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Literatura académica sobre el tema "Schéma Dissipatif"

Autor: Grafiati

Publicado: 30 de noviembre de 2024

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Artículos de revistas sobre el tema "Schéma Dissipatif"

Després, Bruno y Frédéric Lagoutière. "Un schéma non linéaire anti-dissipatif pour l'équation d'advection linéaire". Comptes Rendus de l'Académie des Sciences - Series I - Mathematics 328, n.º 10 (mayo de 1999): 939–43. http://dx.doi.org/10.1016/s0764-4442(99)80301-2.

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Mamouri, Saïd y Adnan Ibrahimbegovic. "Schéma dissipatif HHT d'intégration temporelle pour un modèle de poutre en grandes rotations". Revue Européenne des Éléments Finis 10, n.º 5 (enero de 2001): 607–23. http://dx.doi.org/10.1080/12506559.2001.9737562.

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Huang, Shiyi y Zhixue Li. "Optimization and Application of Coal Pillar in Fully Mechanized Mining Face based on Energy Analysis". International Journal of Energy 3, n.º 3 (1 de diciembre de 2023): 47–51. http://dx.doi.org/10.54097/ije.v3i3.011.

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Based on the theory of energy dissipation, a numerical model of goaf excavation was established by FLAC3D based on the backflow channel of Heilong Coal Industry 2202. The dissipative energy distribution characteristics of coal pillars with different widths were studied, and the dissipative energy evolution law of surrounding rock of goaf roadway was analyzed. With the increase of the width of coal pillar, the width of elastic core zone is positively correlated with the bearing capacity. The peak value of dissipated energy density decreases with the increase of the width of coal pillar, and the concentration degree and region of dissipated energy density on the side of coal pillar are greater than that on the side of solid coal pillar. The project is applied to Heilong 2201 working face, and the optimum width of coal pillar and its supporting scheme are given. The practice results show that when the width of coal pillar is 5m, the deformation of surrounding rock can be effectively controlled and the demand for safe and efficient production can be met.

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Chen, Xiaowei, Mingzhan Song y Songhe Song. "A Fourth Order Energy Dissipative Scheme for a Traffic Flow Model". Mathematics 8, n.º 8 (28 de julio de 2020): 1238. http://dx.doi.org/10.3390/math8081238.

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We propose, analyze and numerically validate a new energy dissipative scheme for the Ginzburg–Landau equation by using the invariant energy quadratization approach. First, the Ginzburg–Landau equation is transformed into an equivalent formulation which possesses the quadratic energy dissipation law. After the space-discretization of the Fourier pseudo-spectral method, the semi-discrete system is proved to be energy dissipative. Using diagonally implicit Runge–Kutta scheme, the semi-discrete system is integrated in the time direction. Then the presented full-discrete scheme preserves the energy dissipation, which is beneficial to the numerical stability in long-time simulations. Several numerical experiments are provided to illustrate the effectiveness of the proposed scheme and verify the theoretical analysis.

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Burkhardt, Ulrike y Erich Becker. "A Consistent Diffusion–Dissipation Parameterization in the ECHAM Climate Model". Monthly Weather Review 134, n.º 4 (1 de abril de 2006): 1194–204. http://dx.doi.org/10.1175/mwr3112.1.

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Abstract The diffusion–dissipation parameterizations usually adopted in GCMs are not physically consistent. Horizontal momentum diffusion, applied in the form of a hyperdiffusion, does not conserve angular momentum and the associated dissipative heating is commonly ignored. Dissipative heating associated with vertical momentum diffusion is often included, but in a way that is inconsistent with the second law of thermodynamics. New, physically consistent, dissipative heating schemes due to horizontal diffusion (Becker) and vertical diffusion (Becker, and Boville and Bretherton) have been developed and tested. These schemes have now been implemented in 19- and 39-level versions of the ECHAM4 climate model. The new horizontal scheme requires the replacement of the hyperdiffusion with a ∇2 scheme. Dissipation due to horizontal momentum diffusion is found to have maximum values in the upper troposphere/lower stratosphere in midlatitudes and in the winter hemispheric sponge layer, resulting in a warming of the area around the tropopause and of the polar vortex in Northern Hemispheric winter. Dissipation associated with vertical momentum diffusion is largest in the boundary layer. The change in parameterization acts to strengthen the vertical diffusion and therefore the associated dissipative heating. Dissipation due to vertical momentum diffusion has an indirect effect on the upper-tropospheric/stratospheric temperature field in northern winter, which is to cool and strengthen the northern polar vortex. The warming in the area of the tropopause resulting from the change in both dissipation parameterizations is quite similar in both model versions, whereas the response in the temperature of the northern polar vortex depends on the model version.

