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1
Pauthenet, Martin. "Macroscopic model and numerical simulation of elastic canopy flows." Thesis, Toulouse, INPT, 2018. http://www.theses.fr/2018INPT0072/document.
Abstract:
On étudie l'écoulement turbulent d'un fluide sur une canopée, que l'on modélise comme un milieu poreux déformable. Ce milieu poreux est en fait composé d'un tapis de fibres susceptibles de se courber sous la charge hydrodynamique du fluide, et ainsi de créer un couplage fluide-structure à l'échelle d'une hauteur de fibre (honami). L'objectif de la thèse est de développer un modèle macroscopique de cette interaction fluide-structure, afin d'en réaliser des simulations numériques. Une approche numérique de simulation aux grandes échelles est donc mise en place pour capturer les grandes structures de l'écoulement et leur couplage avec les déformations du milieu poreux. Pour cela nous dérivons les équations régissant la grande échelle, au point de vue du fluide ainsi que de la phase solide. À cause du caractère non-local de la phase solide, une approche hybride est proposée. La phase fluide est décrite d'un point de vue Eulerien, tandis que la description de la dynamique de la phase solide nécessite une représentation Lagrangienne. L'interface entre le fluide et le milieu poreux est traitée de manière continue. Cette approche de l'interface fluide/poreux est justifiée par un développement théorique sous forme de bilan de masse et de quantité de mouvement à l'interface. Ce modèle hybride est implémenté dans un solveur écrit en C$++$, à partir d'un solveur fluide disponible dans la librairie CFD \openfoam. Un préalable nécessaire à la réalisation d'un tel modèle macroscopique est la connaissance des phénomènes de la petite échelle en vue de les modéliser. Deux axes sont explorés concernant cet aspect. Le premier consiste à étudier les effets de l'inertie sur la perte de charge en milieu poreux. Un paramètre géométrique est proposé pour caractériser la sensibilité d'une microstructure poreuse à l'inertie de l'écoulement du fluide dans ses pores. L'efficacité de ce paramètre géométrique est validée sur une diversité de microstructures et le caractère général du paramètre est démontré. Une loi asymptotique est ensuite proposée pour modéliser les effets de l'inertie sur la perte de charge, et comprendre comment celle-ci évolue en fonction de la nature de la microstructure du milieu poreux. Le deuxième axe d'étude de la petite échelle consiste à étudier l'effet de l’interaction fluide-structure à l'échelle du pore sur la perte de charge au niveau macroscopique. Comme les cas présentent de grands déplacements de la phase solide, une approche par frontières immergées est proposée. Ainsi deux méthodes numériques sont employées pour appliquer la condition de non-glissement à l'interface fluid/solide: l'une par interface diffuse, l'autre par reconstitution de l'interface. Cela permet une validation croisée des résultats et d'atteindre des temps de calcul acceptables tout en maîtrisant la précision des résultats numériques. Cette étude permet de montrer que l'interaction fluide-structure à l'échelle du pore a un effet considérable sur la perte de charge effective au niveau macroscopique. Des questions fondamentales sont ensuite abordées, telles que la taille d'un élément représentatif ou la forme des équations de transport dans un milieu poreux soupleWe study the turbulent flow of a fluid over a canopy, that we model as a deformable porous medium. This porous medium is more precisely a carpet of fibres that bend under the hydrodynamic load, hence initiating a fluid-structure coupling at the scale of a fibre's height (honami). The objective of the thesis is to develop a macroscopic model of this fluid-structure interaction in order to perform numerical simulations of this process. The volume averaging method is implemented to describe the large scales of the flow and their interaction with the deformable porous medium. An hybrid approach is followed due to the non-local nature of the solid phase; While the large scales of the flow are described within an Eulerian frame by applying the method of volume averaging, a Lagrangian approach is proposed to describe the ensemble of fibres. The interface between the free-flow and the porous medium is handle with a One-Domain- Approach, which we justify with the theoretical development of a mass- and momentum- balance at the fluid/porous interface. This hybrid model is then implemented in a parallel code written in C$++$, based on a fluid- solver available from the \openfoam CFD toolbox. Some preliminary results show the ability of this approach to simulate a honami within a reasonable computational cost. Prior to implementing a macroscopic model, insight into the small-scale is required. Two specific aspects of the small-scale are therefore studied in details; The first development deals with the inertial deviation from Darcy's law. A geometrical parameter is proposed to describe the effect of inertia on Darcy's law, depending on the shape of the microstructure of the porous medium. This topological parameter is shown to efficiently characterize inertia effects on a diversity of tested microstructures. An asymptotic filtration law is then derived from the closure problem arising from the volume averaging method, proposing a new framework to understand the relationship between the effect of inertia on the macroscopic fluid-solid force and the topology of the microstructure of the porous medium. A second research axis is then investigated. As we deal with a deformable porous medium, we study the effect of the pore-scale fluid-structure interaction on the filtration law as the flow within the pores is unsteady, inducing time-dependent fluidstresses on the solid- phase. For that purpose, we implement pore-scale numerical simulations of unsteady flows within deformable pores, focusing for this preliminary study on a model porous medium. Owing to the large displacements of the solid phase, an immersed boundary approach is implemented. Two different numerical methods are compared to apply the no-slip condition at the fluid-solid interface: a diffuse interface approach and a sharp interface approach. The objective is to find the proper method to afford acceptable computational time and a good reliability of the results. The comparison allows a cross-validation of the numerical results, as the two methods compare well for our cases. This numerical campaign shows that the pore-scale deformation has a significant impact on the pressure drop at the macroscopic scale. Some fundamental issues are then discussed, such as the size of a representative computational domain or the form of macroscopic equations to describe the momentum transport within a soft deformable porous medium
2
Nagarajan, Ramakrishnan. "Micro-macroscopic modeling and simulation of an Automated Highway System." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10022008-063143/.
3
Zhou, Yi. "The macroscopic fundamental diagram in urban network: analytical theory and simulation." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49111.
Abstract:
The Macroscopic Fundamental Diagram (MFD) is a diagram that presents a relationship between the average flow (production) and the average density in an urban network. Ever since the existence of low scatter MFD in urban road network was verified, significant efforts have been made to describe the MFD quantitatively. Due to the complexity of the traffic environment in urban networks, an accurate and explicit expression for the MFD is not yet developed and many recent research efforts for MFD rely on computer simulations. On a single corridor, an analytical approximation model for the MFD exists. However, this thesis expanded this theory in two directions. First, we specialize the method for models with equal road length on the corridor, which greatly reduces the complexity of the method. We introduce the adoption of seven straight cuts in approximation. Computer simulations are conducted and show a high compatibility with the approximated results. However the analytical approximation can only be applied with the assumption of constant circulating vehicles in the system without turnings and endogenous traffics. Secondly, we show that turnings and endogenous traffic can bring various impact on the shape of the MFD, the capacity, the critical density, the variance in density and cause a phenomenon of clustered traffic status along the MFD curve. Furthermore, the simulation using stochastic variables reveals that the variance in turning rates and endogenous traffic don’t have significant impact on the MFD. This discovery enables studies to focus on scenarios with deterministic parameters for those factors. While traditional objective of engineering for network is to maximize capacity and widen the range for the maximum capacity, our results indicate that traffic stability at the maximum performance is poor if the system does not stay constantly in equilibrium status. This thesis provides insights into the factors that affect the shape of the MFD by analytical approximation and simulation.
4
De, Nicola Carmine. "Simulation and optimization of supply chains and networks using a macroscopic approach." Doctoral thesis, Universita degli studi di Salerno, 2011. http://hdl.handle.net/10556/172.
Abstract:
2009 - 2010The aim of thesis is to present some macroscopic models for supply chains and networks able to reproduce the goods dynamics, successively to show, via simulations, some phenomena appearing in planning and managing such systems and, nally, to deal with optimization problems. Depending on the observation scale supply networks modeling is charac- terized by di¤erent mathematical approaches: discrete event simulations and continuous models. Since discrete event models (Daganzo 2003) are based on considerations of individual parts, their main drawback is, however, an enor- mous computational e¤ort. Then a cost-e¤ective alternative to them is continu- ous models, described by some partial di¤erential equation. The rst proposed continuous models date back to the early 60 s and started with the work of Baumol (1970) and Forrester (1964), but the most signi cant in this direction was Daganzo (1997), where the authors, via a limit procedure on the number of parts and suppliers, have obtained a conservation law (Armbruster-Marthaler- Ringhofer 2004, Dafermos 1999), whose ux involves either the parts density or the maximal productive capacity. Then, in recent years continuous and homogenous product ow models have been introduced and they have been built in close connection to other transport problems like vehicular tra¢ c ow and queuing theory. Extensions on networks have been also treated. In this work, starting by the historical model of Armbruster - Degond - Ringhofer, we have compared two di¤erent macroscopic models, i.e. the Klar model, based on a di¤erential partial equation for density and an ordinary dif- ferential equation to capture the evolution of queues, and a continuum-discrete model, formed by a conservation law for the density and an evolution equa- tion for processing rate. Both the models can be applied for supply chains and networks. Moreover, an optimization problem of sequential supply chains modeled by the Klar approach has been treated. The aim is to nd the con guration of pro- duction according to the supply demand minimizing the queues length, i.e. the costs of inventory, and obtaining an expected pre-assigned out ow. The control problem is solved introducing and minimizing a cost functional which takes into account the nal ux of production and the queues representing the stores. The functional is not linear, so to nd its minimum, the vectors tangent method is introduced. This technique is based on the choice of an input ow which is a piecewise constant function, with a nite number of discontinuities. Considering on each of them an in nitesimal displacement which generates traveling tempo- ral shifts on processors and shifts on queues, we are able to compute numerically the value of the variation of functional respect to each discontinuities. Finally, we use the steepest-descent algorithm to nd, via simulations, the optimal con- guration of input ow, according to the pre- xed desired production. [edited by the author]
IX n.s.
5
Bart, Graeme. "Bridging the Microscopic and Macroscopic Realms of Laser Driven Plasma Dynamics." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38187.
Abstract:
The physical processes shaping laser plasma dynamics take place on length scales ranging from the microscopic (1 ångström) to the macroscopic realms (µm). Microscopic field fluctuations due to the motions of individual plasma charges evolve on an atomic scale. Collisional effects influencing thermalization and ionization processes depend on the plasma fields on an atomic level. Simultaneously, collective processes such as plasma oscillations take place on a mesoscopic length scale of many-nm. The macroscopic realm is ultimately determined by the laser which typically spans hundreds of nm to a few µm.
Consequently, ab-initio modelling of laser plasma dynamics requires the resolution of length scales from 1Å to multiple µm. As such, in order to bridge the microscopic and macroscopic length scales of light-matter interaction, in is necessary to account for the individual motions of up to ~10^11 particles. This is a not an insignificant undertaking.
