Contribution of the two rectifiers reconfiguration to fault tolerance connected to the grid network to feed the GMAW through processor-in-the-loop

This study aims to propose a new diagnosis technique based on the Park’s vector and the polar coordinates of electric currents for the detection and location of open-circuit faults (OC) at the level of two rectifiers connected to the grid network to feed the Gas Metal Arc Welding process (GMAW). This diagnosis technique allows the early location of faulty switches (Thyristors) to overcome the negative effect of faulty rectifiers on welding current, welding voltage, and droplet diameter. For that, the reconfigurable rectifiers have been integrated to accomplish the welding process. The proposed diagnosis technique is applied to reconfigurable rectifiers connected to the GMAW system through numerical simulations using MATLAB/Simulink and real-time processor-in-the-loop (PIL) implementation via DSpace ds 1103 card. The simulation and PIL experimental results show similar trends and great success of the diagnosis technique and the two rectifiers reconfiguration for overcoming the open circuit faults and obtaining high welding quality while maintaining the work-piece and avoiding the distortions caused by the faulty rectifiers, which affecting the grid network and on the GMAW system at the same time

Developments in Directed Energy Deposition Additive Manufacturing: In-situ Hot Forging and Indirect Cooling

Additive Manufacturing (AM) by Directed Energy Deposition-arc (DED-arc) is competing with other AM technologies due to its high deposition rate, ability to produce large parts with medium/high geometric complexity and low capital and running costs. However, residual stresses, coarse microstructures, and defects on parts, such as cracks and pores, may compromise in-service industrial applications and need to be overcome. This work aimed to develop and validate two innovative process variants: one based on in-situ hot forging; and the other on temperature control, that is, indirect cooling of deposited material and hot forging. The hot forging variant consisted of locally forging the deposited layer at high temperatures using low forces. The goal is to create an uniform plastic deformation zone along the layer, to promote grain refinement, reduce material anisotropy and collapse defects. The variant based on temperature control consisted of cooling the hammer components and the shielding gas used to protect the molten pool, to increase the solidification rate and thus, prevent grain coalescence. For this, dedicated DED-arc equipment was designed and manufactured with specific features for research. The effect of hot forging was analysed in detail on 316LSi stainless steel, and the feasibility of its application was verified in other relevant industrial materials. It was concluded that hot forging can induce dynamic recrystallization, increase nucleation sites and prevent epitaxial grain growth. Thus, it contributes to an overall refined and homogeneous microstructure with improved mechanical properties. The developed cooling system lowered the average temperature of the nozzle and hammer during consecutive depositions. Cooling of the shielding gas had no major effect on the cooling rates and microstructure of the materials, however, it was observed that the hot forging changes the heat flow conditions of the part, promoting higher cooling rates.A tecnologia de deposição direta de energia por arco (DED-arc) tem competido com outras tecnologias de fabrico aditivo devido à sua elevada taxa de deposição, capacidade de produzir componentes de grandes dimensões com média/alta complexidade geométrica e baixos custos de implementação e funcionamento. Contudo, as elevadas tensões residuais, as microestruturas grosseiras, ou os defeitos do tipo poros, podem comprometer algumas aplicações industriais e necessitam de ser superados. Este trabalho visou desenvolver e validar duas variantes inovadoras de processo DED- arc: uma baseada no forjamento a quente; e outra no controlo de temperatura. A variante baseada no forjamento, consistiu em forjar o material depositado imediatamente após a deposição, utilizando baixas forças. O objetivo foi a produção de uma zona de deformação plástica uniforme ao longo de cada camada, para promover alterações microestruturais, nomeadamente o refinamento dos grãos e a redução da anisotropia. A variante baseada no trabalho termodinâmico consistiu em arrefecer os componentes do martelo e o gás utilizado para proteger o banho de fusão, com o objetivo de aumentar a taxa de arrefecimento e assim evitar a coalescência dos grãos. Neste sentido, foi concebido e fabricado um equipamento de DED-arc, com características específicas para investigação. O efeito do forjamento a quente foi estudado detalhadamente no aço inoxidável 316LSi, e foi verificada a viabilidade da sua aplicação noutros materiais relevantes industrialmente. Concluiu-se que o forjamento induz recristalização dinâmica, aumenta os pontos de nucleação e impede o crescimento de grãos epitaxiais, contribuindo para uma microestrutura globalmente mais fina, homogénea e com melhores propriedades mecânicas. O sistema de arrefecimento desenvolvido baixou a temperatura do bocal e do martelo durante as deposições consecutivas. O arrefecimento do gás de proteção não teve efeito nas taxas de arrefecimento nem na microestrutura do material, contudo, observou-se que o forjamento altera as condições de fluxo de calor, promovendo taxas de arrefecimento maiores