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HANSEN, JAKOB, ALEXEI KHOKHLOV y IGOR NOVIKOV. "PROPERTIES OF FOUR NUMERICAL SCHEMES APPLIED TO A NONLINEAR SCALAR WAVE EQUATION WITH A GR-TYPE NONLINEARITY". International Journal of Modern Physics D 13, n.º 05 (mayo de 2004): 961–82. http://dx.doi.org/10.1142/s021827180400502x.

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We study stability, dispersion and dissipation properties of four numerical schemes (Itera-tive Crank–Nicolson, 3rd and 4th order Runge–Kutta and Courant–Fredrichs–Levy Nonlinear). By use of a Von Neumann analysis we study the schemes applied to a scalar linear wave equation as well as a scalar nonlinear wave equation with a type of nonlinearity present in GR-equations. Numerical testing is done to verify analytic results. We find that the method of lines (MOL) schemes are the most dispersive and dissipative schemes. The Courant–Fredrichs–Levy Nonlinear (CFLN) scheme is most accurate and least dispersive and dissipative, but the absence of dissipation at Nyquist frequency, if fact, puts it at a disadvantage in numerical simulation. Overall, the 4th order Runge–Kutta scheme, which has the least amount of dissipation among the MOL schemes, seems to be the most suitable compromise between the overall accuracy and damping at short wavelengths.

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Li, Guodong, Haifeng Zhang, Xingnan Li, Lihao Guo, Yanyan Gao y Dandan Cai. "Numerical Simulation of Stepped Spillways with Front Step Deformation". Mathematical Problems in Engineering 2021 (29 de marzo de 2021): 1–15. http://dx.doi.org/10.1155/2021/7079606.

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In order to solve the flood discharge problem of both small- and medium-sized warping dams in the Loess Plateau, a stepped spillway scheme, based on an ecological bag, to achieve full-section water flow and energy dissipation has been proposed in this paper. The hydraulic and energy dissipation characteristics of a stepped spillway layout scheme were studied using 3D numerical simulation. As the height of the dams is low and the spillways are short, the research has shown that the traditional single-step layout scheme leads to a low overall energy dissipation rate due to the small amount of energy dissipated in the initial steps. As a result of this, this paper has put forward two kinds of step layout schemes such as the shunt type and the staggered type for the initial steps. Through analysis of the flow state, the pressure distribution, and the total energy dissipation rate, the results have shown that shunt type and staggered type with front step deformation produced an obvious mixing of the water flow, fewer negative pressure areas, and a higher energy dissipation rate. The optimal energy dissipation rate of the staggered type reached 87.75%, and the maximum energy dissipation rate was increased by 27.97%.

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Lin, F. B. y F. Sotiropoulos. "Assessment of Artificial Dissipation Models for Three-Dimensional Incompressible Flow Solutions". Journal of Fluids Engineering 119, n.º 2 (1 de junio de 1997): 331–40. http://dx.doi.org/10.1115/1.2819138.

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Various approaches for constructing artificial dissipation terms for three-dimensional artificial compressibility algorithms are presented and evaluated. Two, second-order accurate, central-differencing schemes, with explicitly added scalar and matrix-valued fourth-difference artificial dissipation, respectively, and a third-order accurate flux-difference splitting upwind scheme are implemented in a multigrid time-stepping procedure and applied to calculate laminar flow through a strongly curved duct. Extensive grid-refinement studies are carried out to investigate the grid sensitivity of each discretization approach. The calculations indicate that even the finest mesh employed, consisting of over 700,000 grid nodes, is not sufficient to establish grid independent solutions. However, all three schemes appear to converge toward the same solution as the grid spacing approaches zero. The matrix-valued dissipation scheme introduces the least amount of artificial dissipation and should be expected to yield the most accurate solutions on a given mesh. The flux-difference splitting upwind scheme, on the other hand, is more dissipative and, thus, particularly sensitive to grid resolution, but exhibits the best overall convergence characteristics on grids with large aspect ratios.

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Zhang, Yang, Laiping Zhang, Xin He y Xiaogang Deng. "An Improved Second-Order Finite-Volume Algorithm for Detached-Eddy Simulation Based on Hybrid Grids". Communications in Computational Physics 20, n.º 2 (21 de julio de 2016): 459–85. http://dx.doi.org/10.4208/cicp.190915.240216a.