Until recently, approaches to numerical modelling of light-matter interactions were limited to MD and PIC, each with their own limitations. MicPIC has been developed to fill the gap left by MD and PIC but so far has not been adapted for scalable parallel processing on large distributed memory machines. Thus, its full potential was not able to be fully realized until now.
This thesis presents the massively parallel MicPIC method capable of bridging the micro- and macroscopic realms. A wide range of applications that have heretofore not been accessible to theory or, at best, had limited applicability are now open for thorough investigation. Among these are nonlinear nanophotonics, quantum nanophotonics, laser machining, ab-initio dynamics of strongly coupled plasmas, high-harmonic generation, electron and x-ray sources, and optical switching. Two of the first applications of parallel MicPIC to a selection of such problems are shown and discussed below, demonstrating the applicability of the method to a wide variety of newly accessible strong field laser-plasma physics phenomena.
6
Mollier, Stéphane. "Two-dimensional macroscopic models for large scale traffic networks." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALT005.
Abstract:
Les fréquentes congestions que connaissent les réseaux routiers des grandes métropoles mondiales ont de lourdes conséquences économiques et environnementales. La compréhension et la modélisation dynamique des mécanismes à l'origine de ces congestions permettent d'en prédire l'évolution et donc d'améliorer l'efficacité des politiques de régulations utilisées par les opérateurs du réseau.La modélisation des réseaux routiers a commencé par le cas d'une route isolée puis a été étendue à des réseaux urbains. Ce changement d'échelle présente de nombreuses difficultés en matière de temps de calcul, de calibrage et de scénarisation, ce qui a incité la communauté scientifique à s'intéresser à des modèles agrégés, décrivant une représentation simplifiée de la réalité. Un de ces modèles vise à représenter de denses réseaux urbains par une équation aux dérivées partielles continue dans le plan. Ainsi, les véhicules sont représentés par une densité bi-dimensionnelle et leurs trajectoires sont décrites comme des directions de flux.L'objectif de la thèse est de développer cette approche et de proposer des méthodes pour son calibrage et sa validation. Les contributions correspondent à trois extensions successives du modèle. Tout d'abord, un simple modèle bi-dimensionnel est proposé pour le cas de réseaux homogènes --avec des limitations de vitesse et des concentrations de routes similaires en tout point-- et dans lesquels une direction de propagation privilégiée existe. Une méthode de comparaison avec un microsimulateur est présentée. Ensuite, le modèle est étendu au cas de réseaux hétérogènes --avec des limitations de vitesse et des concentrations de routes variables-- mais toujours avec une direction privilégiée. Ces dépendances spatiales permettent de décrire les phénomènes d'engorgement existant dans les réseaux routiers. Enfin, un modèle constitué de plusieurs couches, chacune représentant une direction de flux différente, est étudié. La complexité de la modélisation réside dans la formulation des interactions entre les différentes directions. Ce type de modèle n'est pas toujours hyperbolique ce qui impacte sa stabilitéCongestion in traffic networks is a common issue in big cities and has considerable economic and environmental impacts. Traffic policies and real-time network management can reduce congestion using prediction of dynamical modeling. Initially, researchers studied traffic flow on a single road and then, they extended it to a network of roads. However, large-scale networks present challenges in terms of computation time and parameters' calibration. This led the researchers to focus on aggregated models and to look for a good balance between accuracy and practicality.One of the approaches describes traffic evolution with a continuous partial differential equation on a 2D-plane. Vehicles are represented by a two-dimensional density and their propagation is described by the flow direction. The thesis aims to develop these models and devises methods for their calibration and their validation. The contributions follow three extensions of the model.First, a simple model in two-dimensional space to describe a homogeneous network with a preferred direction of flow propagation is considered. A homogeneous network has the same speed limits and a similar concentration of roads everywhere. A method for validation using GPS probes from microsimulation is provided. Then, a space-dependent extension to describe a heterogeneous network with a preferred direction of flow propagation is presented. A heterogeneous network has different speed limits and a variable concentration of roads. Such networks are of interest because they can show how bottleneck affects traffic dynamics. Finally, the case of multiple directions of flow is considered using multiple layers of density, each layer representing a different flow direction. Due to the interaction between layers, these models are not always hyperbolic which can impact their stability
7
Schurig, Michael. "The Vertex effect in polycrystalline materials simulation, a macroscopic model, and structural application /." [S.l.] : [s.n.], 2006. http://diglib.uni-magdeburg.de/Dissertationen/2006/micschurig.htm.
8
Dietrich, Sascha, H. Schulz, K. Hauch, K. Schladitz, M. Godehardt, J. Orlik, and D. Neusius. "3D Image Based Structural Analysis of Leather for Macroscopic Structure- Property Simulation - 226." Verein für Gerberei-Chemie und -Technik e. V, 2019. https://slub.qucosa.de/id/qucosa%3A34193.
Abstract:
Content:
The intrinsic structure significantly influences the mechanical properties of leather. In consequence, knowledge of leather’s hierarchical structure is essential in order to find the most suited leather for specific
application. Leather structure based parameters are of major importance for both manufacturing and leather processing industries. In this respect, intensive structure investigations have been subjected in
continuous research work.
Quantitative image analysis combined with stochastic micro-structure modelling and numerical simulation of macroscopic properties is a promising approach to gain a deeper understanding of complex relations between material’s micro-structure geometry and macroscopic properties. Key ingredient is a reliable geometric description provided by the quantitative analysis of 3D images of the material micro-structures. For leather, both imaging and image analysis are particularly challenging, due to the multi-scale nature of the leather’s micro-structure. Scales in leather are not well separated. Previously, high resolution computed tomography allowed 3D imaging of purely vegetable tanned leather samples at micro- and submicro- scale. Segmentation of leather structure as well as of typical structural elements in resulting image data is however hampered by a strong heterogeneity caused by lower scale structural information.
The first method for automatic segmentation of typical structural elements at varying scales combined morphological smoothing with defining and iteratively coarsening regions using the waterfall algorithm on
local orientations. It yields a hierarchical segmentation of the leather into coarse and fine structural elements that can be used to analyze and compare the structure of leather samples. Size and shape of the
structural elements as well as their sub-structure yield information, e. g. on undulation, branching, thickness, cross-sectional shape, and preferred directions.
In order to compare the micro-structure of leather samples from various body parts or even species, the segmentation has to be applicable without extensive pre-processing and parameter tuning. Robustness can be gained by applying smoothing methods that are adapted to the goal of defining image regions by similar local orientation. The challenge is that the space of fiber orientations in 3D is not equipped with an order. Motivated by a recent approach for nevertheless defining erosion and dilation on the sphere, we suggest new definitions for these morphological base transformations on the space of directions in 3D. We present segmentation results for 3D images of leather samples derived by these new morphological smoothing methods.
Take-Away:
The intrinsic structure significantly influences the mechanical properties of leather.
Leather’s hierarchical structure can be analyzed by quantitative 3D image analysis combined with stochastic micro-structure modelling.
Segmentation results for 3D images of leather samples derived by new morphological smoothing methods.
9
Reynolds, William Leonard. "Sustainable Service Rate Analysis at Signalized Intersections with Short Left Turn Pockets Using Macroscopic Simulation." NCSU, 2010. http://www.lib.ncsu.edu/theses/available/etd-03302010-171706/.
Abstract:
A macroscopic simulation tool is developed and tested in order to quantify the effects of short turn pockets on the sustainable service rate of a signalized intersection. Unlike the theoretical signal capacity, the sustainable service rate includes queue interaction effects and is thus influenced by blockage and spillback at the entrance to a short turn pocket. Previous research on the topic has focused either on the probability of spillback from a short turn pocket or the operation of a system with a single approach lane. No macroscopic model currently available has the ability to analyze throughput reductions due to short turn pocket effects on a multilane approach. The model described herein utilizes a series of flow and density restrictions on cells of varying sizes on the approach to the intersection. Results indicate sensitivity of the model to turn pocket spillback, blockage, saturation flow rate, pocket length, lane utilization, phase sequence, phase overlap, permitted phasing, and time-dependent demand. A phase optimization procedure is also described to help efficiently allocate green time for a given set of turn pocket lengths and turn movement percentages. Outputs from the model compare favorably to results generated using microsimulation software, and recommendations are made regarding additional model enhancements and testing needs.
10
Hildebrand, Cisilia, and Stina Hörtin. "A comparative study between Emme and Visum with respect to public transport assignment." Thesis, Linköpings universitet, Kommunikations- och transportsystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-112783.
Abstract:
Macroscopic traffic simulations are widely used in the world in order to provide assistance in the traffic infrastructure development as well as for the strategic traffic planning. When studying a large traffic network macroscopic traffic simulation can be used to model current and future traffic situations. The two most common software used for traffic simulation in Sweden today are Emme and Visum, developed by INRO respective PTV. The aim of the thesis is to perform a comparison between the software Emme and Visum with respect to the assignment of public transport, in other words how passengers choose their routes on the existing public transport lines. However, in order to make a complete software comparison the run-time, analysis capabilities, multi-modality, capacity to model various behavioural phenomena like crowding, fares etc. this will not be done in this comparison. It is of interest to study the differences between the two software algorithms and why they might occur because the Swedish Transport Administration uses Emme and the Traffic Administration in Stockholm uses Visum when planning public transport. The comparison will include the resulting volumes on transit lines, travel times, flow through specific nodes, number of boarding, auxiliary volumes and number of transits. The goal of this work is to answer the following objective: What are the differences with modelling a public transport network in Emme and in Visum, based on that the passengers only have information about the travel times and the line frequency, and why does the differences occur? In order to evaluate how the algorithms work in a larger network, Nacka municipality (in Stockholm) and the new metro route between Nacka Forum and Kungsträdgården have been used. The motivation for choosing this area and case is due to that it is interesting to see what differences could occur between the programs when there is a major change in the traffic network. The network of Nacka, and parts of Stockholm City, has been developed from an existing road network of Sweden and then restricted by "cutting out" the area of interest and then removing all public transportation lines outside the selected area. The OD-matrix was also limited and in order not to loose the correct flow of travellers portal zones was used to collect and retain volumes. To find out why the differences occur the headway-based algorithms in each software were studied carefully. An example of a small and simple network (consisting of only a start and end node) has been used to demonstrate and show how the algorithms work and why volumes split differently on the existing transit lines in Emme and Visum. The limited network of Nacka shows how the different software may produce different results in a larger public transport network. The results show that there are differences between the program algorithms but the significance varies depending on which output is being studied and the size of the network. The Visum algorithm results in more total boardings, i.e. more passengers have an optimal strategy including a transit. The algorithms are very similar in both software programs, since they include more or less parts of the optimal strategy. The parameters used are taken more or less into consideration in Emme and Visum. For example Visum will first of all focus on the shortest total travel time and then consider the other lines with respect to the maximum waiting time. Emme however, first focuses on the shortest travel time and then considers the total travel time for other lines with half the waiting time instead of the maximum wait time. This results in that less transit lines will be attractive in Emme compared to Visum. The thesis concludes that varying the parameters for public transport in each software algorithm one can obtain similar results, which implies that it is most important to choose the best parameter values and not to choose the "best" software when simulating a traffic network.