Design studies towards a 4 MW 170 GHz coaxial-cavity gyrotron

In this work the feasibility of a 4 MW 170 GHz coaxial-cavity gyrotron for continuous wave operation is demonstrated. For the first time complete physical designs of the major gyrotron components are elaborated. In a first step, one possible new operating mode is determined, followed by the development of detailed physical designs of the major gyrotron components: Diode and triode type electron gun, coaxial cavity, two-beam quasi-optical output coupler and depressed collector

Design of a high-power 48GHz gyroklystron amplifier for accelerator applications

As the technology of radiofrequency linear accelerators (RF linacs) continues to improve, higher frequency acceleration systems become of interest as the achievable acceleration gradient has a dependence on frequency. Using a high driving frequency requires the consideration of many technological challenges. One such challenge is mitigating the effect of nonlinearities introduced during the electron acceleration and bunching process. To counteract the nonlinearity, an additional cavity at a harmonic of the main driving frequency can be included. This technique is known as harmonic linearisation. In existing C-band systems, harmonic linearisation can be achieved with an X-band structure, but if the main frequency is X-band, the lineariser must be Ka-band or higher. Linear klystrons are a well-developed technology and can reliably deliver tens of MW at X-band, but they are subject to a steep drop-off in achievable output power toward the Ka-band. The different interaction mechanism in a gyroklystron, based on phase-modulation of a helical beam, allows it to deliver multi-MW output power at significantly higher frequencies. The gyroklystron is therefore a strong candidate for delivering power to high-frequency linearising cavities. The international collaboration, CompactLight, is developing a design for a sophisticated X-ray Free Electron Laser (XFEL) with wide ranging research applications [1, 2]. The project required the consideration of both a 36GHz and 48GHz lineariser options. In each case, the development of new amplifiers was required to deliver sufficient power for the application. This thesis presents the design and analysis of a gyroklystron appropriate to drive a 48GHz linearising cavity. While the research presented in this thesis was performed with direct consideration of the CompactLight XFEL, its relevance is not exclusive to this project. With the performance of the microwave amplifier presented in this thesis, a lineariser at 48GHz could be a viable option for other C-band or X-band accelerator applications. Gyroklystron research was historically focused on radar applications. Since 48GHz lies in a frequency band unfavourable for atmospheric transmission, the development of components in this band has been lacking. The design presented in this thesis is the first published work on a MW-level amplifier at 48GHz and marks a step toward this frequency becoming a desirable choice for linearisation systems in future linacs. A gyroklystron design, including the electron source, vacuum windows, and input coupler has been designed through detailed simulation work. A triode-type magnetron injection gun compatible with a 2.02T axial guide magnetic field was designed and simulated. Applying -140kV to the cathode and -107.5kV to the modulating anode resulted in a gyrating electron beam with a current of 37A, guiding centre radius of 1.77mm, and velocity ratio spread of 8.9%. This resulted in a predicted gyroklystron output power of 2.0MW with a gain of 35dB at an efficiency of 38.6%.As the technology of radiofrequency linear accelerators (RF linacs) continues to improve, higher frequency acceleration systems become of interest as the achievable acceleration gradient has a dependence on frequency. Using a high driving frequency requires the consideration of many technological challenges. One such challenge is mitigating the effect of nonlinearities introduced during the electron acceleration and bunching process. To counteract the nonlinearity, an additional cavity at a harmonic of the main driving frequency can be included. This technique is known as harmonic linearisation. In existing C-band systems, harmonic linearisation can be achieved with an X-band structure, but if the main frequency is X-band, the lineariser must be Ka-band or higher. Linear klystrons are a well-developed technology and can reliably deliver tens of MW at X-band, but they are subject to a steep drop-off in achievable output power toward the Ka-band. The different interaction mechanism in a gyroklystron, based on phase-modulation of a helical beam, allows it to deliver multi-MW output power at significantly higher frequencies. The gyroklystron is therefore a strong candidate for delivering power to high-frequency linearising cavities. The international collaboration, CompactLight, is developing a design for a sophisticated X-ray Free Electron Laser (XFEL) with wide ranging research applications [1, 2]. The project required the consideration of both a 36GHz and 48GHz lineariser options. In each case, the development of new amplifiers was required to deliver sufficient power for the application. This thesis presents the design and analysis of a gyroklystron appropriate to drive a 48GHz linearising cavity. While the research presented in this thesis was performed with direct consideration of the CompactLight XFEL, its relevance is not exclusive to this project. With the performance of the microwave amplifier presented in this thesis, a lineariser at 48GHz could be a viable option for other C-band or X-band accelerator applications. Gyroklystron research was historically focused on radar applications. Since 48GHz lies in a frequency band unfavourable for atmospheric transmission, the development of components in this band has been lacking. The design presented in this thesis is the first published work on a MW-level amplifier at 48GHz and marks a step toward this frequency becoming a desirable choice for linearisation systems in future linacs. A gyroklystron design, including the electron source, vacuum windows, and input coupler has been designed through detailed simulation work. A triode-type magnetron injection gun compatible with a 2.02T axial guide magnetic field was designed and simulated. Applying -140kV to the cathode and -107.5kV to the modulating anode resulted in a gyrating electron beam with a current of 37A, guiding centre radius of 1.77mm, and velocity ratio spread of 8.9%. This resulted in a predicted gyroklystron output power of 2.0MW with a gain of 35dB at an efficiency of 38.6%