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AbstractA hybrid grid based second-order finite volume algorithm has been developed for Detached-Eddy Simulation (DES) of turbulent flows. To alleviate the effect caused by the numerical dissipation of the commonly used second order upwind schemes in implementing DES with unstructured computational fluid dynamics (CFD) algorithms, an improved second-order hybrid scheme is established through modifying the dissipation term of the standard Roe's flux-difference splitting scheme and the numerical dissipation of the scheme can be self-adapted according to the DES flow field information. By Fourier analysis, the dissipative and dispersive features of the new scheme are discussed. To validate the numerical method, DES formulations based on the two most popular background turbulence models, namely, the one equation Spalart-Allmaras (SA) turbulence model and the two equationk–ωShear Stress Transport model (SST), have been calibrated and tested with three typical numerical examples (decay of isotropic turbulence, NACA0021 airfoil at 60° incidence and 65° swept delta wing). Computational results indicate that the issue of numerical dissipation in implementing DES can be alleviated with the hybrid scheme, the resolution for turbulence structures is significantly improved and the corresponding solutions match the experimental data better. The results demonstrate the potentiality of the present DES solver for complex geometries.

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Zhao, Peng y Yu Chuan Bai. "Study on Hydraulic Characteristics and Optimization of Siphon Channel with Two Inlets in Drydock". Applied Mechanics and Materials 638-640 (septiembre de 2014): 1285–92. http://dx.doi.org/10.4028/www.scientific.net/amm.638-640.1285.

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Compared with the siphon channel with one inlet, the siphon channel with two inlets has some problems such as low efficiency of flooding. Combining with the model test of siphon channel with two inlets in a drydock, three-dimensional numerical model was built to study the hydraulic characteristics of siphon channel system. The reliability of numerical model was confirmed by comparing the calculated value and measured value of hump pressure and flooding rate. Results of turbulent kinetic energy and dissipation rate indicate that flow kinetic energy is mainly dissipated by the friction and its impacting the wall behind partition and the effect of energy dissipation pillars are not obvious. By comparing flow state in front of energy dissipation section and flooding rate between design scheme and modified scheme, it is suggested that the guide wall should be dismantled to ameliorate flow state.

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Tesis sobre el tema "Schéma Dissipatif"

Megdich, Nadia. "Méthodes anti-dissipatives pour les équations Hamilton Jacobi Bellman". Paris 6, 2008. http://www.theses.fr/2008PA066073.

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On étudie la convergence d'un schéma anti-dissipatif, l'UltraBee, pour les équations Hamilton Jacobi Bellman en dimension 1. Deux méthodes de résolution utilisant ce schéma sont proposées. La première combine l'UltraBee à une adaptation de grille, la deuxième utilise un stockage creux. Cette dernière est appliquée au problème de la rentrée atmosphérique. Enfin, quelques extensions théoriques sont données.

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Bensaid, Bilel. "Analyse et développement de nouveaux optimiseurs en Machine Learning". Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0218.

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Ces dernières années, l’intelligence artificielle (IA) est confrontée à deux défis majeurs (parmi d’autres), à savoir l’explicabilité et la frugalité, dans un contexte d’intégration de l’IA dans des systèmes critiques ou embarqués et de raréfaction des ressources. Le défi est d’autant plus conséquent que les modèles proposés apparaissent commes des boîtes noires étant donné le nombre faramineux d’hyperparamètres à régler (véritable savoir-faire) pour les faire fonctionner. Parmi ces paramètres, l’optimiseur ainsi que les réglages qui lui sont associés ont un rôle critique dans la bonne mise en oeuvre de ces outils [196]. Dans cette thèse, nous nous focalisons sur l’analyse des algorithmes d’apprentissage/optimiseurs dans le contexte des réseaux de neurones, en identifiant des propriétés mathématiques faisant écho aux deux défis évoqués et nécessaires à la robustesse du processus d’apprentissage. Dans un premier temps, nous identifions des comportements indésirables lors du processus d’apprentissage qui vont à l’encontre d’une IA explicable et frugale. Ces comportements sont alors expliqués au travers de deux outils: la stabilité de Lyapunov et les intégrateurs géométriques. Empiriquement, la stabilisation du processus d’apprentissage améliore les performances, autorisant la construction de modèles plus économes. Théoriquement, le point de vue développé permet d’établir des garanties de convergence pour les optimiseurs classiquement utilisés dans l’entraînement des réseaux. La même démarche est suivie concernant l’optimisation mini-batch où les comportements indésirables sont légions: la notion de splitting équilibré est alors centrale afin d’expliquer et d’améliorer les performances. Cette étude ouvre la voie au développement de nouveaux optimiseurs adaptatifs, issus de la relation profonde entre optimisation robuste et schémas numériques préservant les invariants des systèmes dynamiques
Over the last few years, developping an explainable and frugal artificial intelligence (AI) became a fundamental challenge, especially when AI is used in safety-critical systems and demands ever more energy. This issue is even more serious regarding the huge number of hyperparameters to tune to make the models work. Among these parameters, the optimizer as well as its associated tunings appear as the most important leverages to improve these models [196]. This thesis focuses on the analysis of learning process/optimizer for neural networks, by identifying mathematical properties closely related to these two challenges. First, undesirable behaviors preventing the design of explainable and frugal networks are identified. Then, these behaviors are explained using two tools: Lyapunov stability and geometrical integrators. Through numerical experiments, the learning process stabilization improves the overall performances and allows the design of shallow networks. Theoretically, the suggested point of view enables to derive convergence guarantees for classical Deep Learning optimizers. The same approach is valuable for mini-batch optimization where unwelcome phenomenons proliferate: the concept of balanced splitting scheme becomes essential to enhance the learning process understanding and improve its robustness. This study paves the way to the design of new adaptive optimizers, by exploiting the deep relation between robust optimization and invariant preserving scheme for dynamical systems