11
Grieshammer, Steffen Paul [Verfasser], Manfred [Akademischer Betreuer] Martin, and Michael [Akademischer Betreuer] Schroeder. "Atomistic and macroscopic simulation of solid oxide electrolytes and electrolyzer cells / Steffen Paul Grieshammer ; Manfred Martin, Michael Schroeder." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1128731126/34.
12
Grieshammer, Steffen [Verfasser], Manfred [Akademischer Betreuer] Martin, and Michael [Akademischer Betreuer] Schroeder. "Atomistic and macroscopic simulation of solid oxide electrolytes and electrolyzer cells / Steffen Paul Grieshammer ; Manfred Martin, Michael Schroeder." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://nbn-resolving.de/urn:nbn:de:hbz:82-rwth-2015-040481.
13
Lancaster, Joseph Paul Jr. "Predicting the behavior of robotic swarms in discrete simulation." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/18980.
Abstract:
Doctor of PhilosophyDepartment of Computing and Information Sciences
David Gustafson
We use probabilistic graphs to predict the location of swarms over 100 steps in simulations in grid worlds. One graph can be used to make predictions for worlds of different dimensions. The worlds are constructed from a single 5x5 square pattern, each square of which may be either unoccupied or occupied by an obstacle or a target. Simulated robots move through the worlds avoiding the obstacles and tagging the targets. The interactions between the robots and the robots and the environment lead to behavior that, even in deterministic simulations, can be difficult to anticipate. The graphs capture the local rate and direction of swarm movement through the pattern. The graphs are used to create a transition matrix, which along with an occupancy matrix, can be used to predict the occupancy in the patterns in the 100 steps using 100 matrix multiplications. In the future, the graphs could be used to predict the movement of physical swarms though patterned environments such as city blocks in applications such as disaster response search and rescue. The predictions could assist in the design and deployment of such swarms and help rule out undesirable behavior.
14
Mallach, Annegret, Frank Härtel, Frieder Heieck, Jan-Philipp Fuhr, Peter Middendorf, and Maik Gude. "Experimental comparison of a macroscopic draping simulation for dry non-crimp fabric preforming on a complex geometry by means of optical measurement." Sage, 2017. https://tud.qucosa.de/id/qucosa%3A35794.
Abstract:
Scope of the presented work is a detailed comparison of a macroscopic draping model with real fibre architecture on a complex non-crimp-fabric preform using a new robot-based optical measurement system. By means of a preliminary analytical process design approach, a preforming test centre is set up to manufacture dry non-crimp-fabric preforms. A variable blank holder setup is used to investigate the effect of different process parameters on the fibre architecture.The real fibre architecture of those preforms is captured by the optical measurement system, which generates a threedimensional model containing information about the fibre orientation along the entire surface of the preform. The measured and calculated fiber orientations are then compared with the simulation results in a three-dimensional overlay file. The results show that the analytical approach is able to predict local hot spots with high shear angles on the preform. Macroscopic simulations show a higher sensitivity towards changes in blank holder pressure than reality and limit the approach to precisely predict fibre architecture parameters on complex geometries.
15
Misic, Boris [Verfasser], Uwe [Akademischer Betreuer] Rau, and Jürgen H. [Akademischer Betreuer] Werner. "Analysis and simulation of macroscopic defects in Cu(In,Ga)Se2 photovoltaic thin film modules / Boris Misic ; Uwe Rau, Jürgen H. Werner." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1130326608/34.
16
Misic, Boris Verfasser], Uwe [Akademischer Betreuer] [Rau, and Jürgen H. [Akademischer Betreuer] Werner. "Analysis and simulation of macroscopic defects in Cu(In,Ga)Se2 photovoltaic thin film modules / Boris Misic ; Uwe Rau, Jürgen H. Werner." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1130326608/34.
17
Farzaneh, Mohamadreza. "Modeling Traffic Dispersion." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29757.
Abstract:
The dissertation studies traffic dispersion modeling in four parts. In the first part, the dissertation focuses on the Robertson platoon dispersion model which is the most widely used platoon dispersion model. The dissertation demonstrates the importance of the Yu and Van Aerde calibration procedure for the commonly accepted Robertson platoon dispersion model, which is implemented in the TRANSYT software. It demonstrates that the formulation results in an estimated downstream cyclic profile with a margin of error that increases as the size of the time step increases. In an attempt to address this shortcoming, the thesis proposes the use of three enhanced geometric distribution formulations that explicitly account for the time-step size within the modeling process. The proposed models are validated against field and simulated data.
The second part focuses on implementation of the Robertson model inside the popular TRANSYT software. The dissertation first shows the importance of calibrating the recurrence platoon dispersion model. It is then demonstrated that the value of the travel time factor β is critical in estimating appropriate signal-timing plans. Alternatively, the dissertation demonstrates that the value of the platoon dispersion factor α does not significantly affect the estimated downstream cyclic flow profile; therefore, a unique value of α provides the necessary precision. Unfortunately, the TRANSYT software only allows the user to calibrate the platoon dispersion factor but does not allow the user to calibrate the travel time factor. In an attempt to address this shortcoming, the document proposes a formulation using the basic properties of the recurrence relationship to enable the user to control the travel time factor indirectly by altering the link average travel time.
In the third part of the dissertation, a more general study of platoon dispersion models is presented. The main objective of this part is to evaluate the effect of the underlying travel time distribution on the accuracy and efficiency of platoon dispersion models, through qualitative and quantitative analyses. Since the data used in this study are generated by the INTEGRATION microsimulator, the document first describes the ability of INTEGRATION in generating realistic traffic dispersion effects. The dissertation then uses the microsimulator generated data to evaluate the prediction precision and performance of seven different platoon dispersion models, as well as the effect of different traffic control characteristics on the important efficiency measures used in traffic engineering. The results demonstrate that in terms of prediction accuracy the resulting flow profiles from all the models are very close, and only the geometric distribution of travel times gives higher fit error than others. It also indicates that for all the models the prediction accuracy declines as the travel distance increases, with the flow profiles approaching normality. In terms of efficiency, the travel time distribution has minimum effect on the offset selection and resulting delay. The study also demonstrates that the efficiency is affected more by the distance of travel than the travel time distribution.
Finally, in the fourth part of the dissertation, platoon dispersion is studied from a microscopic standpoint. From this perspective traffic dispersion is modeled as differences in desired speed selection, or speed variability. The dissertation first investigates the corresponding steady-state behavior of the car-following models used in popular commercially available traffic microsimulation software and classifies them based on their steady-state characteristics in the uncongested regime. It is illustrated that with one exception, INTEGRATION which uses the Van Aerde car-following model, all the software assume that the desired speed in the uncongested regime is insensitive to traffic conditions. The document then addresses the effect of speed variability on the steady-state characteristics of the car-following models. It is shown that speed variability has significant influence on the speed-at-capacity and alters the behavior of the model in the uncongested regime. A method is proposed to effectively consider the influence of speed variability in the calibration process in order to control the steady-state behavior of the model. Finally, the effectiveness and validity of the proposed method is demonstrated through an example application.Ph. D.
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Tournez, Florian. "Du composant au conducteur dans la boucle de simulation pour le test de véhicules électriques hybrides." Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILN060.
Abstract:
L'électrification des véhicules joue un rôle essentiel dans la lutte contre le réchauffement climatique. En réponse à la croissance de plus en plus marquée des véhicules électrifiés sur le marché automobile mondial, de nouvelles technologies ont émergé pour satisfaire la demande. Les simulations Hardware-in-the-Loop de type Signal (S-HIL) et Puissance (P-HIL) sont déjà utilisées dans l'industrie automobile pour tester différents composants et sous-systèmes de nouvelle génération avant leur intégration dans le prototype final, mais leur potentiel reste sous-exploité. Afin de favoriser leur utilisation et d'améliorer la vitesse de développement de nouvelles méthodes simples et abordables doivent être mises en place.L'objectif de cette thèse est de proposer une méthode souple permettant de tester divers sous-systèmes électriques grâce à des simulations HIL de puissance classiques jusqu'au test avec le conducteur dans la boucle de simulation (DIL). Le concept de la simulation HIL distribuée est introduit en se basant sur l'utilisation d'un serveur délocalisé. Le serveur délocalisé correspond à un ordinateur virtuel situé dans un centre de données équipé du logiciel de simulation Amesim Simcenter. Le logiciel permet d'avoir accès à une bibliothèque de modèles en ligne permettant à l'utilisateur de coupler ses modèles ou ses sous-systèmes situés localement avec Amesim Simcenter afin de réaliser des simulations pures, du S-HIL ou du P-HIL. Une interface simple et flexible a été mise en place par l'intermédiaire de l'organisation des modèles avec le formalisme de la Représentation Energétique Macroscopique (REM). La simulation HIL distribuée a été réalisée dans le cadre du Projet H2020 PANDA pour améliorer l'insertion des véhicules électrifiés sur le marché automobile. Le second axe est de mettre en place une simulation DIL couplée simultanément à une simulation P-HIL tout en gardant la flexibilité d'utiliser des modèles sous une plateforme de simulation temps réel. De cette manière, il est possible de tester un sous-système de puissance tout en incluant un conducteur au travers d'un simulateur de conduite (DIL/P-HIL)Vehicle electrification plays a crucial role in the fight against climate change. In response to the increasingly pronounced growth of electrified vehicles in the global automotive market, new technologies have emerged to meet the demand. Hardware-in-the-Loop simulations, such as Signal (S-HIL) and Power (P-HIL), are already used in the automotive industry to test various components and next-generation subsystems before their integration into the final prototype, but their potential remains underutilized. To promote their use and enhance the speed of development, new and affordable methods need to be implemented.The objective of this thesis is to propose a flexible method for testing various electrical subsystems, ranging from traditional HIL simulations to Driver-in-the-Loop simulation (DIL). The concept of distributed HIL simulation is based on the use of a remote server. The remote server corresponds to a virtual computer located in a data center equipped with the Amesim Simcenter simulation software. The software provides access to an online library of models, allowing the user to couple their models or locally located subsystems with Amesim Simcenter to perform pure simulations, S-HIL, or P-HIL. A simple and flexible interface has been established through the organization of models using the Energetic Macroscopic Representation (EMR) formalism. Distributed HIL simulation was carried out as part of the H2020 PANDA Project to improve the integration of electrified vehicles into the automotive market. The second focus is to implement a DIL simulation coupled simultaneously with a P-HIL simulation while retaining the flexibility of using models in a real-time simulation platform. This approach enables the testing of a power subsystem while incorporating a driver through a driving simulator (DIL/P-HIL)
19
Wang, Jie. "Simulation macro-méso de la mise en forme de renforts tissés interlocks." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI075.
