京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20184号 / 理博第4269号 / 新制||理||1613(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 田口 聡, 教授 家森 俊彦, 教授 塩谷 雅人 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24618号 / 工博第5124号 / 新制||工||1979(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 大村 善治, 教授 松尾 哲司, 教授 小嶋 浩嗣 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Space-charge effects play a dominant role in many areas of physics. In high-power microwave devices using high-current, relativistic electron beams, it places a limit on the amount of radiation a device can produce. Because the beam's space-charge can actually reflect a portion of the beam, the ability to accurately predict the amount of current a device can carry is needed. This current value is known as the space-charge limited current. Because of the mathematical difficulties, this limit is typically estimated from a one-dimensional theory. This work presents a two-dimensional theory for calculating an upper-bound for the space-charge limited current of relativistic electron beams propagating in grounded coaxial drift tubes. Applicable to annular beams of arbitrary radius and thickness, the theory includes the effect introduced by a finite-length drift tube of circular cross-section. Using Green's second identity, the need to solve Poisson's equation is transferred to solving a Sturm-Liouville eigenvalue problem, which is easily solved by elementary methods. In general, the resulting eigenvalue, which is required to estimate the limiting current, must be numerically determined. However, analytic expressions can be found for frequently encountered limiting cases. Space-charge effects also produce the fundamental collective behavior found in plasmas, especially in plasma sheaths. A plasma sheath is the transition region between a bulk plasma and an adjacent plasma-facing surface. The sheath controls the loss of particles from the plasma in order to maintain neutrality. Using a fully kinetic theory, the problem of a planar sheath with a single-minimum electric potential profile is investigated. Appropriate for single charge-state ions of arbitrary temperature, the theory includes the emission of warm electrons from the surface as well as a net current through the sheath and is compared to particle-in-cell simulations. Approximate expressions are developed for estimating the sheath potential as well as the transition to space-charge saturation. The case of a space-charge limited sheath is discussed and compared to the familiar Child-Langmuir law.

Battery technology is a great candidate for energy storage applications. The need for high-performance and cost-effective batteries has motivated researchers to put much effort into improving battery performance. In this work, we attempt to understand the elements that affect the microstructure and performance of two battery systems. The first part of this work focuses on the investigation of transport and structural properties of porous electrodes in an alkaline electrolyte. A DC polarization method was deployed for tortuosity measurements. An apparatus was designed to flow specified current through and measure the voltage drop over the porous electrodes. Using a modified Ohm's law, effective diffusion coefficient and associated tortuosity were determined. Multiple compositions (different types and amounts of conductive additives) were tested to understand the effects of composition on the transport properties. As a validation and to further understand the tests, a model was developed and used for data analysis. The second part of this dissertation describes simulations of the manufacturing process of a Li-ion electrode. LAMMPS, a particle simulator, was used for this meso-scale particle-based simulation. The interactions between particles were understood by model-experiment comparisons of the macroscopic properties such as viscosity of the slurry and elasticity of the dried film. The microstructure created by this simulation was consistent with the one we observed in SEM/ FIB images. Although the emphasis was the drying process in this part, some preliminary coating and calendering simulations are presented. Finally, the effects of electrode heterogeneity were investigated by a Newman-type model and tomographic images. An electronic conductivity map was initially generated over a Li-ion cathode. Then SEM/FIB images of specified high, middle, and low conductivity regions were taken to confirm heterogeneity. For modeling purposes, three regions of high, middle, and low ionic resistance were considered connected in parallel, representing the real electrode heterogeneity. Multiple cases of heterogeneities such as non-uniform ionic resistance and active material loading at low, middle, and high charge-discharge rates were studied. The results show that higher rates increase non-uniformities of dependent properties such as temperature, current density, positive and negative electrodes states of charge, and charge and discharge capacities especially in charging cases.