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Mahéo, Laurent. "Etude des effets dissipatifs de différents schémas d'intégration temporelle en calcul dynamique par éléments finis". Phd thesis, Université de Bretagne Sud, 2006. http://tel.archives-ouvertes.fr/tel-00139112.

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Cette étude aborde différents schémas d'intégration temporelle en calcul dynamique, et leur capacité à dissiper les hautes fréquences numériques introduites par les discrétisation temporelle et spatiale. La discrétisation temporelle d'un problème de dynamique peut être réalisée par la Méthode des Différences Finies ou celle des Eléments Finis et plus particulièrement la méthode de Galerkin - discontinue. Les résultats sont alors perturbés par des oscillations parasites d'origine purement numérique et issues des discrétisations temporelle et spatiale. Des méthodes permettent de les amortir en dissipant de l'énergie. Les schémas explicites amortissants de Tchamwa - Wielgosz et de Bonelli sont tout d'abord comparés au traditionnel Bulk-viscosity sur des cas 1D et 3D axi-symétriques. Un algorithme de pilotage de l'amortissement pour le schéma de Tchamwa - Wielgosz est ensuite développé de manière à obtenir une efficacité amortissante optimale tout au long des calculs sans pour autant observer une baisse trop importante de l'énergie. L'utilisation des méthodes amortissantes sur des exemples numériques issus d'essais expérimentaux (essais aux Barres de Hopkinson, impact transversal d'une tôle) est enfin étudiée. Des conclusions de cette étude, citons tout d'abord que l'utilisation des méthodes amortissantes s'avère très efficace pour filtrer les oscillations parasites mais en dissipant généralement trop d'énergie, ce qui a motivé le développement d'un pilotage original de l'amortissement. Une seconde innovation réside dans l'étude d'un schéma temporel explicite de type éléments finis permettant d'aboutir à des résultats se rapprochant de la solution théorique discrétisée.

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Mahéo, Laurent. "Étude des effets dissipatifs de différents schémas d'intégration temporelle en calcul dynamique par éléments finis". Lorient, 2006. http://www.theses.fr/2006LORIS082.

