The cores of galaxy clusters contain the most massive galaxies in the Universe, the brightest cluster galaxies. These galaxies are unique compared to their counterpart galaxies outside of clusters as they have much brighter cores, and vast spatially- extended stellar envelopes. The theoretical picture of how they reached their huge masses relied on the idea of gradual stellar mass growth during the second half of the history of the Universe. However, recent observational evidence of highly-overdense protoclusters, the progenitors of these galaxies, demonstrates that some brightest cluster galaxies may have assembled within the first few billion years after the Big Bang – seemingly contradicting our theoretical predictions. I include my theoretical work that shows the short timescales over which these observed protoclusters trans- form into the brightest cluster galaxies and discuss the likelihood of finding these rare protoclusters in the early Universe. To push our understanding of the rapid evolution of these galaxies even further for- ward demands the use of numerical simulations due to the highly coupled, non-linear astrophysical processes that occur during the process. In this dissertation, I include improvements to our numerical models of hydrodynamical turbulence and supermas- sive black holes that I incorporated into a state-of-the-art hydrodynamical+gravity simulation code, in effort to provide the groundwork to improving our understanding of the build-up of the brightest cluster galaxies in the early Universe, and galaxy evolution in general. / Graduate

No description available.

This licentiate thesis considers the modelling, simulation and experimental investigation of a rammer compactor machine. The purpose is to develop an efficient and verified method for simulation of rammer compactor machines to be used in the product development process. The experience gained through this work is also intended to be useful for studying other types of dynamic compactor machines. Rammer compactor machines perform impact soil compaction. This is more efficient than static compaction. The machines are often used in places where a high degree of compaction is needed, and where the space for operation is limited. The complexity of this type of machine makes design optimisation through traditional prototype testing impractical. This has pointed to the need for a theoretical model and simulation procedure for predicting the dynamic behaviour of the machine. To be useful for optimisation the theoretical model and simulation procedure must be verified. By concurrently working with theoretical modelling, simulations, experimental verifications, and optimisation an efficient analysis support for product development is achieved. This co-ordination works both ways in an iterative manner: experimental investigations are used to verify theoretical models and simulations; and theoretical models and simulations are used to design good experiments. This Complete Approach concept enables better decisions to be made earlier on in the development process, resulting in a decrease in time-to-market and improved quality. In this thesis, the Complete Approach concept is applied to a rammer soil compactor machine. An introductory iteration is described. The good agreement between theoretical and experimental results indicates that the theoretical model and simulation procedure should prove useful in introductory optimisation studies. The thesis discusses reasons for the remaining discrepancy and suggests improvements in both the theoretical model and the experimental set-up for future iterations. / I arbetet studeras det dynamiska beteendet av en jordpackningsmaskin. Syftet är att bygga upp en verifierad modell som kan ligga till grund för vidare produktutveckling. Ett samordnat arbetsätt, Complete Aproach / <p>http://epubl.luth.se/1402-/02/index.html</p>

La presente investigación se centra en la generación de mapas de peligro por la simulación del vertido de relaves por rotura de la presa del depósito de relaves en estado pulpa ubicada en el distrito de Chocó, en Colombia mediante un modelo hidrológico – hidráulico, y la posterior clasificación de los mapas de inundación y velocidad en niveles de peligrosidad. Este tipo de simulaciones requieren de un modelo numérico capaz de analizar y desarrollar el comportamiento de un flujo hiperconcentrado en la llanura de inundación aguas abajo. Las ecuaciones que controlan el movimiento de estos tipos de flujos son las aplicadas para fluidos no newtonianos, los cuales están controlados por los parámetros reológicos, como: viscosidad dinámica, esfuerzo de fluencia y la tasa de corte. Es por ello que se ha escogido el software FLO-2D el cual cuenta con facilidad de ingreso de datos y geometría, estabilidad de rutina computacional y la facilidad de lectura de archivos de salida. Los resultados obtenidos de la simulación en el distrito de Chocó muestran de manera didáctica la delimitación de zonas de riesgo de acuerdo a la clasificación de peligro en torno a velocidades y tirantes máximos. Eso nos permitió reconocer las estructuras que comprendidas en las zonas de alto riesgo. Estos mapas de peligro servirán como herramientas para evaluaciones de alcance social, ambiental y económico y la consideración y elección de medidas a corto, mediano y largo plazo, y de carácter tanto estructural, como no estructural. / This research focuses on the generation of hazard maps by simulating the discharge of tailings due to breakage of the dam of the pulp tailings deposit located in the Chocó district, in Colombia, using a hydrological-hydraulic model, and the subsequent classification of the flood and speed maps in danger levels. These types of simulations require a numerical model capable of analyzing and developing the behavior of a hyperconcentrated flow in the downstream floodplain. The equations that control the movement of these types of flows are those applied for non-Newtonian fluids, which are controlled by the rheological parameters, such as: dynamic viscosity, creep stress and the shear rate. That is why the FLO-2D software has been chosen which has ease of data entry and geometry, computational routine stability and ease of reading output files. The results obtained from the simulation in the Chocó district didactically show the delimitation of risk areas according to the hazard classification around maximum speeds and braces. This allowed us to recognize the structures included in high risk areas. These hazard maps will serve as tools for evaluations of social, environmental and economic scope and the consideration and choice of short, medium and long-term measures, both structural and non-structural. / Tesis