Particle systems are used to create visual effects in real-time applications such as computer games. However, emitted particles are often transient and do not leave a lasting impact on a 3D scene. This thesis work presents a real-time method that enables GPU particle systems to paint meshes in a 3D scene as the result of particle collisions, thus adding detail to and leaving a lasting impact on a scene. The method uses screen space collision detection and a mapping from screen space to texture space of meshes to determine where to apply paint. The method was tested for its time complexity and how well it performed in scenarios similar to those found in computer games. The results shows that the method probably can be used in computer games. Performance and visual fidelity of the paint application is not directly dependent on the amount of simulated particles, but depends only on the complexity of the meshes and their texture mapping as wellas the resolution of the paint. It is concluded that the method is renderer agnostic and could be added to existing GPU particle systems and that other types of effects than those showed in the thesis could be achieved by using the method.

Background. With the introduction of the compute shader, followed by the application programming interface (API) DirectX 12, the modern GPU is now going through a transformation. Previously the GPU was used as a massive computational tool for running a single task at unparalleled speed. The compute shader made it possible to run CPU like programs on the GPU, DirectX 12 takes this even further by introducing a multi-engine architecture. Multi-engine architecture unlocks the possibility of running the compute shader alongside the regular graphical stages, this concept is called asynchronous compute. Objectives. This thesis aims to investigate if asynchronous compute can be used to increase the performance of particle simulations. The key metrics being studied are total frame time, rendered frames per second, and overlap time. The frst two are used to determine if asynchronous compute improves performance or not, while the last is used to determine if the particle simulation is running asynchronous compute or not.Methods. For this thesis, the particle simulation used is the N-body particle simulation.The N-body particle simulation is implemented using a compute shader and is part of a larger DirectX 12 framework. One application is implemented that run two different execution models, one is the standard sequential execution model and one is the asynchronous compute model. The main difference between the two execution models is that the sequential execution model will be using only one command queue, this being a 3D command queue. The asynchronous compute model will be running a separate compute command queue alongside the 3D command queue. The performance metrics being studied are all collected using a custom-built GPU profiler. Results. The results indicate that it is possible to increase the performance of particle simulations using asynchronous compute. The registered performance gain reaches as high as 34% on hardware that supports asynchronous compute while hardware that according to NVIDIA does not support asynchronous compute registered performance gains up towards 11%. In terms of overlap time between the compute workload and the graphical workload, the AMD GPU showed an overlap time that matched the frame time. However, NVIDIA GPUs did not show the expected overlap time. Conclusions. It can be determined that asynchronous compute provide benefits when compared to the sequential execution model, it can be used to increase the performance of particle simulations. However, since the research in this thesis only made use of a single particle simulation, more work needs to be done, for example, work to test if the performance gain can be improved even further using different methods like, workload pairing or utilizing multiple GPUs, however that kind of work requires the use of a larger-scale application that consists of multiple different tasks other than just a single particle simulation. / Bakgrund. I och med Introduktionen av compute shadern, tätt följd av DirectX12, så genomgår den moderna GPUn en förvandling. Tidigare användes GPUn som ett massivt uträkningsverktyg ämnat att utföra en enda uppgift med en enastående hastighet. Compute shadern gjorde det möjligt at köra CPU liknande program på GPUn, DirectX 12 tar detta ett steg längre genom att introducera en multi-engine arkitektur. Denna arkitektur låser upp möjligheten att köra compute shadern samtidigt som de vanliga grafiska shader stadigerna, detta konceptet kallas asynchronous compute.Syfte. Syftet med denna avhandling är att undersöka om asynchronous compute kan användas för att öka prestandan på en partikel simulering. Den viktigaste data som kommer studeras är den totala frame tiden, antalet renderade frames varje sekund och överlapp tiden. Den totala frame tiden och antalet renderade frames varje sekund används för att bestämma om asynchronous compute faktiskt ökar prestandan eller inte, medan överlapp tiden används för att bestämma om partikel simuleringen kör asynchronous compute eller inte.Metod. Partikel simuleringen som används i denna avhandling är en N-body partikel simulering. N-body partikel