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Cette étude aborde différents schémas d’intégration temporelle utilisés en calcul dynamique, et leur capacité à dissiper les hautes fréquences numériques introduites par les discrétisation temporelle et spatiale. La discrétisation temporelle d’un problème de dynamique peut être réalisée par la Méthode des Différences Finies (MDF) ou par la Méthode des Eléments Finis (MEF) et plus particulièrement la méthode de Galerkin-Discontinu (DG). Les résultats sont alors perturbés par des oscillations parasites d’origine purement numérique et issues des discrétisations temporelle et spatiale. Des méthodes existantes permettent de les amortir en dissipant de l’énergie. Les schémas explicites amortisssants de Tchamwa - Wielgosz et de Bonelli, issus respectivement de la discrétisation MDF et MEF sont tout d’abord comparés au traditionnel Bulk-viscosity et au schéma de Runge-Kutta d’ordre de précision 4-5 sur des cas 1D et 3D. On constate alors, grâce au cas 1D, le rôle important de la matrice masse qui conditionne le problème et l’influence du pas de temps sur l’amortissement de tous les schémas d’intégration temporelle. On remarque également que l’utilisation d’un schéma d’une précision élevée ne permet pas de s’affranchir des oscillations parasites. L’étude est ensuite menée sur un cas 3D axi-symétrique pour lequel est calculée une solution semianalytique grâce à la théorie des barres de Love. On remarque un amortissement plus faible des oscillations parasites et la dépendance de l’amortissement du Bulk-viscosity au coefficient de Poisson. L’amortissement pour ces exemples est observable plus nettement sur les contraintes transverse et de cisaillement qui sont pourvues de plus hautes fréquences que la contrainte axiale. L’utilisation des méthodes amortissantes sur des cas expérimentaux 3D comme un essai aux Barres de Hopkinson et un impact transversal sur une tôle de construction navale est enfin étudiée. L’amortissement est alors évalué sur des exemples réels complexes. On constate finalement le caractère ciblé de l’amortissement qui n’agit que sur les très hautes fréquences numériques. Un algorithme de pilotage de l’amortissement pour le schéma de Tchamwa - Wielgosz est également développé de manière à obtenir une efficacité amortissante optimale tout au long des calculs sans pour autant observer une baisse trop importante de l’énergie. Le pilotage qui permet d’individualiser l’amortissement pour chaque ddl de la structure est déterminé en fonction de deux valeurs nodales : l’accélération et la vitesse moyenne. L’algorithme est implanté dans le code de calcul universitaire Herezh++ puis étudié pour des cas 1D au maillage homogène ou non. Les résultats obtenus montrent une réelle efficacité à filtrer les hautes fréquences numériques au début du calcul et une baisse importante de la dégradation du signal de contrainte. Des conclusions de cette étude, citons tout d’abord que l’utilisation des méthodes amortissantes s’avère très efficace pour filtrer les oscillations parasites mais en dissipant, dans certains cas, trop d’énergie, ce qui a motivé le développement d’un pilotage original de l’amortissement. Une seconde innovation de ce travail réside dans l’étude d’un schéma explicite issu d’une discrétisation temporelle de type MEF permettant d’aboutir, pour un faible coût numérique, à des résultats se rapprochant de la solution théorique du système discrétisé spatialement
This phd-thesis deals with several time integration algorithms which are used in dynamic computation. The study focuses on their vibration damping properties in order to dissipate spurious oscillations generated by the use of space and time discretizations. The recents Tchamwa-Wielgosz’s explicite scheme and the Bonelli’s one are compared to the classical Bulk-viscosity method and the Runge-Kutta scheme (with a 4-5 order accuracy) for one-dimensional and three-dimensional problems. We notice the effects of the mass matrix (diagonal or consistent) and the time step size on the damping efficiency for each numerical scheme in a one-dimensional problem. We also note that the use of a high-order accuracy scheme can’t prevent the apparition of spurious oscillations. The study goes on with an axisymmetric three-dimensional problem for which we use a Love’s rods numerical solution. We note that the damping of spurious oscillations is less important in three-dimensional problems than in one-dimpensional problems. We also remark the influence of Poisson’s ratio on numerical damping when the bulk-viscosity method is used. Finally, numerical damping can be observed more easily on radial and shear stresses than on axial stresses because they are composed of the highest frequencies and consequently are more damped. The use of damping methods for three-dimensional problems, which come from experiments (Split Hopkinson Pressure Bar test and transverse impact of a steel plate), is finally studied. Therefore, damping is estimated for experimental and complex examples. Finally, we note the damping efficiency on very highfrequencies. A damping control algorithm is developed for the Tchamwa-Wielgosz’s scheme in order to obtain a damping efficiency during the whole simulation process with an energy control. Damping is realised for each degree-of-freedom of the problem and two nodal variables control the algorithm : acceleration and velocity mean. The algorithm is implemented in the HEREZH++ finite element code which is developed in C++. The results for one-dimensional problems with regular or irregular meshes show a damping efficiency at the beginning of the calculation and an energy drop less important than when a continuous damping is used. This study showed the efficiency of the damping methods to filter spurious oscillations. However, numerical damping excessively attains low-frequency modes. Thus, a new method which controls numerical damping has been developed. The second innovation deals with the study of an explicite time integration algorithm, which belongs to the Finite Element Method. This third order accuracy algorithm can approximate the theoretical solution of a discrete space for a low computational cost

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Lee, Dongwook. "An unsplit staggered mesh scheme for multidimensional magnetohydrodynamics a staggered dissipation-control differencing algorithm /". College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3842.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.
Thesis research directed by: Applied Mathematics and Scientific Computation Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Fiebach, André [Verfasser]. "A dissipative finite volume scheme for reaction-diffusion systems in heterogeneous materials / André Fiebach". Berlin : Freie Universität Berlin, 2014. http://d-nb.info/1057869732/34.

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Huart, Robin. "Simulation numérique d'écoulements magnétohydrodynamiques par des schémas distribuant le résidu". Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14480/document.