Abstract:
L’étape de mise en forme dans le procédé RTM est importante car elle influence fortement le comportement mécanique du composite en service. Pour mieux prédire l’apparition de défauts éventuels des matériaux composites, les méthodes numériques sont de plus en plus développées compte tenu de la durée et du coût des essais. Déformations et orientations des mèches à l’échelle mésoscopiques sont essentielles pour simuler l’écoulement de la résine dans l’étape d’injection. Etant donné le nombre d’éléments et les interactions complexes, il est difficile d’effectuer les simulations de formage pour toute la pièce du renfort à l’échelle mésoscopique. La présente thèse consiste à développer une méthode multiéchelle qui permet de relier les simulations macroscopiques des renforts et les modélisations mésoscopiques de VER (volume élémentaire représentatif) lors de la mise en forme. D’abord, les simulations numériques macroscopiques pour trois renforts tissés différents sont réalisées à l’aide d’une loi de comportement hyperélastique, par la méthode des éléments finis avec un schéma explicite dynamique. Ensuite, les modélisations géométriques de VER à l’échelle mésoscopique sont reconstituées sur la base des images de tomographie X. Les champs de déplacements-déformations mésoscopiques des renforts tissés sont déterminés à partir des résultats macroscopiques et de la position des mèches. Pour prendre en compte les effets locaux de glissements des mèches, deux approches de simulations mésoscopiques de VER sont développées. Finalement, les résultats numériques mésoscopiques sont comparés avec ceux expérimentauxThe forming stage in the RTM process is crucial because it strongly influences the mechanical behavior of composites in service. In order to better predict the appearance of possible defects of composite materials, numerical simulations are increasingly developed taking into account the duration and the cost of experiences. Deformations and orientations of yarns at the mesoscopic scale are essential to simulate the resin flow in the stage of injection. Given the number of elements and their complex interactions, it is difficult to conduct the shaping simulations for the entire reinforcement at this mesoscopic scale. This present thesis consists in developing a multiscale method that allows linking the macroscopic simulations of reinforcements and the mesoscopic modellings of RVE (representative volume element) during the forming process. Firstly, the numerical simulations for three different woven reinforcements at the macroscopic scale are carried out using an anisotropic hyperelastic constitutive law, by the finite element method with a dynamic explicit scheme. Then, the geometrical modelling of RVE at the mesoscopic scale are reconstituted based on the tomographic images. The mesoscopic displacement-deformation fields of woven reinforcements are determined from the macroscopic results and the position of the yarns. In order to take into consideration sliding effects of yarns, two approaches of mesoscopic simulations of RVE are developed. Finally, the mesoscopic numerical results are compared with the experimental results
20
Bilan, Martin. "Simulace silniční infrastruktury." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-218217.
Abstract:
This Master thesis was created as research for project GA 102/09/1897 Security in car traffic - BAD, which is i.a. considers testing of continuousness of traffic with dynamically updated navigation. Main goal of project is simulator of traffic infrastructure creation. Simulators are two. One of them evaluate trafiic flow on bigger network of roads and crossroads. Second one simulate behaviour of cars during passage of crossroads. In this project is as well parsed theory of traffic activity and mentioned theoretical principles on which are built both simulators.
21
Soussi, Hakim. "Modèle global et paramétrable, pour la gestion des foules d'agents en animation comportementale." Phd thesis, Université de Bourgogne, 2011. http://tel.archives-ouvertes.fr/tel-00762319.
Abstract:
Le réalisme d'une application traitant de l'animation comportementale de foules est fondé d'une part sur le rendu graphique des scènes produites par l'application, mais aussi sur le réalisme du comportement lui-même. C'est ce dernier point qui est notre objet d'étude. Le réalisme du comportement d'une foule est avant tout global (réalisme macroscopique) : elle doit avoir des propriétés statistiques (densité, dispersion, vitesse moyenne,...) proches de celles d'une foule réelle. Il est aussi local (réalisme microscopique), c'est-à-dire que les agents ou groupes d'agents doivent idéalement avoir des comportements proches de ceux des humains ou groupes humains pris pour référence, tout au moins dans le domaine d'application restreint considéré. L'objet de cette thèse est de proposer un modèle générique pour effectuer des simulations comportementales de foules, pour pouvoir satisfaire simultanément les deux types de réalisme macroscopique et microscopique et rendre compte de la plupart des types de foules (foules homogènes, groupes, collection d'agents). Pour ce faire, nous avons dégagé quelques principes simples et peu coûteux en ressources. Nous introduirons la notion de contexte (global, localisé, et propagateur). Les contextes globaux et localisés appliqués à un groupe d'agents tendent à leur donner un même comportement et constituent ainsi un moyen de contrôle global de ces acteurs (réalisme macroscopique). Le contexte propagateur donne un moyen de propagation d'informations entre les agents de la foule (communication). Les agents eux-mêmes sont dotés de tendances qui, en les différenciant dans un même contexte, leur donne une variété de comportements qui concourt au réalisme microscopique.
22
Liu, Yuchen. "Synthesis, structural characterization and electrochemical hydrogen storage properties of LaNi5 and La4MgNi19 alloys prepared by mechanical alloying." Electronic Thesis or Diss., Bourgogne Franche-Comté, 2024. http://www.theses.fr/2024UBFCA004.
Abstract:
Le monde d'aujourd'hui est confronté à l'épuisement imminent des combustibles fossiles et à de graves problèmes environnementaux, et il est urgent de trouver des sources d'énergie propres et renouvelables. L’énergie hydrogène, en tant que source d’énergie propre, est un candidat potentiel. Dans une économie de l’hydrogène basée sur l’hydrogène énergie, le stockage de l’hydrogène constitue le principal obstacle à son développement. Les hydrures métalliques ont attiré l'attention en raison de leur sécurité et de leurs propriétés élevées de stockage de l'hydrogène. La première génération d'alliage commercial de stockage d'hydrogène à base de LaNi5 présente d'excellentes performances de stockage d'hydrogène et a été largement utilisée dans divers domaines. Cependant, en raison de sa faible capacité de stockage d’hydrogène, il est difficile de répondre aux exigences de l’Union européenne en matière de matériaux de stockage d’hydrogène. Les scientifiques utilisent souvent une seule méthode d’optimisation, comme la substitution d’éléments, les nouvelles voies de synthèse, l’optimisation de surface, etc. Cependant, peu d’articles rapportent des méthodes d’optimisation combinant les deux méthodes.Dans ce travail, les premiers principes ont été utilisés pour sélectionner le meilleur élément Cr pour remplacer Ni. L'alliage mécanique a été utilisé pour synthétiser l'alliage LaNi5 et l'alliage LaNi4Cr. La micromorphologie et la composition des phases de différents échantillons produits avec différents paramètres de broyage à boulets ont été caractérisées par des tests SEM et XRD. Les performances de stockage de l'hydrogène de l'échantillon ont ensuite été testées, et les performances de stockage de l'hydrogène gazeux et les performances électrochimiques de l'échantillon ont été obtenues. Les propriétés de stockage de l'hydrogène de tous les échantillons ci-dessus sont comparées les unes aux autres et les résultats reflètent l'efficacité de la combinaison des méthodes d'alliage mécanique et de substitution d'éléments pour l'optimisation de LaNi5.De plus, une autre méthode d’optimisation de l’alliage LaNi5 a également été réalisée, à savoir sa combinaison avec la phase AB2 pour former l’alliage La4MgNi19. Un total de 6 ensembles de paramètres avec différents temps de broyage à billes et différents précurseurs ont été utilisés pour synthétiser l'alliage La4MgNi19. La composition des phases et les propriétés de stockage de l'hydrogène de tous les échantillons ont été obtenues et comparées aux propriétés de stockage de l'hydrogène de LaNi4Cr. Les résultats montrent que les performances de stockage de l'hydrogène de l'alliage La4MgNi19 sont meilleures que celles de l'alliage LaNi5, mais légèrement pires que celles de l'alliage LaNi4Cr.Enfin, à l’aide d’un logiciel de simulation, les paramètres de l’alliage LaNi4Cr ont été introduits dans le modèle éprouvé de réservoir de stockage d’hydrogène afin d’explorer les performances de cet alliage dans le réservoir de stockage d’hydrogène. Après avoir exploré les effets de différents paramètres sur le réservoir de stockage d’hydrogène, des conduites d’eau ont été ajoutées pour ajuster l’échange thermique. Les résultats montrent que les réservoirs de stockage d’hydrogène remplis de LaNi4Cr ont d’excellentes performancesToday's world is facing the imminent depletion of fossil fuels and serious environmental problems, and it is urgent to find clean and renewable energy sources. Hydrogen energy, as a clean energy source, is a potential candidate. In a hydrogen economy based on hydrogen energy, hydrogen storage is the biggest obstacle limiting its development. Metal hydrides have attracted attention due to their safety and high hydrogen storage properties. The first generation of commercial hydrogen storage alloy LaNi5-based alloy has excellent hydrogen storage performance and has been widely used in various fields. However, due to its low hydrogen storage capacity, it is difficult to meet the requires of the European Union for hydrogen storage materials. Scientists often use a single optimization method, such as element substitution, new synthetic routes, surface optimization, etc. However, few articles report optimization methods that combine the two methods.In this work, first principles were used to screen out the best element Cr to substitute Ni. Mechanical alloying was used to synthesize LaNi5 alloy and LaNi4Cr alloy. The micromorphology and phase composition of different samples produced with different ball milling parameters were characterized by SEM and XRD tests. The hydrogen storage performance of the sample was then tested, and the gaseous hydrogen storage performance and electrochemical performance of the sample were obtained. The hydrogen storage properties of all the above samples are compared with each other, and the results reflect the effectiveness of the combination of mechanical alloying and element substitution methods for the optimization of LaNi5.In addition, another optimization method of LaNi5 alloy was also carried out, that is, combining it with AB2 phase to form La4MgNi19 alloy. A total of 6 sets of parameters with different ball milling times and different precursors were used to synthesize La4MgNi19 alloy. The phase composition and hydrogen storage properties of all samples were obtained and compared with the hydrogen storage properties of LaNi4Cr. The results show that the hydrogen storage performance of La4MgNi19 alloy is better than that of LaNi5 alloy, but slightly worse than that of LaNi4Cr alloy.Finally, with the help of simulation software, the parameters of the LaNi4Cr alloy were introduced into the proven hydrogen storage tank model to explore the performance of this alloy in the hydrogen storage tank. After exploring the effects of different parameters on the hydrogen storage tank, water pipes were added to adjust the heat exchange. The results show that hydrogen storage tanks filled with LaNi4Cr have excellent performance
23
Lätzel, Marc. "From microscopic simulations towards a macroscopic description of granular media." [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10447201.
24
Orliac, Jean-Guillaume. "Analyse et simulation du comportement anisotrope lors de la mise en forme de renforts tissés interlock." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00823359.
Abstract:
Afin de pouvoir prédire le comportement des renforts de composites 3D interlock au cours d'un procédé de mise en forme, il est nécessaire de connaitre la position des mèches dans le renfort durant la phase de préformage du procédé. Les travaux présentés ici traitent de la simulation du préformage de renforts 3D épais à l'aide d'un élément fini hexaédrique semi-discret spécifique. En utilisant le principe des travaux virtuels, on distingue le travail interne virtuel dû à la tension des mèches des autres travaux virtuels. La raideur due aux tensions de mèches, qui constitue la contribution principale de la rigidité du matériau, est prise en compte à l'aide de barres incluses dans les éléments. Les rigidités dues aux autres sollicitations, comme la compression transverse, les cisaillements ou les frottements inter-mèches, sont décrites par un matériau continu additionnel. La combinaison de ce modèle discret du premier ordre et d'un matériau continu hyperélastique anisotrope dit du second ordre, pour formuler le comportement du matériau va permettre la simulation du préformage des renforts tissés épais. Conjointement aux travaux sur la simulation, des travaux expérimentaux pour l'identification des paramètres matériau de la loi de comportement ont été définis et réalisés. Ces paramètres concernent les deux parties de la formulation du comportement.
25
Ni, Daiheng. "Extension and generalization of Newell's simplified theory of kinematic waves." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-11112004-112805/unrestricted/ni%5Fdaiheng%5F200412%5Fphd.pdf.
Abstract:
Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2005.Leonard, John D., Committee Chair ; Goldsman, Dave, Committee Member ; Amekudzi, Adjo, Committee Member ; Hunter, Michael, Committee Member ; Dixon, Karen, Committee Member. Vita. Includes bibliographical references.
26
Jiao, Jianwu. "Microscopic and macroscopic cellular-automaton simulations of fluid flow and wave propagation in rocks." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23995.pdf.
27
Aviziotis, Ioannis. "Chemical vapor deposition of Al, Fe and of the Al13Fe4 approximant intermetallic phase : experiments and multiscale simulations." Thesis, Toulouse, INPT, 2016. http://www.theses.fr/2016INPT0100/document.
Abstract:
Des couches minces contenant des phases intermétalliques présent et des propriétés et de combinaisons de propriétés qui ne sont que partiellement explorées. Elles portent des solutions potentielles pour conférer des multifonctionnalités à des matériaux avancés requis par les secteurs industriels et sont source derupture et de l'innovation. Leur élaboration par dépôt chimique en phase vapeur à partir de précurseurs métallo-organiques (MOCVD) permet un dépôt conforme sur, et la fonctionnalisation de surfaces complexes, avec un temps de traitement court et à un coût modéré.Pour ceci, il est nécessaire de contrôler les réactions chimiques complexes et des mécanismes de transport impliqués. La modélisation informatique du procédé, alimentée avec des données obtenues par des expériences de dépôt ciblées, est un outil intégré pour l'étude et la compréhension des phénomènes qui se produisent à différentes échelles,de l’échelle macroscopique à celle nanométrique. La MOCVD de composés intermétalliques Al-Fe est étudiée en tant que paradigme de la mise en oeuvre d'une telle approche combinée, expérimentale et théorique. La phase approximanteAl13Fe4 est particulièrement ciblée,en raison de son intérêt comme alternative peu onéreuse aux catalyseurs à base de métaux noble dans l'industrie chimique. La mise au point du dépôt de la phase Al13Fe4est subordonnée à l'étude des proc /min à 185oC. La simulation du procédé prédit des vitesses de croissance en bon accord avec ces résultats, en particulier dans la gamme 139oC-227oC. La modélisation multi-échelle prédit la rugosité RMS avec précision, permettant ainsi le contrôle des propriétés telles que la résistivité électrique. La possibilité d'obtenir des films MOCVD de Fe à faible contamination en O et C est explorée dans la gamme 130oC-250oC à partir de fer pentacarbonyle, Fe(CO)5. La morphologie de la surface des films dépend fortement de la température de dépôt; elle devient plus lisse au-dessus de200oC, qui correspond aussi à la vitesse de croissance maximale, 60nm/min. La vitesse de dépôt diminue fortement lorsque la pression augmente. Les prédictions de la modélisation macroscopique reproduisent précisément ce comportement. Elles indiquent que la diminution de la vitesse de croissance à des températures et des pressions élevées est due à l’augmentation de la décomposition du précurseur en phase gazeuse et à l'inhibition de la réactivité de surface par le ligand CO. Le modèle multi échelle conduit à des valeurs RMS en bon accord avec les mesures expérimentales, en particulier à des températures plus élevées. Suite à l’étude des deux procédés, des co-dépôts d'Al-Fe effectués à 200oCrésultent en des films riches en Alavec une microstructure poreuse et rugueuse. Ceux-ci ne contiennent pas de phases intermétalliques et sont riches en oxygène dû à la réaction d'Al avec les ligandscarbonyles. Afin d’éliminer la contamination, des dépôts séquentiels d'Al et de Fe sont réalisés, ce dernier dans des conditions modifiées à 140oC, 40Torr et 10 min. Ces films sont exemptes d’hétéroélements et présentent un rapport atomique Al:Fe13:4. Diffraction des rayons X et microscopies électroniques révèlent qu’un recuit in situ à 575oC pendant 1 h conduit à des films à gradient de la composition sur l'épaisseur,composés de la phase approximantem-Al13Fe4 conjointement avec des phases intermétalliques Al-Fesecondaires. Il est ainsi démontré que des procédés MOCVD sont appropriés pour obtenir des films constitués d'alliages intermétalliques.Ces films multifonctionnels,appliqués de façon conforme sur des surfaces complexes sont utiles pour un grand nombre d'applicationsFilms containing intermetallic compounds exhibit properties and combination of properties which are only partially explored. They carry potential solutions to confer multifunctionality to advanced materials required by industrial sectors and to become a source of breakthrough and innovation.Metalorganic chemical vapor deposition (MOCVD) potentially allows conformal deposition on, and functionalization of complex surfaces, with high throughput and moderate cost. For this reason, it is necessary to control the complex chemical reactions and the transport mechanisms involved in a MOCVD process. In this perspective, computational modeling of the process, fed with experimental information from targeted deposition experiments, provides an integrated tool for the investigation and the understanding of the phenomena occurring at different length scales, from the macro- to the nanoscale. The MOCVD of Al-Fe intermetallic compounds is investigated in the present thesis as a paradigm of implementation of such a combined, experimental and theoretical approach. Processing of the approximant phase Al13Fe4 is particularly targeted, due to its potential interest as low-cost and environmentally benign alternative to noble metal catalysts in the chemical industry. The attainment of the targeted Al13Fe4 intermetallic phase passes through the investigation of the MOCVD of unary Al and Fe films. The MOCVD of Al from dimethylethylamine alane (DMEAA) in the range 139oC-241oC results in pure films. Increase of the deposition temperature yields higher film density and decreased roughness. The Aldeposition rate increases to a maximum of 15.5 nm/min at 185oC and then decreases. Macroscopic simulations of the process predictdeposition rates in sufficient agreement with experimental measurements, especially in the range 139oC-227oC. At higher temperatures, competitive gas phase and surface phenomena cannot be captured by the applied model. Multiscale modeling of the process predicts the RMS roughness of the films accurately, thus allowing the control of properties such as electrical resistivity which depend on the microstructure. The MOCVD of Fe from iron pentacarbonyl, Fe(CO)5, is investigated in the range 130oC-250oC for the possibility toobtain fairly pure Fe films with low Oand C contamination. The surface morphology depends strongly on the temperature and changes are observed above 200oC. The Fe deposition rate increases up to 200oC, to a maximum of 60 nm/min, and then decreases. Moreover, the deposition rate decreases sharply with increasing pressure. Computational predictions capture accurately the experimental behavior and they reveal that the decrease athigher temperatures and pressures is attributed to the high gas phase decomposition rate of the precursor and to inhibition of the surface fromCO. The multiscale model calculates RMS roughness in good agreement with experimental data, especially at higher temperatures. Upon investigation of the two processes, aseries of Al-Fe co-depositions performed at 200oC results in Al-rich films with a loose microstructure. They contain no intermetallic phases and they are O-contaminated due to the reaction of the Al with the carbonyl ligands. Sequential deposition of Al and Fe followed by in situ annealing at 575oC for 1 h is applied to bypass the Ocontamination. The process conditions of Fe are modified to 140oC, 40 Torr and 10 min resulting in O-free films with Al:Fe atomic ratio close to the targeted 13:4 one. Characterization techniques including X-ray diffraction, TEM and
28
Mariotte, Guilhem. "Dynamic Modeling of Large-Scale Urban Transportation Systems." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSET010/document.
Abstract:
La congestion en milieu urbain est un enjeu majeur que ce soit d’un point vue économique, social ou environnemental. À court et moyen terme, l’utilisation de la simulation dynamique du trafic routier peut permettre d’analyser et de guider des politiques d’optimisation des infrastructures existantes. Aujourd’hui, du fait de la complexité des systèmes de transport, les outils de modélisation classiques sont limités à des échelles géographiques peu étendues (de l’ordre du quartier). À grande échelle, le temps de calcul devient rapidement un facteur limitant tout comme le calibrage et la scénarisation. Néanmoins les dernières décennies ont vu l’apparition d’une nouvelle génération de modèles bien adaptés aux métropoles urbaines. Ceux-ci sont basés sur une relation phénoménologique entre la production de déplacements et le nombre de véhicules dans une zone spatiale d’un réseau routier, appelée Diagramme Fondamental de Zone (Macroscopic Fundamental Diagram, MFD). Cette relation, validée empiriquement sur de nombreuses villes, a permis d’étudier différentes méthodes de contrôle du trafic pour une ville entière, mais a été peu utilisée à des fins de prévision de la congestion. L’objectif de cette thèse est de proposer un premier outil opérationnel de simulation et d’analyse des grands réseaux de métropoles, en utilisant et développant les modèles de trafic basés sur la relation MFD. Cet outil doit posséder un cadre théorique cohérent qui puisse convenir à des applications telles que la prévision d’états de trafic, le développement de nouvelles politiques de contrôle, l’estimation de pollutions liées au trafic, etc. Les contributions de la thèse portent sur deux aspects. Le premier est l’analyse des propriétés mathématiques et physiques des modèles existants, en incluant une formalisation complète de la gestion de plusieurs longueurs de parcours au sein d’une même zone urbaine. En particulier, cette formalisation traite de la distinction des trajets internes à la zone et des problèmes de flux convergents et divergents pour les trajets traversant la zone lorsque la congestion se propage d’une zone à l’autre. Le deuxième aspect est la proposition d’un nouveau modèle basé sur la distance individuelle parcourue à l’intérieur d’une zone urbaine (trip-based). Cette approche permet d’individualiser les usagers (auparavant représentés sous forme de flux continus) et donc de définir plus finement leurs caractéristiques, en vue de coupler leurs déplacements à des modèles d’affectations sur différentes routes. Enfin, des exemples d’application illustrant diverses collaborations sont donnés en dernière partie de la thèse. La simulation du trafic sur l’aire urbaine du Grand Lyon (France) y est présentée, ainsi que de nouveaux modules de modélisation de la recherche de parking ou de contrôle périphérique. Cette thèse est partie intégrante d’un projet européen ERC intitulé MAGnUM : Approche multi-échelle et multimodale de la modélisation du trafic pour une gestion durable de la mobilité urbaineCongestion in urban areas has become a major issue in terms of economic, social or environmental impact. For short or mid term, using dynamic road traffic simulation can help analyzing and providing guidelines to optimization policies of existing infrastructures. Today, because of the complexity of transport systems, classical modeling tools are limited to small geographical areas (of a district size). Computational time, together with simulation calibration, are notably very constraining at large scales. However, a new generation of models designed for metropolitan areas has arisen over the past decades. These models are based on a phenomenological relationship between travel production and the number of vehicles in a given spatial area of a road network, known as the Macroscopic Fundamental Diagram (MFD). This relationship, supported by empirical evidences from several cities around the world, has allowed the study of different traffic control schemes at a whole city scale, but was rarely used for traffic state forecasting. The aim of this PhD is to propose an efficient modeling tool, based upon the concept of MFD, to simulate and analyze traffic states in large metropolitan areas. The theoretical framework of this tool must be consistent and applicable for traffic state forecasting, development of new control policies, traffic emission estimation, etc. There are two major contributions in this PhD. The first one is analyzing the mathematical and physical properties of existing models, and formalizing the dynamics of several trip lengths inside the same urban zone. In particular, this formalization distinguishes between internal trips and trips crossing the zone. Flow merging and diverging issues are also addressed when congestion propagates from one zone to another. The second contribution is proposing a new trip-based model based on individual traveled distance. This approach allows to treat users independently (previously represented with continuous flows), and thus to define their characteristics more precisely to couple their trips with assignment models on different paths. Finally, examples of application from various collaborations are given in the last part of this thesis. It includes a simulation study of the Grand Lyon urban area (France), as well as new modules to simulate search-for-parking or perimeter control. This PhD is part of a European ERC project entitled MAGnUM: Multiscale and Multimodal Traffic Modeling Approach for Sustainable Management of Urban Mobility
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Krebs, Isabel [Verfasser], Sibylle [Akademischer Betreuer] [Gutachter] Günter, and Katharina [Gutachter] Krischer. "3D nonlinear magnetohydrodynamic simulations of macroscopic internal instabilities in tokamak plasmas / Isabel Krebs ; Gutachter: Sibylle Günter, Katharina Krischer ; Betreuer: Sibylle Günter." München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1139493140/34.
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Vilfayeau, Jérôme. "Modélisation numérique du procédé de tissage des renforts fibreux pour matériaux composites." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0026/document.
Abstract:
L'industrie aéronautique doit faire face aux nouvelles exigences environnementales, tout particulièrement concernant la réduction de la consommation des énergies fossiles. L'utilisation de matériaux composites plus léger permet de répondre en partie à cette attente. Pour limiter les coûts lors de la fabrication et du développement des composites à renforts tissés 3D, il est nécessaire d'utiliser des outils de simulation performants. En particulier, les outils existants, qui discrétisent à une échelle mésoscopique l'architecture des tissus 3D, ne tiennent pas compte de l'influence du procédé de fabrication sur la constitution de la structure textile. Si des outils numériques dédiés à la modélisation du procédé de tressage et de tricotage sont disponibles, il n'en est rien concernant le tissage. Cette étude avait donc pour but de s'intéresser plus particulièrement à la simulation du prodécé de tissage pour pouvoir obtenir une structure de tissu sèche déformée numériquement. La production de différentes architectures de tissu en verre E dans notre laboratoire nous a permis d'observer les différents éléments en contact avec le fil ou le tissu sur la machine à tisser, par le biais de l'utilisation d'une caméra rapide par exemple. Le développement d'un modèle numérique par éléments finis reproduisant le procédé de tissage a été réalisé. Une loi de comportement isotrope transverse fut utilisée pour modéliser les fils de verre. Des premières simulations numériques encourageantes pour la fabrication d'un tissu d'armure toile et d'un tissu d'armure croisé 2-2 sont présentées et comparées avec les tissus réels produits correspondantsThe aeronautical industry faces new challenges regarding the reduction of fossil fuel consumption. One way to address this issue is to use lighter composite materials. The ability to predict the geometry and the mechanical properties of the unit cell is necessary in order to develop 3D reinforcements in composite materials for these aeronautical applications. There is a difficulty to get realistic geometries for these unit cells due to the complexity of their architecture. Currently, existing tools which model 3D fabrics at a meso scale don't take into account manufacturing process influence on the shape modification of the textile structure. There is already some numerical tools that can model the braiding or knitting process, but none have been developed for weaving so far. Consequently, this study deals with the numerical simulation of the weaving process to obtain a deformed dry fabric structure. During the weaving process of E-glass fabrics, achieved in our laboratory, it has been observed that large deformations led to the modification of transverse section of meshes, or local density changes, that can modify the fabrics mechanical resistance. For this reason, a numerical tool of the weaving process, based on finite element modelling, has been developped to predict these major deformations and their influences on the final textile structure. The correlation between numerical results and fabrics produced with glass fibres has been achieved for plain weave and 2-2 twill
31
Pessot, Giorgio [Verfasser]. "Coarse-Grained Discretized Description of Magneto-Responsive Elastomers: Mesoscopic Modeling as a Bridge Pillar between Microscopic Simulations and Macroscopic Behavior / Giorgio Pessot." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2018. http://d-nb.info/1150919965/34.
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Mouawad, Lena. "Monte Carlo simulations and a theoretical study of the damage induced by ionizing particles at the macroscopic scale as well as the molecular scale." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE009/document.
Abstract:
Le travail présenté dans cette thèse se place dans le contexte de la simulation de dommages biologiques. D'abord une étude macroscopique met en question la pertinence des plans de traitement basés sur la dose absorbée et le passage à une étude de micro-dosimétrie permet l'utilisation de paramètres biologiques plus pertinents, tels que les cassures de brins d'ADN. La validité des sections efficaces d'interaction sur lesquelles se basent ces simulations est discutée en plus de détails. Suite à la complexité du milieu biologique, les sections efficaces d'interaction avec l'eau sont souvent utilisées. Nous développons un algorithme qui permet de fournir les sections efficaces d'ionisation pour n'importe quelle cible moléculaire, en utilisant des outils qui permettent de surmonter les difficultés de calcul, ce qui rend notre programme particulièrement intéressant pour les molécules complexes. Nous fournissons des résultats pour l'eau, l'ammoniac, l'acide formique et le tétrahydrofuraneThe work presented in this thesis can be placed in the context of biological damage simulation. Webegin with a macroscopic study where we question the relevance of absorbed-dose-based treatmentplanning. Then we move on to a micro-dosimetry study where we suggest the use of morebiologically relevant probes for damage, such as DNA strand breaks. More focus is given to thefundamental considerations on which the simulations are based, particularly the interaction crosssections. Due to the complexity of the biological medium, the interaction cross sections with waterare often used to simulate the behavior of particles. We develop a parallel user-friendly algorithmthat can provide the ionization cross sections for any molecular target, making use of particular toolsthat allow to overcome the computational difficulties, which makes our program particularlyinteresting for complex molecules. We provide preliminary results for water, ammonia, formic acidand Tetrahydrofuran
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Tounsi, Rami. "Comportement des structures en nids d'abeilles sous sollicitations dynamiques mixtes compression/cisaillement et effet de l'orientation des cellules." Phd thesis, Université de Valenciennes et du Hainaut-Cambresis, 2014. http://tel.archives-ouvertes.fr/tel-01002421.
Abstract:
Les nids d'abeille d'aluminium combinent légèreté et grande capacité d'absorption d'énergie. Ils sont alors de plus en plus utilisés dans les secteurs du transport (automobile, aéronautique ...) pour contribuer conjointement à l'allègement structural et à la sécurité. Dans cette thèse, le comportement à l'écrasement des nids d'abeille est étudié en tenant compte de l'effet combiné de l'angle d'orientation dans le plan des cellules, de l'angle de chargement et de la vitesse de sollicitation, que la littérature ne relate pas. Un dispositif de chargement mixte compression/cisaillement est conçu pour mener l'étude expérimentale. L'analyse des résultats porte sur le pic initial d'effort, le plateau d'effort, ainsi que sur les modes de déformation. Les résultats montrent une augmentation de la résistance sous sollicitation dynamique dépendante de l'angle de chargement Ψ. Elle devient moins significative quand l'angle de chargement augmente jusqu'à atteindre un angle critique. Pour Ψ > Ψcritique, les réponses quasi-statiques sont même plus élevées que les réponses dynamiques. Une étude numérique est alors entreprise. Elle permet de comprendre ce phénomène qui est imputé aux mécanismes de déformation locaux des cellules. Les résultats numériques montrent également que l'effet de l'angle d'orientation □ dans le plan est plus prononcé sur la force tangentielle que sur la force normale, que cela influence également les modes d'effondrement et donc la réponse mécanique. Ces simulations numériques, couplées aux résultats expérimentaux, permettent alors de dissocier les composantes normale et tangentielle de la réponse des nids d'abeille et d'identifier les paramètres d'un critère macroscopique de résistance exprimé en fonction de la vitesse d'impact, de l'angle de chargement et de l'angle d'orientation dans le plan. Finalement, dans le but de réduire le coût des simulations numériques, un modèle élément fini (EF) réduit basé sur un critère de périodicité tenant compte de l'angle d'orientation dans le plan est proposé et son domaine de validité est évalué.
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Farrell, Troy W. "The mathematical modelling of primary alkaline battery cathodes." Thesis, Queensland University of Technology, 1998.
35
Roux, Patrick. "Modélisation de la solidification colonnaire et équiaxe de mélanges binaires." Paris 6, 2005. http://www.theses.fr/2005PA066630.
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Benezech, Jean. "Modélisation aux échelles méso- et macroscopique du comportement mécanique de zones singulières de pièces de structure en CMC." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0309.
Abstract:
Les composites à matrice céramique (CMC) présentent une architecture multi-échelle complexe. Pour être utilisé en tant que composant de moteur aéronautique qui nécessitent des géométries complexes, ces matériaux doivent être tissés sous forme d'architectures textiles spécifiques. Mon travail s’est concentré sur l’étude d’une pièce de type raidisseur, et plus particulièrement sur le détail d’une jonction composite tissée. La taille caractéristique de cette pièce se situe entre les échelles méso- et macroscopique, ce qui rend impossible l’utilisation des hypothèses de séparabilité des échelles. Nous avons tout d’abord développé un montage expérimentale de flexion/cisaillement adapté à la jonction tissée. Ces essais ont non seulement permis d’identifier et de caractériser le comportement mécanique de cette pièce, mais aussi, de mettre en lumière l’interdépendance entre le chargement, l’architecture textile et les mécanismes d’endommagement, qui est particulièrement importante dans le cas de la jonction tissée. C’est pourquoi, la modélisation de ce détail de structure doit inclure une connaissance approfondie de l’architecture interne du matériau. Nous avons donc développé une approche originale de segmentation variationnelle à partir de µCT, afin de construire des modèles numériques réalistes du matériau à l’échelle mésoscopique. Cette approche repose sur une heuristique globale-locale qui améliore itérativement la ressemblance d’un modèle géométrique initial. Cette démarche a permis de construire le jumeau numérique de la jonction tissée. Le modèle final ne comportant pas d’interpénétration entre fils, un maillage tétraédrique conforme peut ensuite être généré directement à partir de l’image ainsi labellisée. Des simulations EF à l’échelle mésoscopique ont été menées en prenant en compte le comportement non-linéaire des constituants des CMC. Elles permettent de prévoir le niveau de chargement menant aux premiers endommagements. De plus, la localisation des endommagements ainsi que leurs interactions avec l’architecture méso ont également ont été reproduites de manière satisfaisante.Cependant, ces modèles incluent une description très détaillée du matériau et nécessitent donc des ressources de calcul importantes. Une description approchée de ces détails pourrait être suffisante pour obtenir une prédiction correcte des propriétés élastiques, voir de l’amorçage de l’endommagement. Nous avons donc proposé un pont méso-macro permettant de construire le comportement apparent des éléments macroscopiques à partir de l’information méso sous-jacente. Les propriétés des éléments macroscopiques sont obtenues en assimilant localement le matériau à un stratifié équivalent construit à partir des fractions volumiques et des orientations locales des constituants. Cette approche permet de réduire drastiquement la taille des problèmes EF, tout en conservant une description approchée de la méso-structure. Le modèle macroscopique enrichi permet de reproduire fidèlement les résultats obtenus à l’échelle mésoscopique, tant que la taille de filtrage reste comparable à celle des fils.Les modèles proposés ont été utilisés pour reproduire les résultats expérimentaux et approfondir leur analyse. Nous avons étudié en particulier la sensibilité aux conditions aux limites de l’essai, ainsi que l’influence des variabilités liées au procédé de fabrication des éprouvettes. Enfin, la chaine d’outils développée dans le cadre de la thèse pourra être utilisée pour étudier différentes définitions textiles de la jonction, permettant in fine de définir l’architecture optimale de la pièceWoven ceramic matrix composites (CMC) exhibit an intricate multi-scale architecture. To be used as components of aircraft engines, the weaving of such parts could also incorporate specific features compared to « classical » woven CMC as they need to comply with complex geometries. My work focused on a stiffener-like fully woven junction that is made of a complex 3D woven fabric, and whose characteristic size lies at the frontier between the mesoscopic and the macroscopic scales, i.e. where scale separation hypothesis is not applicable.I have first developed an experimental device to perform shear/bending tests on the woven junction. These tests not only allowed to gain significant knowledge about the mechanical behavior of such part, but also to highlight the interplay between the load, material architecture and damage mechanisms that is particularly significant in the case of the woven junction. Therefore, numerical prediction of the mechanical behavior of the woven junction necessitates a sound knowledge of its inner structure.With this aim, I have developed an original segmentation method to build realistic numerical models of textile composites, using X-ray micro-computed tomography and a prior geometric model. The procedure includes a global-local heuristic to iteratively improve the resemblance of the initial model. This approach allowed to build “digital twins” of the woven junction. A conformal tetrahedral image-based mesh could then be obtained as the resulting models are free of interpenetration. Mesoscale FE simulations, including non-linear behavior laws of the yarns and matrix, allowed to predict the maximal load leading to the first damage events, and to reproduce accurately the damage localization and its interaction with the architecture.However, with such level of details incorporated in the model, the simulations necessitate significant computational resources. An approximate macro-scale description may be sufficient to evaluate the elastic properties, or even to simulate damage initiation. Therefore, we have proposed a meso-informed macroscopic modelling framework where the behaviour of the macro-elements is derived from the knowledge of the local direction and volume fraction of constituents, thanks to the digital twin. The effective behaviour of the macro-elements is obtained through an equivalent lamina. This method drastically reduces the size of the model while preserving an approximate description of the underlying local anisotropy and heterogeneities. With respect to the damage initiation, the meso-informed macroscopic model accurately reproduced the results obtained using the reference mesoscale model, as long as the filtering size remains comparable to the yarn size. This allowed to propose an optimal modelling framework with an adequate level of description of meso-details and acceptable computational requirements.Finally, I have used these models to thoroughly compare the numerical simulations with the experimental results: variabilities of experimental boundary conditions have been analyzed, as well as the influence of specific heterogeneities related to the fabrication process. We have also used this framework to explore different weaving patterns in order to obtain an optimal design of the woven junction
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Teruel, Federico E. "Macroscopic turbulence modeling and simulation for flow through porous media /." 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3301234.
Abstract:
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1302. Adviser: Rizwan Uddin. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.
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(8791256), Michael J. Garee. "Complexity measurement of macroscopic opinion dynamics to infer mechanisms within social influence networks." Thesis, 2020.
Abstract:
Social influence networks are collections of entities dealing with a shared issue on which they have individual opinions. These opinions are dynamic, changing over time due to influence from other entities. Mechanisms within the network can affect how influence leads to opinion change, such as the strength and number of social ties between agents and the decision models used by an individual to process information from its neighbors. In real-world scenarios, these mechanisms are often hidden. Much effort in social network analysis involves proposing models and attempting to replicate target output data with them. Can we instead use the evolution of opinions in a network to infer these mechanisms directly?
This work explores how opinion change in social influence networks can be used to determine characteristics of those networks. Broadly, this is accomplished by simulating social influence networks using various designs and initial conditions to generate opinion data, and then identifying relationships between response variables and changes to the simulation inputs. Key inputs include the population size, the influence model that controls how agents change their opinions, the network structure, the activation regime that controls the sequencing of opinion updates, and probability distributions for communication errors. Analyzing the opinions of individual agents can provide insights about the individuals (microscopic), but in this work, focus is on insights into the social influence network as a complete system (macroscopic), so opinion data is aggregated according to each response variable.
Response variables are designed through the lens of complexity theory. Three types of complexity measurements are applied to opinion data: regression, entropy, and a new complexity measure. In each case, relationships between design factors and response variables are diverse. The influence model and the distribution of communication errors---a factor often omitted from the literature---are consistently impactful, with their various settings producing distinct profiles in time series plots of the measurements. Activation regime is impactful to some entropy measures. Network structure has little impact on the new complexity measure, and population size has little impact in general. Overall, distinctive relationships can exist between opinions and design factors. These relationships, as well as the measures and problem-solving approaches used in this work, may be helpful to analysts working to infer the properties of real-world social influence networks from the opinion data those systems generate.
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Hsu, Hsiang-Yao, and 徐祥耀. "The Macroscopic and Microscopic Simulation of the Carbon-Coated Si Anode Lithium-ion Batteries." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/52046357928711846466.
Abstract:
碩士國立臺灣大學
化學工程學研究所
101
Lithium-ion batteries have the characteristics of high energy densities, high operate voltage, large output power, and high cycle life. In addition, the low self-discharge rates and the long storage life, making lithium-ion batteries well suited for 3C applications and stationary applications. The mathematical modeling of lithium-ion battery has been developed in this study, based on electrochemistry, combined with thermodynamics, transport phenomena, ohm’s law, and electrochemical kinetics, the model systems was simulated by computer-aided software engineering. The one-dimensional (flow) model was solved by COMSOL 4.3a software, and the Butler–Volmer equation was solved by MATLAB. The results were compared to the P2D model in COMSOL and the experiments which were performed on CR2032 Li-ion cell with various negative electrode materials (KS-6 graphite, Silicon, C-coated Si, and KS-6/Si). Two different approaches have employed to model the insertion of lithium ions into an negative electrode particle: the Fick''s second law and the nonlinear diffusion model considering the vacancy effect. Then, the model system was then scaled up to a cylindrical 18650 lithium cobalt oxide cell. By changing the manufacturing parameters, various effects on the batteries performance would be investigated. Using small particles, increasing the diffusion coefficient of lithium in solid state, and less electrode porosity could increase the discharge capacity. The model involving SEI formation has been developed to simulate the capacity fade of 18650 Li-ion batteries in first few cycles. The largest capacity losses due to solid electrolyte interphase (SEI) growth have been found in the first cycle, and were steady in the next several cycles.
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Richardson, Ashlin D. "Refined macroscopic traffic modelling via systems of conservation laws." Thesis, 2012. http://hdl.handle.net/1828/4304.
Abstract:
We elaborate upon the Herty-Illner macroscopic traffic models which include special non-local forces. The first chapter presents these in relation to the traffic models of Aw-Rascle and Zhang, arguing that non-local forces are necessary for a realistic description of traffic.
The second chapter considers travelling wave solutions for the Herty-Illner macroscopic models. The travelling wave ansatz for the braking scenario reveals a curiously implicit nonlinear functional differential equation, the jam equation, whose unknown is, at least to conventional tools, inextricably self-argumentative! Observing that analytic solution methods fail for the jam equation yet succeed for equations with similar coefficients raises a challenging problem of pure and applied mathematical interest. An unjam equation analogous to the jam equation explored by Illner and McGregor is derived.
The third chapter outlines refinements for the Herty-Illner models. Numerics allow exploration of the refined model dynamics in a variety of realistic traffic situations, leading to a discussion of the broadened applicability conferred by the refinements: ultimately the prediction of stop-and-go waves.
The conclusion asserts that all of the above contribute knowledge pertinent to traffic control for reduced congestion and ameliorated vehicular flow.Graduate
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TONAZZI, DAVIDE. "Macroscopic frictional contact scenarios and local contact dynamics: at the origins of “macroscopic stick-slip”, mode coupling instabilities and stable continuous sliding." Doctoral thesis, 2014. http://hdl.handle.net/11573/863973.
Abstract:
Local contact behavior and its interaction with the global dynamics of the system are at the origin of innumerable contact issues concerning several different disciplines like tribology, geophysics, vibration mechanics or fracture mechanics.
When two elastic media are in relative motion with a frictional interface, friction induced vibrations arise into the system. By a macroscopic point of view, the “macroscopic stick-slip” scenario occurring during relative motion is characterized by sudden friction force drops (sliding state) along the time, separated by periods of elastic energy accumulation (stick state). Instead, the mode dynamic instability occurs when a vibration mode of the mechanical system becomes unstable, due to frictional contact forces. This kind of instabilities, generated by frictional forces, have been mainly object of papers dealing with specific issues in different domains such as brake squeal, hip endoprosthesis squeaking, wheel-rail vibrations, earthquakes, etc.
In this context, experimental and numerical analyses have been focused here on understanding how the local interface behavior affects the macroscopic frictional response of the system, and, conversely, during instability scenarios.
The macroscopic frictional scenarios (macroscopic stick-slip instability, mode coupling instability, stable continuous sliding) arising between two simple elastic media in relative motion have been investigated numerically and experimentally. A newer experimental setup (TRIBOWAVE) has been developed and it allowed to reproduce and to investigate the different scenarios under well-controlled boundary conditions.
The same frictional scenarios have been reproduced by transient numerical simulations. A dedicated friction law as a function of adherence (sticking) time has been recovered by means of experimental tests. The obtained friction law has been implemented in the numerical model, leading to a quantitative validation of the simulated scenarios by the experiments.
Nonlinear transient simulations, complex eigenvalue analyses and experimental tests allowed for drawing instability maps as a function of system key parameters.
The numerical model, validated by the comparison with the experimental global measurements (forces, accelerations/velocity), allowed for investigating the coupling between the local contact behavior (contact status distribution, wave and rupture propagation, precursors) and the system dynamic response during macroscopic stick-slip instability, mode coupling instability and stable continuous sliding.
The understanding of the coupling between contact and system dynamics will bring to further improvements on the control of contact instabilities and related wear issues.
42
Sanyal, Dipayan. "Numerical Simulation of Some Aspects of Transport Phenomena at Macroscopic and Microscopic Levels during Solidification." Thesis, 2004. http://cgcri.csircentral.net/3260/.
43
Schurig, Michael [Verfasser]. "The Vertex effect in polycrystalline materials : simulation, a macroscopic model, and structural application / von Michael Schurig." 2006. http://d-nb.info/981983359/34.
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Beckmann, Alexander Felix. "Modeling evaporation in the rarefied gas regime by using macroscopic transport equations." Thesis, 2018. https://dspace.library.uvic.ca//handle/1828/9238.
Abstract:
Due to failure of the continuum hypothesis for higher Knudsen numbers, rarefied gases and microflows of gases are particularly difficult to model. Macroscopic transport equations compete with particle methods, such as the direct simulation Monte Carlo method (DSMC) to find accurate solutions in the rarefied gas regime. Due to growing interest in micro flow applications, such as micro fuel cells, it is important to model and understand evaporation in this flow regime. To gain a better understanding of evaporation physics, a non-steady simulation for slow evaporation in a microscopic system, based on the Navier-Stokes-Fourier equations, is conducted. The one-dimensional problem consists of a liquid and vapor layer (both pure water) with respective heights of 0.1mm and a corresponding Knudsen number of Kn=0.01, where vapor is pumped out. The simulation allows for calculation of the evaporation rate within both the transient process and in steady state. The main contribution of this work is the derivation of new evaporation boundary conditions for the R13 equations, which are macroscopic transport equations with proven applicability in the transition regime. The approach for deriving the boundary conditions is based on an entropy balance, which is integrated around the liquid-vapor interface. The new equations utilize Onsager relations, linear relations between thermodynamic fluxes and forces, with constant coefficients that need to be determined. For this, the
boundary conditions are fitted to DSMC data and compared to other R13 boundary conditions from kinetic theory and Navier-Stokes-Fourier solutions for two steady-state, one-dimensional problems. Overall, the suggested fittings of the new phenomenological boundary conditions show better agreement to DSMC than the alternative kinetic theory evaporation boundary conditions for R13. Furthermore, the new evaporation boundary conditions for R13 are implemented in a code for the numerical solution of complex, two-dimensional geometries and compared to Navier-Stokes-Fourier (NSF) solutions. Different flow patterns between R13 and NSF for higher Knudsen numbers are observed which suggest continuation of this work.Graduate
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Kimmerle, Sven-Joachim [Verfasser]. "Macroscopic diffusion models for precipitation in crystalline gallium arsenide : modelling, analysis and simulation / von Sven-Joachim Wolfgang Kimmerle." 2009. http://d-nb.info/1002315824/34.
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Carter, W. Craig. "Computation and Simulation of the Effect of Microstructures on Material Properties." 2002. http://hdl.handle.net/1721.1/3970.
Abstract:
Methods for and computed results of including the physics and spatial attributes of microstructures are presented for a number of materials applications in devices. The research in our group includes applications of computation of macroscopic response of material microstructures, the development of methods for calculating microstructural evolution, and the morphological stability of structures. In this review, research highlights are presented for particular methods for computing the response in: 1) ferroelectric materials for actuator devices; 2) coarse-graining of atomistic data for simulations of microstructural evolution during processing; 3) periodic and non-periodic photonic composites; and 4) re-chargeable battery microstructures.Singapore-MIT Alliance (SMA)
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AMABILI, MATTEO. "Stability of the submerged superhydrophobic state via rare event molecular dynamics simulations." Doctoral thesis, 2017. http://hdl.handle.net/11573/936817.
Abstract:
In the present thesis the stability of the superhydrophobic state on submerged nanotextured surfaces with complex chemistry and geometry is investigated via rare event molecular dynamics simulations. Superhydrophobicity stems from the presence of vapor or gas pockets trapped within the surface texture sustaining the liquid atop of the textures. This superhydrophobic --or Cassie-- state gives rise to remarkable macroscopic properties, such as enhancing liquid slip at the surface or resulting into anti-fouling capabilities. These and many other properties make superhydrophobic surfaces promising for a wide range of technological applications. Superhydrophobicity can be lost via two mechanisms: i) liquid intrusion, i.e. the filling of the liquid inside the textures, leading to the fully wet Wenzel state, or ii) vapor cavitation, i.e. the formation, growth, detachment of a (supercritical) vapor or gas bubble, and the ensuing replacement of the vapor pocket by the liquid. Understanding the mechanism of the Cassie-Wenzel and cavitation transitions is crucial in order to define quantitatively the stability of the superhydrophobic state. These transitions are typically characterized by large free-energy barriers. The presence of these barriers make the study of the transitions particularly challenging due to the diverse timescales present in the problem. Indeed, these transitions are rare events, i.e., they happen on timescale which cannot be simulated by standard molecular dynamics methods. Thus, in order to tackle this issue, rare event methods are used which allow one to compute the free-energy barriers and the mechanism of the transition. This information is essential for developing new design criteria which can pave the way to a new generation of surfaces with more stable superhydrophobic properties in submerged conditions. In the first part of the thesis, re-entrant surface textures are investigated. The focus on this geometry is due to the increasing interest on textures which show omniphobic properties, i.e., which allows the formation of the Cassie state also for low surface tension liquids. Our atomistic results are compared with a macroscopic sharp-interface continuum model. While the two models are generally in fair agreement, quantitative differences were found in the cavitation free-energy barriers, with the macroscopic model overestimating them. The major qualitative difference concerns the behaviour of the system in the Wenzel state, where only the atomistic model can capture the presence of the confined liquid spinodal. These results also allowed us to develop design criteria for textured submerged superhydrophobic surface. The role of the chemistry of the surface was also studied. Pure hydrophobic, pure hydrophilic, and mixed, i.e. internally hydrophobic and externally hydrophilic surfaces, were considered. It was found that the free energy of the mixed chemistry surface closely resemble the superimposition of the one of pure hydrophilic and hydrophobic chemistries. The mixed chemistry shows improved stability of gas pockets against both liquid intrusion and vapor cavitation. Finally, the combined effect of complex chemistry and geometry, such as re-entrant pore morphologies, was also investigated. This latter part of the work was primarily inspired by the natural case of Salvinia molesta, which is a floating fern capable of remaining dry even after a long underwater immersion. Salvinia leaves show similar features with respect to the proposed textures; it is characterized by hairs with a peculiar re-entrant structure with a heterogeneous chemistry: a hydrophobic interior and an hydrophilic patch on the hairs top. In the second part of the thesis, the Cassie-Wenzel transition was investigated on a submerged 3D nano pillared surface. Here, a state-of-the-art technique, the string method, was employed in order to compute the most probable transition mechanism and the corresponding free-energy barrier. The coarse-grained fluid density field was used as a collective variable to characterize the transition. Results are both of applicative and of methodological interst. For the former, the string method revealed the actual transition mechanism, which proceeds by breaking the 2D translational symmetry of the surface textures. These results are interpreted in terms of a sharp-interface continuum model suggesting that nanoscale effects, e.g., line tension, play a minor role in the considered conditions. Concerning to the former, the effect of the choice of the collective variables, i.e. different level of coarse-graining of the fluid density field, was studied. Results show the correct level of coarse-graining suited to correctly capture the transition mechanism and the free-energy barrier.
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Jendrejack, Richard M. "Multiscale simulations of dilute-solution macromolecular dynamics in macroscopic and microscopic geometries." 2003. http://www.library.wisc.edu/databases/connect/dissertations.html.
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Lätzel, Marc [Verfasser]. "From microscopic simulations towards a macroscopic description of granular media / vorgelegt von Marc Lätzel." 2003. http://d-nb.info/96721002X/34.
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Golubnychiy, Volodymyr [Verfasser]. "Molecular dynamics simulations of strongly correlated mesoscopic and macroscopic Coulomb systems / vorgelegt von Volodymyr Golubnychiy." 2004. http://d-nb.info/972353062/34.