Modeling, Numerical Analysis, and Predictions for the Detonation of Multi-Component Energetic Solids

Metal powders are often used as an additive to conventional high explosives to enhance the post-detonation blast wave. Piston-impact simulations are commonly utilized to predict performance metrics such as detonation speed and strength, as well as assessing the impact and shock sensitivity of these materials. The system response is strongly influenced by the initial particle size distribution and material composition. Multiphase continuum models have been routinely applied at the macroscale to characterize the detonation of solid high explosives over engineering length scales. Current models lack a description of the physically permissible constitutive relations for mass transfer due to general chemical reactions between multiple components. The model developed in this study is a major extension of one formulated for an inert mixture to include these reactions, which features a rigorous analysis of the energetic processes that identically satisfy the Second Law of Thermodynamics. Additional features of the model include evolutionary equations which predict phase temperature changes due to individual dissipative heating processes. Macroscale models often include nonconservative source terms that prevent the system of evolutionary equations from being posed in divergence form. A significant challenge in the development of numerical methods to solve these model equations is the proper inclusion of discretizations for the nonconservative sources. In the present work a novel modification of a centered finite-volume scheme is formulated, which is a rigorous extension of a conservative method to include nonconservative sources. This numerical scheme was used to perform a parametric study of metalized explosives containing the high explosive HMX (C4H8N8O8), with both inert and reactive aluminum. Wave speeds, structures, and energetics were shown to exhibit a strong dependence on metal grain size, with reactive aluminum significantly accelerating the detonation speed for the mixture above that of pure HMX for d_m \u3c 500 nm

Welding Processes

Despite the wide availability of literature on welding processes, a need exists to regularly update the engineering community on advancements in joining techniques of similar and dissimilar materials, in their numerical modeling, as well as in their sensing and control. In response to InTech's request to provide undergraduate and graduate students, welding engineers, and researchers with updates on recent achievements in welding, a group of 34 authors and co-authors from 14 countries representing five continents have joined to co-author this book on welding processes, free of charge to the reader. This book is divided into four sections: Laser Welding; Numerical Modeling of Welding Processes; Sensing of Welding Processes; and General Topics in Welding

Flow and transport in saturated and unsaturated fractured porous media: Development of particle-based modeling approaches