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Au cours de ce travail, nous nous sommes attaché à la résolution numérique des équations de la Magnétohydrodynamique (MHD) auxquelles s'ajoute une loi hyperbolique de transport des erreurs de divergence.La première étape consista à symétriser le nouveau système de la MHD idéale afin d'en étudier le système propre, ce qui fut l'occasion de rappeler le rôle de l'entropie au niveau de ce calcul comme à celui de l'inégalité de Clausius-Duhem. La suite de cette thèse eut pour objectif la résolution de ces équations idéales à l'aide de schémas distribuant le résidu (notés RD). Les quatre principaux schémas connus furent testés, et nous avons montré entre autres que le schéma N, qui a fait ses preuves sur les équations d'Euler en mécanique des fluides, n'était pas adapté aux équations de la MHD. Les stratégies classiques de limitation et de stabilisation purent être revisitées à ce moment. Les équations étant instationnaires, il fallut intégrer une discrétisation en temps et une distribution spatiale des termes d'évolution (et d'éventuelles sources). Nous avons d'emblée opté pour une approche implicite permettant d'être performant sur les simulations longues des expériences de tokamaks, et de traiter la correction de la divergence d'une manière originale et efficace. Les problèmes de convergence de la méthode de Newton-Raphson n'ayant pas été pleinement résolus, nous nous sommes tournés vers une alternative explicite de type Runge-Kutta. Enfin, nous avons réétabli les principes de la montée en ordre (en théorie, jusqu'à des ordres arbitraires, en prenant en compte le phénomène de Gibbs) à l'aide de tout type d'élément fini (bien construit) 2D ou 3D, sans avoir pu valider tous ces aspects. Nous avons également pris en compte les équations complètes de la MHD réelle classique (i.e. sans effet Hall) à l'aide d'un couplage RD/Galerkin
During this thesis, we worked on the numerical resolution of the Magnetohydrodynamic (MHD) equations, to which we added a hyperbolic transport equation for the divergence errors of the magnetic field.The first step consisted in symmetrizing the new ideal MHD system in order to study its eigensystem, which was the opportunity to remind the role of the entropy in this calculation as well as in the Clausius-Duhem inequality. Next, we aimed at solving these ideal equations by the mean of Residual Distribution (RD) schemes.The four main schemes were tested, and we showed among other things that the N scheme (although it has been proven very efficient with Euler equations in Fluid Mechanics) could not give satisfying results with the MHD equations. Classical strategies for the limitation and the stabilization were revisited then. Moreover,since we dealt with unsteady equations, we had to formulate atime discretization and a spatial distribution of the unsteady terms (as well as possible sources). We first choosed an implicit approach allowing us to be powerful on the long simulations needed for tokamak experiments, and to treat the divergence cleaning part in an original and efficient way. The convergence problems of our Newton-Raphson algorithm having not been fully resolved, we turned to an explicit alternative (Runge-Kutta type).Finally, we discussed about the principles of higher order schemes (theoretically, up to arbitrary orders, taking into account the Gibbs phenomenon) thanks to any type of 2D or 3D finite element (properly defined), without having been able to to validate all these aspects. We also implemented the dissipative part of the full MHD equations (in the classical sense, i.e. omitting the Hall effect) by the use of a RD/Galerkin coupling

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Broussely, Marc. "Réduction de modèles thermiques par la théorie des réseaux, application à la surveillance d'une machine asynchrone par couplage d'un modèle thermique réduit avec un schéma équivalent électrique". Poitiers, 2000. http://www.theses.fr/2000POIT2320.

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Une machine electrique est le siege de dissipations et une trop forte elevation de temperature peut entrainer un endommagement irreversible. Notre objectif est de montrer la faisabilite d'un systeme numerique de surveillance continue des temperatures et des pertes d'une machine electrique fonctionnant en temps reel. Une machine asynchrone de 5,5 kw, 4 poles a ete assemblee et equipee d'une soixantaine de thermistances, y compris au rotor, puis montee sur un banc d'essais instrumente. Un modele thermique nodal detaille d'environ 1200 nuds a ete construit suivant les plans de la machine. Le modele thermique a ete recale a partir d'essais sur la machine. Une methode originale de reduction de modeles thermiques par la theorie des reseaux a ete developpee, incluant deux etapes d'optimisation des reponses dynamiques pour le choix des nuds a conserver et pour la valeur de certains elements du modele reduit. Un schema equivalent electrique de calcul des pertes de la machine asynchrone a egalement ete developpe a partir d'un schema classique et augmente par la prise en compte de phenomenes supplementaires. Le systeme de prediction en temps reel des temperatures et des pertes a finalement ete construit par le couplage du modele thermique reduit et du modele electrique.

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Marié, Simon. "Etude de la méthode Boltzmann sur Réseau pour les simulations en aéroacoustique". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00311293.

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Ce travail de thèse s'inscrit dans une problématique visant à étudier numériquement le bruit d'origine aérodynamique généré par les écoulements turbulents autour des véhicules en utilisant la méthode Boltzmann sur Réseau (LBM). Les objectifs de cette thèse sont l'étude des capacités aéroacoustiques de la LBM ainsi que l'élaboration d'un code de calcul tridimensionnel et parallèle.
Dans un premier temps, les élements historiques et théoriques de la LBM sont présentés ainsi que le développement permettant de passer de l'équation de Boltzmann aux équations de Navier-Stokes. La construction des modèles à vitesses discrètes est également décrite. Deux modèles basés sur des opérateurs de collision différents sont présentés : le modèle LBM-BGK et le modèle LBM-MRT. Pour l'étude des capacités aéroacoustiques de la LBM, une analyse de von Neumann est réalisée pour les modèles LBM-BGK et LBM-MRT ainsi que pour l'équation de Boltzmann à vitesse discrète (DVBE). Une comparaison avec les schémas Navier-Stokes d'ordre élevé est alors menée. Pour remédier aux instabilités numériques de la méthode Boltzmann sur Réseau intervenant lors de la propagation dans des directions particulières à M>0.1, des filtres sélectifs sont utilisés et leur effet sur la dissipation est étudié.
Dans un second temps, le code de calcul L-BEAM est présenté. La structure générale et les différentes techniques de calculs sont décrites. Un algorithme de transition de résolution est développé. La modélisation de la turbulence est abordée et le modèle de Meyers-Sagaut est implémenté dans le code. Enfin, des cas tests numériques sont utilisés pour valider le code et la simulation d'un écoulement turbulent complexe est réalisée.

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Azim, Riasat. "Low-Storage Hybrid MacCormack-type Schemes with High Order Temporal Accuracy for Computational Aeroacoustics". University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1515720270119389.

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Libros sobre el tema "Schéma Dissipatif"

Brodersen, Olaf. Untersuchung einer Matrix-Dissipation in einem Zelleneckpunkt-Finite-Volumen-Schema zur Lösung der Navier-Stokes-Gleichungen. Köln: Deutsche Forschungsanstalt für Luft- und Raumfahrt, 1992.

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Yeffet, Amir. A non-dissipative staggered fourth-order accurate explicit finite difference scheme for the time-domain Maxwell's equations. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1999.

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Capítulos de libros sobre el tema "Schéma Dissipatif"

Yang, Yan. "Hybrid Scheme for Compressible MHD Turbulence". En Energy Transfer and Dissipation in Plasma Turbulence, 35–67. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-8149-2_3.

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Wen, Chih-Yung, Yazhong Jiang y Lisong Shi. "Non-dissipative Core Scheme of CESE Method". En Engineering Applications of Computational Methods, 7–19. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-0876-9_2.

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AbstractThis chapter is devoted to demonstrating the basic ideas in the CESE method. These ideas include the adoption of a space–time integral form of governing equations as the starting point of scheme construction, as well as the introduction of conservation element (CE) and solution element (SE) in the discretization of space–time domain. Then, the non-dissipative core scheme of the CESE method will be presented in detail.

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Wen, Chih-Yung, Yazhong Jiang y Lisong Shi. "CESE Schemes with Numerical Dissipation". En Engineering Applications of Computational Methods, 21–36. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-0876-9_3.

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AbstractAs depicted in Chap. 2, the interface between the two sub-CEs (CD in Fig. 2.7), belongs to the SE of (j, n). The flux FC needs to be calculated through the Taylor expansion at point (j, n) toward the inverse time direction. As a result, the a scheme is reversible. This violates the second law of thermodynamics. Thus, the non-dissipative core suffers from the unphysical oscillations for practical applications.

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Poluru, Venkata Reddy. "A Low Dissipative Scheme for Hyperbolic Conservation Laws". En Lecture Notes in Mechanical Engineering, 583–89. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-15-9956-9_57.

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Fang, Yuheng, Jianyi Shi, Zhuo Sun, Song Kong y Sese Wang. "Energy Dissipation Balance Scheme in Dynamic Ad Hoc Networks". En Proceedings of the 2015 International Conference on Communications, Signal Processing, and Systems, 77–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 2016. http://dx.doi.org/10.1007/978-3-662-49831-6_8.

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Pelanti, M., L. Quartapelle y L. Vigevano. "Low Dissipation Entropy Fix for Positivity Preserving Roe’s Scheme". En Godunov Methods, 685–90. Boston, MA: Springer US, 2001. http://dx.doi.org/10.1007/978-1-4615-0663-8_69.

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Babik, F., R. Herbin, W. Kheriji y J. C. Latché. "Discretization of the viscous dissipation term with the MAC scheme". En Finite Volumes for Complex Applications VI Problems & Perspectives, 571–79. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-20671-9_60.

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Conde Martín, S. y J. C. García Orden. "Energy-Consistent Integration Scheme for Multi-body Systems with Dissipation". En New Trends in Mechanism and Machine Science, 413–21. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-09411-3_44.

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Guo-yan, Zhao y Sun Ming-bo. "Robust and Low-Dissipation Explicit Formulation of Improved Adaptive WCNS Scheme". En 31st International Symposium on Shock Waves 1, 1191–99. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-319-91020-8_144.

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Porubov, A. V., D. Bouche y G. Bonnaud. "Compensation of the Scheme Dispersion and Dissipation by Artificial Non-linear Additions". En Transactions on Computational Science VII, 122–31. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-11389-5_7.