Dans cette thèse de doctorat, des simulations numériques basées sur un modèle fluide 2D sont utilisées pour caractériser des jets de plasma d’Hélium pulsés. Le modèle pour les jets de plasma d’Hélium est développé pour décrire des jets qui s’écoulent dans des atmosphères de N2 et O2 et interagissent avec des cibles. La dynamique de la décharge dans les jets d’Hélium impactant une cible métallique à la masse est analysée pour des polarités positive et négative de la tension appliquée. Les évolutions temporelles et spatiales de champ électrique associées au premier front d’ionisation et au front de rebond sont en bon accord qualitatif avec des mesures récentes de champ électrique. Puis, l’interaction plasma cible entre une décharge positive et une cible diélectrique en BSO est examinée en détail et les résultats sont directement comparés aux expériences. Un bon accord est obtenu entre les simulations et les expériences sur les évolutions temporelles et spatiales de champ électrique. Des valeurs maximales de champ électrique dans la cible de 5 kV.cm−1 ont été obtenues expérimentalement et numériquement. Le champ électrique dans le plasma de l’ordre de quelques dizaines de kV.cm−1 est fortement diminué par le changement de permittivité de la cible. Le champ électrique dans la cible est presque exclusivement dû aux fortes valeurs de charges de surface déposées sur la surface de la cible. Finalement, l’influence des évolutions de champ électrique sur la production d’espèces actives près des cibles est évaluée. On démontre qu’avec des cibles métalliques la synergie entre le premier front et le front de rebond augmente la production d’espèces près de la cible. / In this PhD thesis numerical simulations based on a 2D fluid model are used to characterize pulsed Helium plasma jets. The model for He plasma jets is developed to describe He jets flowing in N2 and O2 atmospheres and interacting with targets. The discharge dynamics in He jets impacting a grounded metallic target is analyzed with both positive and negative polarities of applied voltage. The temporal and spatial evolutions of electric field associated to the first and rebound ionization fronts are in good qualitative agreement with recent electric field measurements. Then, the plasma-target interaction occurring between a positive discharge and a BSO dielectric target is investigated in detail and results are directly compared with experiments. A good agreement is obtained between simulations and experiments concerning the temporal and spatial profiles of electric field. Maximum values of electric field inside the target of 5 kV.cm−1 are found. The high electric field in the plasma of the order of dozens of kV.cm−1 is severely depleted by the change of permittivity. As a result, the electric field experienced inside the target is almost exclusively originated by the high values of surface charge deposited on the target surface. Finally, the influence of the electric field evolutions on the production of chemically active species close to the targets is evaluated. It is shown that with metallic targets the synergy between the first and rebound fronts increases species production close to the target.