Das Ziel der vorliegenden Arbeit ist die Entwicklung von partikelbasierenden Strömungs- und Transportmodellen zur Charakterisierung von kleinskaligen Strömungsprozessen in gesättigten und ungesättigten Poren- und Kluftsystemen. Aufgrund der unzureichenden Prozessbeschreibung von ungesättigter Strömung in Doppelkontinuummodellen mittels der Richardsgleichung und van Genuchten Parametern werden innovative Methoden präsentiert um die zugrunde liegenden hochdynamischen Strömungs- und Transportprozesse zu erfassen. Die Simulation von Strömung und Transport in ungesättigten geklüfteten Aquiferen bildet immer noch ein höchst anspruchsvolles Aufgabenfeld aufgrund von skalenübergreifenden Diskontinuitäten, welche oftmals die Definition eines globalen repräsentativen Einheitsvolumens nicht zulassen. Des Weiteren können die hydraulischen Eigenschaften und potentiellen Parameterräume von geklüfteten Aquiferen oftmals nur durch integrale Ansätze, wie z.B. Pump- und Slugtests, Zeitreihenanalysen von Quellschüttungen und Tracertests ermittelt werden. Doppelkontinuummodelle bieten hierfür einen ausgewogenen Ansatz hinsichtlich der erforderlichen Felddaten und der resultierenden prädiktiven Modellqualität. Der erste Teil dieser Arbeit evaluiert den Doppelkontinuumansatz, welcher die Simulation von Strömung mittels der Richardsgleichung und van Genuchten Parametern in zwei, durch einen linearen Austauschterm gekoppelten, Kontinua ermöglicht. Ganglinien von Karstquellen weisen eine charakteristischen steilen Abfall nach Niederschlagsereignissen auf, der durch das Modell erfolgreich reproduziert werden kann. Das Röhrensystem bildet die hydraulische Brücke zur Karstquelle und nimmt potentialabhängige Wassermengen des geklüfteten Matrixsystems auf. Um die Simulation von schneller Grundwasserinfiltration durch das Röhrenkontinuum innerhalb der ungesättigten Zone zu vermeiden wurde die entsprechende Randbedingung an die untere Grenze des Kontinuums gesetzt. Ein genereller Nachteil des Doppelkontinuumsansatz ist die potentielle Mehrdeutigkeit von Modellergebnissen. Der duale Parameterraum in Kombination mit schwierig zu ermittelnden Parametern, führt zur Existenz von mehr als einem kalibrierten Modell, wie durch mehrdimensionale Sensitivitätsanalysen aufgezeigt wird.  Insbesondere in Karstaquiferen bilden Diskontinuitäten, wie z.B. Lösungsdolinen, Klüfte und Störungssysteme, bevorzugte hydraulische Elemente für schnelle vertikale Grundwasserneubildungsprozesse, die oftmals nicht durch volumeneffektive Modellansätze erfasst werden können. Der Hauptteil dieser Arbeit befasst sich daher mit der Entwicklung von zwei Smoothed Particle Hydrodynamics (SPH) Modellen um ein adäquates numerisches Werkzeug zur partikelbasierenden Simulation von kleinskaligen Strömungen mit freien Oberflächen und Transportprozessen bereitzustellen. SPH Modelle ermöglichen eine Eulersche Beschreibung eines Strömungsfelds auf Basis der Navier-Stokes Gleichung und Partikelbewegung mittels klassischer Newtonscher Mechanik. Der gitterlose Modellansatz ermöglicht flexible Simulationen von hochdynamischen Phasengrenzen in ungesättigten Klüften und Porenräumen. Das erste SPH Modell wird eingesetzt um durch Oberflächenspannung dominierte Tropfen- und Filmströmungen auf glatten und rauhen Kluftoberflächen zu simulieren. Charakteristische dimensionslose Kennzahlen werden über einen weiten Bereich von Benetzungswinkeln und Reynoldszahlen bestimmt. Modellergebnisse weisen einen hervorragende Übereinstimmung mit dimensionslosen Skalierungsfunktionen auf und kritische Kontaktwinkel folgen der zu erwartenden Entnetzungsdynamik. Die Entstehung von adsorbierten Filmen auf trockenen Oberflächen wird für einen breiten Parameterraum bestimmt. Des Weiteren wird der Einfluss von befeuchteten Oberflächen auf die Geschwindigkeitszunahme von Tropfenströmung aufgezeigt und so die Bedeutung der Koexistenz verschiedener Strömungsmodi gezeigt. Der Effekt von Oberflächenrauhigkeit auf Tropfenströmung wird für verschiedene Rauhigkeiten ermittelt und eine deutliche Geschwindigkeitsabnahme demonstriert. Um die makroskopische Kontinuumsbeschreibung der Navier-Stokes Gleichung und atomistische Effekte eines klassischen Partikelsystems der statistischen Mechanik zu kombinieren wurde ein zweites mesoskopisches SPH Modell entwickelt. Diese neue Diskretisation der vollständig gekoppelten Landau-Lifshitz-Navier-Stokes und Advektions- Diffusionsgleichung ermöglicht die Simulation von Strömung und Transport bei gleichzeitiger Berücksichtigung von Fluktuationsdynamiken, welche sich korrekt der Systemskala anpassen. Die Verbindung von klassischer Fickscher Diffusion und thermodynamischen Fluktuationen wird hierbei durch einen effektiven Diffusionskoeffizienten beschrieben. Numerische Experimente zeigen die Präzision des Modells. Grenzflächen zwischen zwei Fluiden unterschiedlicher Konzentration weisen eine korrekte Wellenzahldivergenz entsprechend aktuellen Laborergebnissen auf