination of the type of liquid in oil dispersed systems at different temperatures 4.2 Determination of the dependence of the ultimate shear stress of oil dispersed systems on temperature 4.3 Investigation of the thixotropic properties of the oils from Timan-Pechora province 4.4 Impact of external fields on the rheological properties of heavy oil 4.5 Effects of external fields and diluents on the rheological properties of heavy oil CONCLUSIONS TO CHAPTER 4 CHAPTER 5. RESEARCH OF THERMODYNAMIC CHARACTERISTICS OF THE ACTIVATION OF A VISCOUS FLOW OF OILS AND HIGH-BOILING FRACTIONS UNDER DIFFERENT CONDITIONS (TEMPERATURES AND SHEAR RATE) 5.1 Liquidus temperature and activation energy of viscous flow of oil dispersed systems 5.2 Thermodynamic characteristics of the activation of a viscous flow of oil dispersed systems 5.3 Investigations of the strength of intermolecular interaction in oil dispersed systems as a function of the frequency of molecule jumps 5.4 Change in the activation energy of viscous flow of oil dispersed systems with increasing shear rate 5.5 Changes in thermodynamic characteristics of the activation of a viscous flow of oil dispersed systems with increasing shear rate 5.6 Changes in the strength of intermolecular interaction in oil dispersed systems with increasing shear rate CONCLUSIONS TO CHAPTER 5 CONCLUSION LIST OF ACCEPTED REDUCTIONS BIBLIOGRAPHY ANNEX 1. Act of introduction of development in LLC LUKOIL-Ukhtaneftepererabotka APPENDIX 2. Patent of the Russian Federation 'Method of preparation of heavy oil for refining
115

Studium vlivu organických vláken na požární odolnost betonu / Study of the influence organic fibres on the fire resistance of concrete

Klobása, Jan January 2022 (has links)
The master thesis is focused on current issues of concrete behaviour under high temperatures. In the theoretical part, a search of knowledge about changes in concrete, which take place when exposed to thermal loads, which simulates the effect of fire, is performed, and summarized. It is also important to summarize the changes in the individual components that are used to produce concrete. This work describes the effect of high temperatures on mechanical and physical properties as well. There is an information about the most used fibres and their function in concrete. Emphasis is placed on describing the possibility of using recycled PET or cellulose fibres due to the positive environmental impact. In the experimental part, recipes with different types and amounts of fibres are proposed. The subject of the research was to determine how individual types and amounts of fibres affect the physical mechanical properties of concrete and their suitability for use at high temperatures. Microscopic scanning and study of changes in the structure of concrete was also performed.
116

Teaming at a Distance: The Work Experience on Global Virtual Teams

Maley, Lejla Bilal 01 May 2020 (has links)
No description available.
117

A Place of Passage : Disturbed burials and dispersed human bone remains from the Mid-Neolithic burial ground at Ajvide on Gotland / Övergångsplats : (För)störda begravningar och spridda mänskliga skelettrester från det mellanneolitiska gravfältet i Ajvide på Gotland

Sointula, Anna January 2023 (has links)
The Mid-Neolithic site of Ajvide on the Baltic Island of Gotland comprises the burials of 89 individuals within 85 separate burial contexts (Österholm 2008). Some of these individuals were detected with absent skeletal elements, such as the cranium, which have been believed to be represented by the considerable number of dispersed human bone fragments discovered from the site (Burenhult 2002: 33, see also Lundén 2012). These occurrences were initially proposed to be caused by agricultural ploughing, which however has not been done on the fields of Ajvide with the modern machinery of the late 20th century (Burenhult 2002: 31). It was hence the intention of this study to investigate the alternative motives behind these phenomena, by reviewing the statistics between these skeletal materials. The correspondence was additionally analysed with some other selected variables on the available data from these burial contexts. Based on the attained results, it was concluded that the human skeletal remains from the disturbed burials were likely intentionally retrieved to be used in the different ritual activities of the PWC populations on Gotland. / Den mellanneolitiska Ajvidelokalen på Gotland omfattar 85 begravningar av totalt 89 individer (Österholm 2008, Burenhult 2002). Vissa av individerna påträffades utan specifika skelettelement, såsom kraniet. Dessa individer har använts som representanter för tolkningen av den markanta kvantiteten av spridda mänskliga benfragment, som hittats via arkeologiska utgrävningar på lokalen (Burenhult 2002: 33, se även Lundén 2012 och Wallin 2015). Till en början ansågs jordbruksplogningen vara ansvarig för detta fenomen, dock har inga plöjningar utförts med moderna maskiner, eller sedan 1900-talet (Burenhult 2002: 31). Därmed, var syftet med studie att undersöka alternativa tolkningar bakom dessa fenomen. Studien är på analyser av de två olika grupperna med skelettmaterial, som inkluderats i en statistisk modell. Dessutom utfördes en korrespondensanalys mellan andra särskilt utvalda variabler från varje gravkontext. Studien har konkluderat, att de mänskliga skelettresterna från de förstörda begravningarna, hämtades sannolikt avsiktligen för olika rituella aktiviteter som praktiserades av den mellanneolitiska befolkningen på Gotland.
118

Fault energy implications of distributed converter interfaced generation : A case study of an underground mine grid / Distribuerad omformardriven generering och dess påverkan på kortslutningsenergi : En fallstude i ett gruvkraftnät

Hjertberg, Tommy January 2021 (has links)
Adding Power Electronic Interfaced Devices (PEID) generation to grids is an increasing trend because of the concurrent development of better power electronic converters and a greater interest in a better utilisation of energy resources. Small and dispersed energy sources that would previously not be worth introducing into the grid is becoming more and more viable and other potential benefits such as better control of voltage levels and smoothing out load changes also spur this development. But while there are great potential benefits of the controllability of these devices there are also risks when existing protection systems are made for the linear behaviour of traditional synchronous generators. This thesis describes the peculiarities of the short circuit behaviour of PEID generators and how this affects the short circuit energy levels in terms of short circuit current, I2t and incident arc energy. Using simulation, it is shown that in the case of the specific mine grid studied, the incident arc energy increases substantially and that this need to be considered when evaluating installation of PEID generation. / Användningen av nätansluten omformardriven generering ökar alltmer i takt med att bättre omformare utvecklas och intresset för ett effektivare nyttjande av energiresurser ökar. Små och utspridda energiresurser som tidigare inte var värda att ta vara på tillgängliggörs alltmer, och fördelar som bättre spänningsreglering och lastutjämning driver på utvecklingen. Men med de fördelar som kommer av omformarnas reglerbarhet så kommer också risker beroende av deras olinjäritet, eftersom existerande skyddssystem är anpassade till det linjära beteendet hos traditionella synkrongeneratorer. Den här avhandlingen behandlar säregenheterna i kortslutningsbeteendet hos effektelektroniska omformare och hur det påverkar kortslutningsenergin i bemärkelsen I2t, händelseenergin vid ljusbågar samt kortslutningsströmmen. Via dynamisk simulering så visas att händelseenergin i vissa fall kan öka avsevärt och att detta behöver övervägas vid installation av omformardriven generering.
119

Développement d’un code numérique pour la simulation et l’étude de l’hydrodynamique et de la physico-chimie de milieux diphasiques incompressibles. Cas d’une goutte d’eau dans l’huile de paraffine / Development of a numerical code for the simulation and study of the hydrodynamics and the physical chemistry of incompressible two-phase media. Case of a droplet of water in paraffin oil

Fanzar, Abdelaziz 25 September 2014 (has links)
Depuis plusieurs décennies, une importante activité scientifique se concentre sur la description numérique, théorique ou expérimentale de l'hydrodynamique des écoulements multiphasiques. Ces écoulements sont caractérisés par l'existence d'interfaces, et d'une force à l'interface, la tension superficielle, séparant généralement deux fluides non miscibles. Un cas d'étude dans ce contexte est le problème du drainage d'une unique goutte dans une phase continue, l'ensemble étant soumis à la gravité. Ce système fait apparaître des écoulements récemment décrits pour une goutte d'eau dans l'huile de paraffine. Ce système constitue également un modèle simple pour l'étude des propriétés aux interfaces, Mais d'un point de vue numérique, se pose alors le problème de la stabilité des algorithmes pouvant être utilisés. Les effets aux interfaces impliquent en effet des domaines spatiaux très limités dans lesquels les grandeurs physiques entre les deux fluides sont discontinues. D'importants artéfacts numériques peuvent alors être générés dans les simulations et faire perdre la richesse de la physico-chimie du système considéré. Le problème de la simulation d'écoulements multiphasiques intéresse aussi bien le monde académique que le monde industriel. L'objectif de ce travail de thèse est donc d'implémenter les techniques numériques les plus récentes et de développer un code pour permettre la simulation de l'hydrodynamique de systèmes dispersés. Pour parvenir à ce but, il reste encore des problèmes algorithmiques importants à résoudre comme la prise en compte des effets thermocapillaires et thermosolutaux. Ces deux derniers points sont l'objet de cette thèse. / For several decades, an important scientific activity has focused on the numerical, theoretical and experimental hydrodynamics of drops. This work presents numerical results of a single droplet in the gravity field and in non-isothermal conditions. The simulation such a multiphase system is important in both academic and industrial world. This is particularly the case in the field of emulsions, wetting problems and evaporation. To achieve this goal, there are still important algorithmic problems due to the free moving interfaces and the description of capillary effects. Here, a Volume of Fluid technique has been implemented with high order temporal and spatial schemes to preserve the sharpness of the drop interface. The system under consideration is a simplified model consisting in a single water droplet in a continuous paraffin oil phase. These liquids are immiscible and non-compressible and the overall evolution is unsteady. Capillary contributions such as temperature and surfactant dependent surface tension are fully accounted for. This presentation is aimed to show the capabilities of VOF techniques for the simulations of unsteady multiphase systems in non-isothermal configurations. The role of the droplet initial position and temperature field is described with good numerical stability. There are still important problems remaining in the simulation of free interface systems with such a technique. Spurious currents induced by the description of capillarity can in particular come into play. But these latter can be controlled once the droplet average velocity due to drainage becomes large enough.
120

Modelagem e análise das cadeias de suprimentos globais e resilientes baseadas em rede de Petri. / Modeling and analysis of global and resilient supply chain based on Petri Net.

Kano, Célia Hanako 16 June 2015 (has links)
Em um cenário de aumento de competitividade, crescente expectativa por inovações do produto e necessidade de atender diferentes perfis de consumidores, o conceito de gerenciamento de cadeias de suprimentos globais (GSCM) surge como uma estratégia para coordenar mais eficazmente as atividades dispersas geograficamente dos sistemas produtivos. Na adoção do GSCM, as organizações devem lidar com rupturas que impactam no gerenciamento das suas atividades, tais como a interrupção de vias de transporte, pane no fornecimento de energia, desastres naturais e até ataques terroristas. Nesse contexto, o trabalho introduz um procedimento sistematizado para modelagem das cadeias de suprimentos visto como um sistema a eventos discretos e sua análise por simulação das atividades do GSCM baseada em técnicas formais como a rede de Petri (PN) e o Production Flow Schema (PFS). Um exemplo é também apresentado para ilustrar e comprovar as vantagens do método proposto na análise do GSCM. / In a context of increasing competition, rising of expectations for product innovations and need to satisfy different consumer needs, the concept of global supply chain management (GSCM) emerges as a strategy to more efficiently coordinate the geographically dispersed activities of production systems. Adopting GSCM, organizations have to deal with external disruptions that impact management activities, such as transport interruption, power supply failure, natural disasters and terrorist attacks. In this way, a systematized procedure for modeling supply chains as a discrete event system and simulation analysis of GSCM activities based on formal techniques, such as Petri net (PN) and Production Flow Schema (PFS) is introduced. An example is also presented to illustrate and confirm the advantages of the proposed method for GSCM analysis.

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