Indiana University-Purdue University Indianapolis (IUPUI) / Since the conception of three dimensional (3D) printing circa 40 years ago, there has been the proliferation of several additive manufacturing (AM) technologies that enable its use in everyday applications such as aerospace, medicine, military, oil and gas and infrastructure. In order to improve its applicability and growth, 3D printed materials are subjected to the same or even higher levels of scrutiny for its mechanical behavior as its conventionally manufactured counterpart. One of the most important mechanical properties is toughness or the ability of a material to undergo large strain prior to fracture when loaded. The toughness of a material can be correlated to its impact energy or the increase in internal energy due to impact. In this study, the impact properties, including the toughness of 3D printed 15-5 stainless steel were investigated at low temperature (77 K), room temperature (298 K) and high temperature (723 K) using experimental and numerical modeling of the Charpy impact test. In addition, ballistic impact simulations were performed to determine the applicability of 3D printed 15-5 stainless steel in the defense industry. The 15-5 stainless steel specimens were printed (horizontal-build) using the direct metal laser sintering (DMLS) technique, cooled or heated to the specified temperature, then tested in accordance with the ASTM E23-2016b [1] standard. The Johnson-Cook (J-C) phenomenological material model and fracture parameters were used in the numerical modeling. The cross-sectional microstructures of surfaces and impact energies of the Charpy impact test were examined. For the ballistic impact simulations, a 3D printed 15-5 stainless steel typical plate was investigated at the same temperatures as the Charpy impact test. A typical missile using the J-C properties at room temperature (298 K) was assigned an initial velocity of 300 ms-1 for each plate temperature. The fracture surface investigation (microsurface analysis as well as visual inspection) and impact energy values of the Charpy impact test show that the 3D printed 15-5 stainless steel exhibited brittle behavior at low and room temperatures, but transitioned into a more ductile behavior at high temperature. At 77 K, 298 K and 723 K, the experimental Charpy impact test results were 0.00 J/cm2, 6.78±4.07 J/cm2 and 50.84±3.39 J/cm2 respectively; whereas the simulated impact energy were 1.05 J/cm2, 10.46 J/cm2 and 47.07 J/cm2 respectively. Hence, the impact energy for the experimental and numerical simulations were in good agreement; especially at higher temperatures. Consistent with the results from the Charpy impact test, the ballistic impact simulations show an increase in the impact energy, elastic plastic strain and deflection of the plate with an increase in temperature indicating brittle-to-ductile behavior. The high exit velocity at low and room temperature may not make the plate attractive in defense in its current configuration; however, at the high temperature, the exit velocity reduction was significant.

Indiana University-Purdue University Indianapolis (IUPUI) / Pressure wave supercharger is an application of wave rotor technology that utilizes compression waves produced by high-pressure engine exhaust gas to compress the fresh intake air within the channels. The phenomena within the wave rotor channels are governed by compression and expansion waves initiated when the channel ends are periodically exposed to differing pressure ports. Two incoming fluids are brought into contact for a very short amount of time to facilitate efficient energy and momentum transfer, thereby exchanging pressure dynamically between the fluids by means of unsteady pressure waves. Since the energy transfer is based on unsteady pressure waves, correct matching of waves and ports is essential for optimum results. Mistiming of the waves in the channels is detrimental to the efficient exchange of pressure and low-pressure exhaust scavenging, which ensures minimum exhaust gas recirculation. Due to varying speed and load conditions of the unit to be supercharged, it is not always possible to maintain the rotor speed constant at the design point. To mitigate the effects of wave mistiming due to varying speed, a well-designed combination of wall-pockets was used in Comprex® pressure wave supercharger. The wall-pockets are the recesses provided in the endplates of pressure wave superchargers to create necessary pressure zones at desired locations. This thesis details an extensive qualitative and computational investigation of the performance of pressure wave superchargers with pockets. Numerical simulations of pressure wave superchargers have been performed using the wave rotor analysis codes employed at the Combustion and Propulsion Research Laboratory at IUPUI. This work also pays close attention to inspecting the numerical schemes and modeling of different physical phenomena used in each code. A comparative verification of the wave rotor analysis codes has been conducted to ensure that the same fundamental numerical scheme is correctly implemented in each code. The issue of low-pressure scavenging has been demonstrated by simulating the four-port (pocketless) pressure wave supercharger operating at lower speeds. The wall-pockets have been modeled using a simple lumped volume technique. The gas state in the lumped volume of pockets is estimated using the continuity and energy equations such that the net mass and energy fluxes between each pocket and the wave rotor channels are close to zero. The lumped volume models of pockets have been implemented in the four-port wave rotor configurations to simulate the pressure wave superchargers with pockets. The simulation results show that the pockets assist to maintain sufficient pressure in the desired zones to facilitate proper low-pressure scavenging during lower rotor speed operations. The Comprex simulation results have been observed to be in good agreement with experimental data and qualitative analysis. Specific observations on the performance of each code and comprehensive simulation results have been presented.

The thesis deals with numerical simulations of a hairpin thermionic electron gun, an electron source of the electron-beam welding machine. Simulations showed that the space charge in the electron gun has a significant influence on the beam current and electron trajectories. Simulation outputs are in a sufficient agreement with the experimental measurements.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18085号 / 理博第3963号 / 新制||理||1571(附属図書館) / 30943 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 藤 浩明, 教授 家森 俊彦, 教授 福田 洋一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18306号 / 工博第3898号 / 新制||工||1598(附属図書館) / 31164 / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 山本 量一, 教授 松坂 修二, 教授 古賀 毅 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM