Дисертації з теми "High-order modeling"
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Charous, Aaron( Aaron Solomon). "High-order retractions for reduced-order modeling and uncertainty quantification." Thesis, Massachusetts Institute of Technology, 2006. https://hdl.handle.net/1721.1/130904.
Повний текст джерелаCataloged from the official PDF version of thesis.
Includes bibliographical references (pages 145-151).
Though computing power continues to grow quickly, our appetite to solve larger and larger problems grows just as fast. As a consequence, reduced-order modeling has become an essential technique in the computational scientist's toolbox. By reducing the dimensionality of a system, we are able to obtain approximate solutions to otherwise intractable problems. And because the methodology we develop is sufficiently general, we may agnostically apply it to a plethora of problems, whether the high dimensionality arises due to the sheer size of the computational domain, the fine resolution we require, or stochasticity of the dynamics. In this thesis, we develop time integration schemes, called retractions, to efficiently evolve the dynamics of a system's low-rank approximation. Through the study of differential geometry, we are able to analyze the error incurred at each time step. A novel, explicit, computationally inexpensive set of algorithms, which we call perturbative retractions, are proposed that converge to an ideal retraction that projects exactly to the manifold of fixed-rank matrices. Furthermore, each perturbative retraction itself exhibits high-order convergence to the best low-rank approximation of the full-rank solution. We show that these high-order retractions significantly reduce the numerical error incurred over time when compared to a naive Euler forward retraction. Through test cases, we demonstrate their efficacy in the cases of matrix addition, real-time data compression, and deterministic and stochastic differential equations.
by Aaron Charous.
S.M.
S.M. Massachusetts Institute of Technology, Center for Computational Science & Engineering
Charous, Aaron (Aaron Solomon). "High-order retractions for reduced-order modeling and uncertainty quantification." Thesis, Massachusetts Institute of Technology, 2021. https://hdl.handle.net/1721.1/130904.
Повний текст джерелаCataloged from the official PDF version of thesis.
Includes bibliographical references (pages 145-151).
Though computing power continues to grow quickly, our appetite to solve larger and larger problems grows just as fast. As a consequence, reduced-order modeling has become an essential technique in the computational scientist's toolbox. By reducing the dimensionality of a system, we are able to obtain approximate solutions to otherwise intractable problems. And because the methodology we develop is sufficiently general, we may agnostically apply it to a plethora of problems, whether the high dimensionality arises due to the sheer size of the computational domain, the fine resolution we require, or stochasticity of the dynamics. In this thesis, we develop time integration schemes, called retractions, to efficiently evolve the dynamics of a system's low-rank approximation. Through the study of differential geometry, we are able to analyze the error incurred at each time step. A novel, explicit, computationally inexpensive set of algorithms, which we call perturbative retractions, are proposed that converge to an ideal retraction that projects exactly to the manifold of fixed-rank matrices. Furthermore, each perturbative retraction itself exhibits high-order convergence to the best low-rank approximation of the full-rank solution. We show that these high-order retractions significantly reduce the numerical error incurred over time when compared to a naive Euler forward retraction. Through test cases, we demonstrate their efficacy in the cases of matrix addition, real-time data compression, and deterministic and stochastic differential equations.
by Aaron Charous.
S.M.
S.M. Massachusetts Institute of Technology, Center for Computational Science & Engineering
Velechovsky, Jan. "High-order numerical methods for laser plasma modeling." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0098/document.
Повний текст джерелаThis thesis presents the overview and the original contributions to a high–orderArbitrary Lagrangian–Eulerian (ALE) method applicable for the laser–generated plasma modeling withthe focus to a remapping step of the ALE method. The remap is the conservative interpolation of theconservative quantities from a low–quality Lagrangian grid onto a better, smoothed one. To avoidnon–physical numerical oscillations, the high–order numerical fluxes of the reconstruction arecombined with the low–order (first–order) numerical fluxes produced by a standard donor remappingmethod. The proposed method for a cell–centered discretization preserves bounds for the density,velocity and specific internal energy by its construction. Particular symmetry–preserving aspects of themethod are applied for a staggered momentum remap. The application part of the thesis is devoted tothe laser radiation absorption modeling in plasmas and microstructures materials with the particularinterest in the laser absorption in low–density foams. The absorption is modeled on two spatial scalessimultaneously. This two–scale laser absorption model is implemented in the hydrodynamic codePALE. The numerical simulations of the velocity of laser penetration in a low–density foam are in agood agreement with the experimental data
Heidkamp, Holger [Verfasser]. "Modeling Localization and Failure with High-Order Finite Elements / Holger Heidkamp." Aachen : Shaker, 2008. http://d-nb.info/1164341642/34.
Повний текст джерелаBeisiegel, Nicole [Verfasser], and Jörn [Akademischer Betreuer] Behrens. "High-order Adaptive Discontinuous Galerkin Inundation Modeling / Nicole Beisiegel. Betreuer: Jörn Behrens." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/1060484749/34.
Повний текст джерелаBeisiegel, Nicole Verfasser], and Jörn [Akademischer Betreuer] [Behrens. "High-order Adaptive Discontinuous Galerkin Inundation Modeling / Nicole Beisiegel. Betreuer: Jörn Behrens." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://nbn-resolving.de/urn:nbn:de:gbv:18-70360.
Повний текст джерелаTong, Oisin. "Development of a Three-Dimensional High-Order Strand-Grids Approach." DigitalCommons@USU, 2016. https://digitalcommons.usu.edu/etd/4711.
Повний текст джерелаYe, Fei. "Developing Efficient High-Order Transport Schemes for Cross-Scale Coupled Estuary-Ocean Modeling." W&M ScholarWorks, 2017. https://scholarworks.wm.edu/etd/1516639591.
Повний текст джерелаCollins, Justin A. Valentine Jerry. "Higher-order thinking in the high-stakes accountability era linking student engagement and test performance /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2009. http://hdl.handle.net/10355/6769.
Повний текст джерелаPowers, Sean W. "Analysis of Stresses in Metal Sheathed Thermocouples in High-Temperature, Hypersonic Flows." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/98000.
Повний текст джерелаM.S.
Thermocouples are a device for measuring temperature, consisting of two wires of different metals connected at two different points. This configuration produces a temperature-dependent voltage as a result of the thermoelectric effect. Preexisting curves are used to relate the voltage to temperature. Thermocouples are extensively used in high-temperature high-stress environments such as in rockets, jet engines, or any high-corrosive environment. Accurately predicting the stresses within the sheath of a metal-clad thermocouple in extreme conditions is required for many research areas including hypersonic aerodynamics and various propulsion applications. Even for these extremely well-developed and widely used sensors, the accurate prediction of stresses within the metal sheath remains a topic of great concern for ensuring the sensor’s survivability in these extreme conditions. Current engineering practice is to use high-fidelity numerical simulations (Finite Element Analysis) to predict the stresses within the sheath. Perhaps the biggest drawback to this approach is the time it takes to model, mesh, and set-up these simulations. Comparative studies between different designs using numerical simulations are almost impossible due to the time requirement. This Thesis will present an analytically derived quasi-3D solution to find the stresses within the sheath. These equations were implemented into a low-order model that can handle varying temperature, geometry, and material inputs. This model was validated against both high-fidelity numerical simulations (ANSYS Mechanical) and a simplified experiment. The predictions using this newly developed structural low-order model are in excellent agreement with the numerically simulated results and experimental results.
Cohan, Daniel Shepherd. "Photochemical Formation and Cost-Efficient Abatement of Ozone: High-Order Sensitivity Analysis." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-09152004-150617/unrestricted/cohan%5Fdaniel%5Fs%5F200412%5Fphd.pdf.
Повний текст джерелаRussell, Armistead G., Committee Chair ; Chameides, William L., Committee Member ; Wang, Yuhang, Committee Member ; Noonan, Douglas, Committee Member ; Chang, Michael E., Committee Member. Vita. Includes bibliographical references.
Rambo, Jeffrey D. "Reduced-Order Modeling of Multiscale Turbulent Convection: Application to Data Center Thermal Management." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-03272006-080024/.
Повний текст джерелаMarc Smith, Committee Member ; P.K. Yeung, Committee Member ; Benjamin Shapiro, Committee Member ; Sheldon Jeter, Committee Member ; Yogendra Joshi, Committee Chair.
Gopalan, Harish. "Numerical Modeling of Aerodynamics of Airfoils of Micro Air Vehicles in Gusty Environment." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1221497568.
Повний текст джерелаPasha, Soheila. "Electromagnetic Modeling of High-Speed Interconnects with Frequency Dependent Conductor Losses, Compatible with Passive Model Order Reduction Techniques." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/268354.
Повний текст джерелаTorberntsson, Kim, and Vidar Stiernström. "A High Order Finite Difference Method for Simulating Earthquake Sequences in a Poroelastic Medium." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-298414.
Повний текст джерелаRodríguez, Fernández Jhan Ignacio [Verfasser], and András [Akademischer Betreuer] Bárdossy. "High order interactions among environmental variables : diagnostics and initial steps towards modeling / Jhan Ignacio Rodríguez Fernández. Betreuer: András Bárdossy." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1046564404/34.
Повний текст джерелаLaurent, Charlelie. "Low-order modeling and high-fidelity simulations for the prediction of combustion instabilities in liquid rocket engines and gas turbines." Thesis, Toulouse, INPT, 2020. http://www.theses.fr/2020INPT0038.
Повний текст джерелаOver the last decades, combustion instabilities have been a major concern for a number of industrial projects, especially in the design of Liquid Rocket Engines (LREs) and gas turbines. Mitigating their effects requires a solid scientific understanding of the intricate interplay between flame dynamics and acoustic waves that they involve. During this PhD work, several directions were explored to provide a better comprehension of flame dynamics in cryogenic rocket engines, as well as more efficient and robust numerical methods for the prediction of thermoacoustic instabilities in complex combustors. The first facet of this work consisted in the resolution of unstable thermoacoustic modes in complex multi-injectors combustors, a task that often requires a number of simplifications to be computationally affordable. These necessary physics-based assumptions led to the growing popularity of acoustic Low-Order Models (LOMs), among which Galerkin expansion LOMs have displayed a promising efficiency while retaining a satisfactory accuracy. Those are however limited to simple geometries that do not incorporate the complex features of industrial systems. A major part of this work therefore consisted first in clearly identifying the mathematical limitations of the classical Galerkin expansion, and then in designing a novel type of modal expansion, named a frame expansion, that does not suffer from the same restrictions. In particular, the frame expansion is able to accurately represent the acoustic velocity field, near non-rigid-wall boundaries of the combustor, a crucial ability that the Galerkin method lacks. In this work, the concept of surface modal expansion is also introduced to model topologically complex boundaries, such as multi-perforated liners encountered in gas turbines. These novel numerical methods were combined with the state-space formalism to build acoustic networks of complex systems. The resulting LOM framework was implemented in the code STORM (State-space Thermoacoustic low-ORder Model), which enables the low-order modeling of thermoacoustic instabilities in arbitrarily complex geometries. The second ingredient in the prediction of thermoacoustic instabilities is the flame dynamics modeling. This work dealt with this problem, in the specific case of a cryogenic coaxial jet-flame characteristic of a LRE. Flame dynamics driving phenomena were identified thanks to three-dimensional Large Eddy Simulations (LES) of the Mascotte experimental test rig where both reactants (CH4 and O2) are injected in transcritical conditions. A first simulation provides a detailed insight into the flame intrinsic dynamics. Several LES with harmonic modulation of the fuel inflow at various frequencies and amplitudes were performed in order to evaluate the flame response to acoustic oscillations and compute a Flame Transfer Function (FTF). The flame nonlinear response, including interactions between intrinsic and forced oscillations, were also investigated. Finally, the stabilization of this flame in the near-injector region, which is of primary importance on the overall flame dynamics, was investigated thanks to muulti-physics two-dimensional Direct Numerical Simulations (DNS), where a conjugate heat transfer problem is resolved at the injector lip
Crowell, Andrew R. "Model Reduction of Computational Aerothermodynamics for Multi-Discipline Analysis in High Speed Flows." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366204830.
Повний текст джерелаDreyer, Emily Rose. "Assessment of Reduced Fidelity Modeling of a Maneuvering Hypersonic Vehicle." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1610018486409227.
Повний текст джерелаZhang, Wenxian. "Direct sensitivity techniques in regional air quality models: development and application." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52941.
Повний текст джерелаRuan, Kangping. "NUMERICAL AND EXPERIMENTAL TECHNIQUES FOR ASSESSING THE ACOUSTIC PERFORMANCE OF DUCT SYSTEMS ABOVE THE PLANE WAVE CUTOFF FREQUENCY." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/120.
Повний текст джерелаMoglan, Raluca. "Modeling and numerical simulation of flow and heat phenomena in a telecommunication heat cabinet." Rouen, 2013. http://www.theses.fr/2013ROUES060.
Повний текст джерелаIn this thesis we present a new 3D approach for solving the incompressible Navier-Stokes equations under the Boussinesq approximation. The advantage of the developed numerical code is the use of high order methods for time integration (3rd order Runge-Kutta method) and spatial discretization (6th order finite difference schemes). A study of the order of the numerical method was made, followed by an extensive validation for several cases of natural convection. A finite element simulation code for the same problem was developed using FreeFem++, and was validated with respect to the same cases of natural convection. The case of a telecommunication cabinet was treated by modelling interior obstacles generating heat using an immersed boundary method. This method was validated with respect to the finite element simulation, and many other cases from the literature. We present the results for different 2D and 3D configurations, with obstacles differently placed inside the cavity. Results are also presented for the comparison with experimental measurements in a cabinet with two components dissipating heat. The finite element code is finally extended and tested to simulate phase change materials that could serve as passive cooling devices
Ferrer, Esteban. "A high order Discontinuous Galerkin - Fourier incompressible 3D Navier-Stokes solver with rotating sliding meshes for simulating cross-flow turbines." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:db8fe6e3-25d0-4f6a-be1b-6cde7832296d.
Повний текст джерелаLegrand, Nicolas. "Numerical and modeling methods for multi-level large eddy simulations of turbulent flows in complex geometries." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMIR16/document.
Повний текст джерелаLarge-Eddy Simulation (LES) has become a major tool for the analysis of highly turbulent flows in complex geometries. However, due to the steadily increase of computational resources, the amount of data generated by well-resolved numerical simulations is such that it has become very challenging to manage them with traditional data processing tools. In Computational Fluid Dynamics (CFD), this emerging problematic leads to the same "Big Data" challenges as in the computer science field. Some techniques have already been developed such as data partitioning and ordering or parallel processing but still remain insufficient for modern numerical simulations. Hence, the objective of this work is to propose new processing formalisms to circumvent the data volume issue for the future 2020 exa-scale computing objectives. To this aim, a massively parallel co-processing method, suited for complex geometries, was developed in order to extract large-scale features in turbulent flows. The principle of the method is to introduce a series of coarser nested grids to reduce the amount of data while keeping the large scales of interest. Data is transferred from one grid level to another using high-order filters and accurate interpolation techniques. This method enabled to apply modal decomposition techniques to a billion-cell LES of a 3D turbulent turbine blade, thus demonstrating its effectiveness. The capability of performing calculations on several embedded grid levels was then used to devise the multi-resolution LES (MR-LES). The aim of the method is to evaluate the modeling and numerical errors during an LES by conducting the same simulation on two different mesh resolutions, simultaneously. This error estimation is highly valuable as it allows to generate optimal grids through the building of an objective grid quality measure. MR-LES intents to limit the computational cost of the simulation while minimizing the sub-grid scale modeling errors. This novel framework was applied successfully to the simulation of a turbulent flow around a 3D cylinder
Ueckermann, Mattheus Percy. "High order hybrid discontinuous Galerkin regional ocean modelling." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87984.
Повний текст джерелаCataloged from PDF version of thesis.
Includes bibliographical references (pages 343-357).
Accurate modeling of physical and biogeochemical dynamics in coastal ocean regions is required for multiple scientific and societal applications, covering a wide range of time and space scales. However, in light of the strong nonlinearities observed in coastal regions and in biological processes, such modeling is challenging. An important subject that has been largely overlooked is the numerical requirements for regional ocean simulation studies. Major objectives of this thesis are to address such computational questions for non-hydrostatic multiscale flows and for biogeochemical interactions, and to derive and develop numerical schemes that meet these requirements, utilizing the latest advances in computational fluid dynamics. We are interested in studying nonlinear, transient, and multiscale ocean dynamics over complex geometries with steep bathymetry and intricate coastlines, from sub-mesoscales to basin-scales. These dynamical interests, when combined with our requirements for accurate, efficient and flexible ocean modeling, led us to develop new variable resolution, higher-order and non-hydrostatic ocean modeling schemes. Specifically, we derived, developed and applied new numerical schemes based on the novel hybrid discontinuous Galerkin (HDG) method in combination with projection methods. The new numerical schemes are first derived for the Navier-Stokes equations. To ensure mass conservation, we define numerical fluxes that are consistent with the discrete divergence equation. To improve stability and accuracy, we derive a consistent HDG stability parameter for the pressure-correction equation. We also apply a new boundary condition for the pressure-corrector, and show the form and origin of the projection method's time-splitting error for a case with implicit diffusion and explicit advection. Our scheme is implemented for arbitrary, mixed-element unstructured grids using a novel quadrature-free integration method for a nodal basis, which is consistent with the HDG method. To prevent numerical oscillations, we design a selective high-order nodal limiter. We demonstrate the correctness of our new schemes using a tracer advection benchmark, a manufactured solution for the steady diffusion and stokes equations, and the 2D lock-exchange problem. These numerical schemes are then extended for non-hydrostatic, free-surface, variable-density regional ocean dynamics. The time-splitting procedure using projection methods is derived for non-hydrostatic or hydrostatic, and nonlinear free-surface or rigid-lid, versions of the model. We also derive consistent HDG stability parameters for the free-surface and non-hydrostatic pressure-corrector equations to ensure stability and accuracy. New boundary conditions for the free-surface-corrector and pressure-corrector are also introduced. We prove that these conditions lead to consistent boundary conditions for the free-surface and pressure proper. To ensure discrete mass conservation with a moving free-surface, we use an arbitrary Lagrangian- Eulerian (ALE) moving mesh algorithm. These schemes are again verified, this time using a tidal flow problem with analytical solutions and a 3D lock-exchange benchmark. We apply our new numerical schemes to evaluate the numerical requirements of the coupled biological-physical dynamics. We find that higher-order schemes are more accurate at the same efficiency compared to lower-order (e.g. second-order) accurate schemes when modeling a biological patch. Due to decreased numerical dissipation, the higher-order schemes are capable of modeling biological patchiness over a sustained duration, while the lower-order schemes can lose significant biomass after a few non-dimensional times and can thus solve erroneous nonlinear dynamics. Finally, inspired by Stellwagen Bank in Massachusetts Bay, we study the effect of non-hydrostatic physics on biological productivity and phytoplankton fields for tidally-driven flows over an idealized bank. We find that the non-hydrostatic pressure and flows are important for biological dynamics, especially when flows are supercritical. That is, when the slope of the topography is larger than the slope of internal wave rays at the tidal frequency. The non-hydrostatic effects increase with increasing nonlinearity, both when the internal Froude number and criticality parameter increase. Even in cases where the instantaneous biological productivity is not largely modified, we find that the total biomass, spatial variability and patchiness of phytoplankton can be significantly altered by non-hydrostatic processes. Our ultimate dynamics motivation is to allow quantitative simulation studies of fundamental nonlinear biological-physical dynamics in coastal regions with complex bathymetric features such as straits, sills, ridges and shelfbreaks. This thesis develops the necessary numerical schemes that meet the stringent accuracy requirements for these types of flows and dynamics.
by Mattheus Percy Ueckermann.
Ph. D.
Schmidt, Kersten. "High-order numerical modelling of highly conductive thin sheets /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17903.
Повний текст джерелаMifsud, Michael. "Reduced-order modelling for high-speed aerial weapon aerodynamics." Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3511.
Повний текст джерелаZachariadis, Zacharias Ioannis. "High resolution and high order methods for RANS modelling and aerodynamic optimization." Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3806.
Повний текст джерелаBrandi, Analice Costacurta. "Estratégias "upwind" e modelagem k-epsilon para simulação numérica de escoamentos com superfícies livres em altos números de Reynolds." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-01122005-170110/.
Повний текст джерелаThis work is devoted to the analysis and implementation of modern high-order upwind schemes and the standard k-epsilon turbulence model into the Freeflow-2D; a finite difference integrated environment for the numerical simulation of incompressible free surface flow problems. The purpose of this study is the two-dimensional simulation of high-Reynolds incompressible newtonian confined and/or free surface flows. The performance of the current Freeflow-2D code is assessed by applying it to the simulation of flow over a backward facing step and of an impinging free jet onto an impermeable rigid surface. The code is then applied to a turbulent planar jet into a pool. The numerical results are compared with experimental data, analytical solution, and numerical simulations of other works.
Mosedale, Andrew Daniel. "Modelling shock-induced instabilities, transition and turbulent mixing using high-order methods." Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3791.
Повний текст джерелаBotti, Michele. "Advanced polyhedral discretization methods for poromechanical modelling." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS041/document.
Повний текст джерелаIn this manuscript we focus on novel discretization schemes for solving the coupled equations of poroelasticity and we present analytical and numerical results for poromechanics problems relevant to geoscience applications. We propose to solve these problems using Hybrid High-Order (HHO) methods, a new class of nonconforming high-order methods supporting general polyhedral meshes. This Ph.D. thesis was conjointly founded by the Bureau de recherches géologiques et minières (BRGM) and LabEx NUMEV. The coupling between subsurface flow and geomechanical deformation is a crucial research topic for both cofunding institutions
From, Christopher. "High-order lattice Boltzmann for nonideal fluid mixtures." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/200190/1/Christopher_From_Thesis.pdf.
Повний текст джерелаMall, Suneeta. "Modelling the interpretation of digital mammography using high order statistics and deep machine learning." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19987.
Повний текст джерелаCanestrelli, Alberto. "Numerical Modelling of Alluvial Rivers by Shock Capturing Methods." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3421764.
Повний текст джерелаLa modellazione dell’idrodinamica e delle variazioni orfologiche in canali naturali `e generalmente effettuata risolvendo numericamente le equazioni delle onde lunghe in acque basse, che regolano il moto della fase fluida, assieme all’equazione di Exner, che descrive l’evoluzione del fondo. L’argomento della presente tesi consiste nello sviluppo di un schema ai volumi finiti di tipo ”centrato” per la soluzione accoppiata di tale sistema di equazioni. Un nuovo schema, denominato PRICE-C, `e qui introdotto: esso risolve le equazioni in forma conconservativa, ma ha l’importante propriet`a di degenerare in uno schema conservativo se il sottostante sistema di equazioni ammette una forma conservativa. Lo schema `e applicato alle equazioni delle onde lunghe in acque basse sia nel caso di fondo fisso che di fondo mobile, dapprima in un ambito unidimensionale e successivamente in quello bidimensionale. L’estensione non `e immediata nel caso in cui il reticolo di calcolo sia non-strutturato, dal momento che le equazioni differenziali devono essere mediate su opportuni volumi di controllo. Lo schema `e poi esteso ad alti ordini di accuratezza nello spazio e nel tempo attraverso le procedure ADER-WENO e MUSCL rispettivamente per il caso unidimensionale e bidimensionale. Inoltre si dimostra come lo schema proposto verifichi la ”well-balanced property”, che consiste nella capacit`a di raggiungere soluzioni stazionarie, anche in presenza di discontinuit`a della superficie libera e del fondo. Condizioni di corrente lenta e rapida, come pure condizioni di tipo transcritico vengono correttamente risolte. Inoltre lo schema in grado di riprodurre le celerit`a di propagazione di discontinuit`a della superficie e fronti di sedimenti al fondo, cos`? come la celerit`a di propagazione di piccoli disturbi del fondo. Caratteristica principale dello schema `e la sua semplicit`a: `e basato su un semplice approccio di tipo centrato, cio`e non necessita la conoscenza degli autovalori della matrice del sistema. Questa `e un’importante caratteristica dal momento che non sempre autovalori e autovettori sono calcolabili analiticamente, in particolare nel caso di complesse formule di chiusura per il trasporto al fondo. Quindi questo schema pu`o rivelarsi utile per l’ingegnere che spesso necessita di un semplice strumento numerico che possa essere applicato ad un sistema di equazioni differenziali di tipo iperbolico senza dover entrare nel dettaglio delle propriet`a atematiche del sistema stesso. Data la sua generalit`a, infatti, lo schema pu`o essere applicato ad ogni tipo di sistema iperbolico contenente termini non-conservativi.
Burton, Ludovic Nicolas. "Multi-Scale Thermal Modeling Methodology for High Power-Electronic Cabinets." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19808.
Повний текст джерелаLe, Touzé David. "Méthodes spectrales pour la modélisation non-linéaire d'écoulements à surface libre instationnaires." Phd thesis, Ecole centrale de nantes - ECN, 2003. http://tel.archives-ouvertes.fr/tel-00370200.
Повний текст джерелаUn bilan des différentes approches spectrales employées jusqu'à présent en hydrodynamique navale est d'abord dressé, étayant le choix des techniques développées au cours de ce travail. L'étude des propriétés de ces techniques est ensuite réalisée sur le ‘noyau' de la méthode, i.e. une cuve tri-dimensionnelle de géométrie figée. En particulier, différentes techniques High-Order Spectral sont comparées entre elles et à la méthode directe, et une nouvelle variante est proposée. Des validations sur des cas de lâchers de surface libre et d'oscillations forcées de surface libre sont présentées et confrontées à diverses méthodes.
L'approche est ensuite étendue, à partir de ce ‘noyau' et au moyen de stratégies de ‘potentiel additionnel', donnant lieu au développement de divers modèles. Ainsi, des houles non-linéaires sont modélisées à l'aide de doublets tournants instationnaires spécifiquement développés. Des cas de reproduction de signaux temporels cibles à une distance, et de génération et propagation de houle irrégulière sont présentés. De plus, une caractéristique avantageuse d'une telle approche spectrale est exploitée pour proposer des modèles originaux de diffraction autour de corps. Ceux-ci allient une génération de houle par méthode spectrale à des modèles de diffraction en fluide parfait ou visqueux, formulés en changement de variable. Des exemples illustratifs de diffraction de cette houle autour de corps bi- ou tri-dimensionnels sont proposés.
Enfin, un modèle original de simulation complète, au second-ordre, du processus de génération et propagation en bassin de houle tri-dimensionnel est réalisé. Il inclut la modélisation de différents batteurs, ainsi qu'un modèle d'absorption, permettant notamment de reproduire les caractéristiques complètes du nouveau bassin de houle de l'École Centrale de Nantes. Ce modèle est validé par comparaison à une solution analytique en régime établi et ses propriétés numériques sont étudiées. L'investigation des ondes libres et leur suppression, ainsi que la caractérisation de zones utiles sont proposées à titre d'application.