simuleringen är implementerad i en compute shader och är en del av en större DirectX 12 applikation. En applikation implementeras som kör två olika exekverings modeller, den ena är den vanliga sekventiella exekverings modellen och den andra är asynchronous compute modellen. Den primära skillnaden mellan exekverings modellerna är att den sekventiella exekverings modellen bara använder sig av en kommando kö, vilken är en 3D kommando kö. Asynchronous compute modellen kommer använda sig av en separat compute kommando kö tillsammans med 3D kommando kön. Den metriska datan samlas in med hjälp av enegen byggd GPU profilerare.Resultat. Resultatet indikerar att det är möjligt att öka prestandan hos en partikelsimulering som använder sig av asynchronous compute. Den registrerade prestandaökningen når så högt som till 34% på hårdvara som stödjer asynchronous compute, medan hårdvara som inte stödjer asynchronous compute registrerade en prestandaökning upp till 11%. När det kommer till överlapp tiden mellan compute delen och den grafiska delen så visar GPUn från AMD en överlapp tid som matchar frame tiden. När det kommer till GPUerna från NVIDIA så visade dessa inte en förväntad överlapp tid.Slutsatser. Det kan fastställas att asynchronous compute har vissa fördelar jämfört med den sekventiella exekverings modellen. Asynchronous compute kan användas för att öka prestanda hos partikel simuleringar, men eftersom undersökningen i denna avhandling bara använder en enda partikel simulering så krävs ännu mera forskning. Exempelvis forskning som undersöker om prestanda ökningen kan bli ännu bättre, genom att applicera olika metoder som workload pairing och användingen av fera GPUer, detta krväver också att en större application för testing används, som består av fera olika typer av simuleringar och inte bara en enda partikel simuleing.

Mit zunehmenden mineralischen Ressourcenbedarf steigen die Anforde-rungen an Aufbereitungsmaschinen wie den Center-Sizer. Um diesen An-forderungen gerecht zu werden, lag der Schwerpunkt bisher in der Ver-besserung der maschinenseitigen Modellbeschreibung, wobei für die Ma-terialmodelle zumeist stark vereinfacht blieben. Die vorliegende Arbeit behandelt die Entwicklung eines materialseitigen Modells basierend auf der Diskreten-Elemente-Methode, welches durch eine begründete Parametrierung sowie in Co-Simulation mit einem mehr-dimensionalen Maschinenmodell zur Belastungsprognose auf Center-Sizer dient. Sie leistet damit einen Beitrag zur Erweiterung der bestehenden Auslegungsmethode und bietet für weiterführende Forschungstätigkeiten eine substanzielle Grundlage. / As the demand for mineral resources increases, so do the requirements for processing machines such as the Center-Sizer. In order to meet these re-quirements, the focus has so far been on improving the model description on the machine side, whereby the material models mostly have remained simplified. The present dissertation deals with the development of a material model based on the discrete-element-method for the load prediction on center sizer by using determined parameterization method as well as the co-simulation with a multidimensional machine model. It contributes to the enhancement of the current method of structural design and it serves a substantial basis for further research projects.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21732号 / 工博第4549号 / 新制||工||1709(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 大村 善治, 教授 松尾 哲司, 教授 竹内 繁樹 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Recently observed cumulation of unexpected collapses of slope-distant waste dumps in lignite mining areas of eastern germany re-initiated research of soil liquefaction. Especially it turned the question of internal initials that correspond to water rise. Parallel to laboritory tests and field experiments a micromechanical model should be developed, which can reproduce processes in the soil during saturation. In first approximation a partly saturated soil consists of two phases: the soil particles and the pore fluid. For micromechanical modeling a coupling of discontinuum particles) and continuum (fluid) is required. The soil particles can be simulated with the Discrete-Element-Method (DEM). For the pore fluid, which is assumed to be a mixture of liquid and gaseous fractions, Pore scale model with Finite Volumes (PFV) is used. At low water content liquid bridges (meniscii) arise between the particles that cause an apparent cohesion. The effect of the meniscii is considered by a correspondingly contact law in the DEM model. During the saturation of a soil both, cohesive effect and fluid bulk modulus, are reduced. In addition buoyancy acts on the particles during the process. The micromechanical modeling approach has the advantage, that just a few model parameters are needed. The numerical model shows pore fluid pressures during saturation process, that leads to a reduction of effective stress. It is investigated how much the reduction is regarding porosity, degree of saturation, stress conditions and grain shape. Furthermore the influence of model parameters as well as hydromechanics is investigated. The investigations are completed with another series of experiments under special conditions like integration of macropores, horizontal fixed model boundaries and abrupt saturation.

Partikelsimulationen repräsentieren eine Klasse von daten- und rechenintensiven Simulationsanwendungen, die in unterschiedlichen Bereichen der Wissenschaft und der industriellen Forschung zum Einsatz kommen. Der hohe Berechnungsaufwand der eingesetzten Lösungsmethoden und die großen Datenmengen, die zur Modellierung realistischer Probleme benötigt werden, machen die Nutzung paralleler Rechentechnik hierfür unverzichtbar. Parallelrechner mit verteiltem Speicher stellen dabei eine weit verbreitete Architektur dar, bei der eine Vielzahl an parallel arbeitenden Rechenknoten über ein Verbindungsnetzwerk miteinander Daten austauschen können. Die Berechnung von Wechselwirkungen zwischen Partikeln stellt oft den Hauptaufwand einer Partikelsimulation dar und wird mit Hilfe schneller Lösungsmethoden, wie dem Barnes-Hut-Algorithmus oder der Schnellen Multipolmethode, durchgeführt. Effiziente parallele Implementierungen dieser Algorithmen benötigen dabei eine Sortierung der Partikel nach ihren räumlichen Positionen. Die Sortierung ist sowohl notwendig, um einen effizienten Zugriff auf die Partikeldaten zu erhalten, als auch Teil von Optimierungen zur Erhöhung der Lokalität von Speicherzugriffen, zur Minimierung der Kommunikation und zur Verbesserung der Lastbalancierung paralleler Berechnungen. Die vorliegende Dissertation beschäftigt sich mit der Entwicklung eines effizienten parallelen Sortierverfahrens und der dafür benötigten Kommunikationsoperationen zur Datenumverteilung in Partikelsimulationen. Hierzu werden eine Vielzahl existierender paralleler Sortierverfahren für verteilten Speicher analysiert und mit den Anforderungen von Seiten der Partikelsimulationsanwendungen verglichen. Besondere Herausforderungen ergeben sich dabei hinsichtlich der Aufteilung der Partikeldaten auf verteilten Speicher, der Gewichtung zu sortierender Daten zur verbesserten Lastbalancierung, dem Umgang mit doppelten Schlüsselwerten sowie der Verfügbarkeit und Nutzung speichereffizienter Kommunikationsoperationen. Um diese Anforderungen zu erfüllen, wird ein neues paralleles Sortierverfahren entwickelt und in die betrachteten Anwendungsprogramme integriert. Darüber hinaus wird ein neuer In-place-Algorithmus für der MPI_Alltoallv-Kommunikationsoperation vorgestellt, mit dem der Speicherverbrauch für die notwendige Datenumverteilung innerhalb der parallelen Sortierung deutlich reduziert werden kann. Das Verhalten aller entwickelten Verfahren wird jeweils isoliert und im praxisrelevanten Einsatz innerhalb verschiedener Anwendungsprogramme und unter Verwendung unterschiedlicher, insbesondere auch hochskalierbarer Parallelrechner untersucht.