Thomas, Gregory Robert. "A combined high-order spectral and boundary integral equation method for modelling wave interactions with submerged bodies." Thesis, Monterey, California. Naval Postgraduate School, 1996. http://hdl.handle.net/10945/8098.
Повний текст джерелаThomas, Gregory Robert. "A combined high-order spectral and boundary integral equation method for modelling wave interactions with submerged bodies." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/17432.
Повний текст джерелаD'Alessio, Giuseppe. "Data-driven models for reacting flows simulations: reduced-order modelling, chemistry acceleration and analysis of high-fidelity data." Doctoral thesis, Universite Libre de Bruxelles, 2021. https://dipot.ulb.ac.be/dspace/bitstream/2013/328064/5/contratGA.pdf.
Повний текст джерелаDoctorat en Sciences de l'ingénieur et technologie
This thesis is submitted to the Université Libre de Bruxelles (ULB) and to the Politecnico di Milano for the degree of philosophy doctor. This doctoral work has been performed at the Université Libre de Bruxelles, École polytechnique de Bruxelles, Aero-Thermo-Mechanics Laboratory, Bruxelles, Belgium with Professor Alessandro Parente and at the Politecnico di Milano, CRECK Modelling Lab, Department of Chemistry, Materials and Chemical Engineering, Milan, Italy with Professor Alberto Cuoci.
info:eu-repo/semantics/nonPublished
Sim, Min Kyu. "Empirical findings in asset price dynamics revealed by quantitative modelling." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54302.
Повний текст джерелаShafieipour, Mohammad. "Efficient Error-Controllable High-Order Electromagnetic Modelling of Scattering on Electrically Large Targets with the Locally Corrected Nyström Method." IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, 2014. http://hdl.handle.net/1993/31181.
Повний текст джерелаMay 2016
Quint, Karsten [Verfasser]. "Thermomechanically coupled processes for functionally graded materials : experiments, modelling, and finite element analysis using high-order DIRK-methods / Karsten Quint." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2012. http://d-nb.info/1024717844/34.
Повний текст джерелаDucrozet, Guillaume. "Modélisation des processus non-linéaires de génération et de propagation d'états de mer par une approche spectrale." Phd thesis, Université de Nantes, 2007. http://tel.archives-ouvertes.fr/tel-00263596.
Повний текст джерелаUn traitement original de la génération de houle non-linéaire est proposé. Il permet l'accès à des simulations de champs de vagues tridimensionnels complexes, fortement cambrés, dans un bassin de houle. Diverses comparaisons avec des expériences menées dans le bassin du Laboratoire de Mécanique des Fluides de l'ECN sont présentées.
Des simulations océaniques, en milieu ouvert, sont également proposées. Un intérêt particulier est porté à l'étude de l'apparition des vagues scélérates au sein de l'océan. L'importance des effets non-linéaires est pointée ainsi que l'aptitude de la méthode à modéliser de tels phénomènes. Des comparaisons avec les méthodes classiquement employées dans ce genre de problématique indiquent l'intérêt de l'approche utilisée ici.
La résolution du problème de tenue à la mer est également envisagée. L'utilisation de la méthode HOS dans les codes couplés, développés au Laboratoire de Mécanique des Fluides (potentiel, RANS, SPH), est envisagée. Elle permettra la description précise de la houle incidente ; le couplage est mis en place et validé sur un certain nombre de cas d'application.
Steiert, Christoph, Juliane Weber, Alexander Galant, Janine Glänzel, and Jürgen Weber. "Fluid-thermal co-simulation for a high performance concrete machine frame." Technische Universität Dresden, 2020. https://tud.qucosa.de/id/qucosa%3A71161.
Повний текст джерелаSaliba, Pamela. "High-frequency trading : statistical analysis, modelling and regulation." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX044.
Повний текст джерелаThis thesis is made of two related parts. In the first one, we study the empirical behaviour of high-frequency traders on European financial markets. We use the obtained results to build in the second part new agent-based models for market dynamics. The main purpose of these models is to provide innovative tools for regulators and exchanges allowing them to design suitable rules at the microstructure level and to assess the impact of the various participants on market quality.In the first part, we conduct two empirical studies on unique data sets provided by the French regulator. It covers the trades and orders of the CAC 40 securities, with microseconds accuracy and labelled by the market participants identities. We begin by investigating the behaviour of high-frequency traders compared to the rest of the market, notably during periods of stress, in terms of liquidity provision and trading activity. We work both at the day-to-day scale and at the intra-day level. We then deepen our analysis by focusing on liquidity consuming orders. We give some evidence concerning their impact on the price formation process and their information content according to the different order flow categories: high-frequency traders, agency participants and proprietary participants.In the second part, we propose three different agent-based models. Using a Glosten-Milgrom type approach, the first model enables us to deduce the whole limit order book (bid-ask spread and volume available at each price) from the interactions between three kinds of agents: an informed trader, a noise trader and several market makers. It also allows us to build a spread forecasting methodology in case of a tick size change and to quantify the queue priority value. To work at the individual agent level, we propose a second approach where market participants specific dynamics are modelled by non-linear and state dependent Hawkes type processes. In this setting, we are able to compute several relevant microstructural indicators in terms of the individual flows. It is notably possible to rank market makers according to their own contribution to volatility. Finally, we introduce a model where market makers optimise their best bid and ask according to the profit they can generate from them and the inventory risk they face. We then establish theoretically and empirically a new important relationship between inventory and volatility
Larat, Adam. "Conception et Analyse de Schémas Distribuant le Résidu d'Ordre Très Élevé. Application à la Mécanique des Fluides." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2009. http://tel.archives-ouvertes.fr/tel-00502429.
Повний текст джерелаZebiri, Boubakr. "Étude numérique des interactions onde de choc / couche limite dans les tuyères propulsives Shock-induced flow separation in an overexpanded supersonic planar nozzle A parallel high-order compressible flows solver with domain decomposition method in the generalized curvilinear coordinates system Analysis of shock-wave unsteadiness in conical supersonic nozzles." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR06.
Повний текст джерелаThe need for a better understanding of the driving mechanism for the observed low-frequency unsteadiness in an over-expanded nozzle flows was discussed. The unsteady character of the shock wave/boundary layer remains an important practical challenge for the nozzle flow problems. Additionally, for a given incoming turbulent boundary layer, this kind of flow usually exhibits higher low-frequency shock motions which are less coupled from the timescales of the incoming turbulence. This may be good from an experimenter’s point of view, because of the difficulties in measuring higher frequencies, but it is more challenging from a computational point of view due to the need to obtain long time series to resolve low-frequency movements. In excellent agreement with the experimental findings, a very-long LES simulation run was carried out to demonstrate the existence of energetic broadband low-frequency motions near the separation point. Particular efforts were done in order to avoid any upstream low-frequency forcing, and it was explicitly demonstrated that the observed low-frequency shock oscillations were not connected with the inflow turbulence generation, ruling out the possibility of a numerical artefact. Different methods of spectral analysis and dynamic mode decomposition have been used to show that the timescales involved in such a mechanism are about two orders of magnitude larger than the time scales involved in the turbulence of the boundary layer, which is consistent with the observed low-frequency motions. Furthermore, those timescales were shown to be strongly modulated by the amount of reversed flow inside the separation bubble. This scenario can, in principle, explain both the low-frequency unsteadiness and its broadband nature
Feng, Tseng Kou, and 曾國峰. "Image Source Modeling Using High-Order Conditional Statistic Criterions." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/36405449605332620422.
Повний текст джерелаHeidkamp, Holger [Verfasser]. "Modeling localization and failure with high order finite elements / Holger Heidkamp." 2007. http://d-nb.info/985218177/34.
Повний текст джерелаKuo, Chia-Hsu T., and 郭家旭. "HIGH-ORDER SOURCE MODELING AND CODING FOR NOISELESS DATA COMPRESSION SYSTEM." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/65481007419117753380.
Повний текст джерела國立中央大學
電機工程研究所
83
The modern paradigm for data compression is to separate compression system into source modeling and sequence coding units. In this dissertation, data compression system with applications to texts including Chinese and English and gray scale images is investigated. An optimal modeling technique for Chinese text compression is established. The performance using the nibble symbol based on the higher order (n=3) outperforms that using the byte symbol with order equal to one under the same complexity. An alphabet reduction model, i.e., the bitplanes decomposition, based on different template searching algorithms is proposed to compress the gray scale images in which conditional entropy coding using high-order conditional statistics is involved. For the purpose of further reducing the resulted code rate in the lower significant bitplanes, a bitplane merging algorithm is applied to the alphabet reduction model with bitplanes decomposition owing to the high uncertainty. The compression efficiency even under the lower complexity can beat that of bitplanes decomposition without merging algorithm. We introduce a novel code table reduction with estimated conditional probabilities algorithm applied to bitplanes decomposition technique of alphabet reduction model for high-order conditional entropy coding. The serious problem of high complexity in the data compression system when the high- order conditional entropy coding is applied and the number of conditional states becomes extremely large can be untangled by this technique without the complicated incremental tree extension algorithm. Two new algorithms for repetition finder used with dynamic Huffman coding are proposed to improve the compression efficiency by reducing the redundancy due to string repetitions. The perfect results are presented in our experiments.