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Actas de conferencias sobre el tema "Schéma Dissipatif"

Hou, Daizheng, Yanfei Zhang y Yafu Zhou. "A Novel Heat Dissipation Optimization Design Scheme of Printed Circuit Board". En 2024 3rd International Conference on Energy, Power and Electrical Technology (ICEPET), 1635–41. IEEE, 2024. http://dx.doi.org/10.1109/icepet61938.2024.10627435.

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Tian, Cheng, Song Fu y Siya Jiang. "Numerical Dissipation Effects on Detached Eddy Simulation of Turbomachinery Flows". En GPPS Xi'an21. GPPS, 2022. http://dx.doi.org/10.33737/gpps21-tc-74.

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Detached eddy simulation (DES) is a high-resolution method for predicting complex unsteady flows in turbomachinery. Recent researches have shown that in DES the numerical dissipation from the spatial discretization scheme should be limited to a reasonable extent. Through the test-case of decaying isotropic turbulence, the impact of the Roe scheme is assessed with three reconstruction approaches: the 3rd-order MUSCL, the 5th-order WENO, and the 4th-order minimized dispersion and controllable dissipation (MDCD) scheme. From the results, however, even with the least dissipative 4th-order MDCD scheme, the Roe scheme possesses high numerical damping for the small-scale turbulent structures. To further decrease the dissipation, the Roe scheme is modified via an adaptive factor. This adaptive scheme has small dissipation in the LES region to capture multiscale turbulent structures and returns to the original Roe scheme near shock waves to suppress numerical oscillations. The scheme with adaptive dissipation is also used to calculate flows in a centrifugal compressor. The resolution of small vortex structures, such as the tip leakage vortices and the wake vortices, is well improved.

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Kim, Dehee y Jang Hyuk Kwon. "A Low Dissipative and Dispersive Scheme with a High Order WENO Dissipation for Unsteady Flow Analyses". En 34th AIAA Fluid Dynamics Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2004. http://dx.doi.org/10.2514/6.2004-2705.

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Su, Xinrong, Satoru Yamamoto y Xin Yuan. "On the Accurate Prediction of Tip Vortex: Effect of Numerical Schemes". En ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94660.

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This work is conducted towards the accurate prediction of compressor tip vortex. Accurate computation of highly vortical flow is affected by many parameters, such as numerical scheme and turbulence model. In this work the effect of numerical scheme is studied using mesh refinement study and comparison of numerical results from central scheme and a newly developed high order upwind scheme. Behaviors of numerical methods in the tip vortex region are also theoretically and numerically analyzed. It is found the computed tip vortex is significantly affected by mesh resolution and numerical dissipation. Currently widely numerical strategy, i.e., mesh with moderate resolution and low order scheme would yield quite inaccurate result. Predicted tip vortex is always dissipated earlier and this highlights the advantage of high order scheme in predicting detailed flow features. Besides coarser mesh and low order method, analysis of numerical methods reveals a new finding, in that the designed order of accuracy is not guaranteed in the tip vortex region. For central scheme pressure based shock sensor is unnecessarily activated and excessive artificial dissipation is added. For high order upwind scheme it tends to use low order reconstruction and new method considering flow physics shows its improved vortex prediction capability. Conclusions from this work can be used in future numerical studies about tip vortex to improve the numerical accuracy.

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Christensen, Adam y Samuel Graham. "Heat Dissipation in GaN Power Semiconductor Devices". En ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61525.

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In this work, a numerical study is presented of the impact of growth substrates on thermal dissipation in GaN devices. Substrates included in this study are sapphire, SiC, GaN, ZnO, and LiGaO2. Based on a model high power HFET device with the rear side held at a fixed temperature, the maximum junction temperature in the devices were calculated using finite element analysis and compared. Both interface resistance and the effects of dislocations in the GaN layer were accounted for. Results show that state of the art devices dissipating 10 W/mm of power must be fabricated on high thermal conductivity substrates like GaN or SiC when rear side heat dissipation is utilized. In contrast, an analysis of high heat flux removal convective cooling was investigated for the application of front side heat dissipation. These results show that junction temperatures below 150°C are readily obtainable using this method and are substrate independent. The implications of the substrate independent cooling scheme are discussed.

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Bahrainian, Seyed Saied. "Effect of Dissipative Terms on the Quality of Two and Three-Dimensional Euler Flow Solutions". En ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55221.

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The Euler equations are a set of non-dissipative hyperbolic conservation laws that can become unstable near regions of severe pressure variation. To prevent oscillations near shockwaves, these equations require artificial dissipation terms to be added to the discretized equations. A combination of first-order and third-order dissipative terms control the stability of the flow solutions. The assigned magnitude of these dissipative terms can have a direct effect on the quality of the flow solution. To examine these effects, subsonic and transonic solutions of the Euler equations for a flow passed a circular cylinder has been investigated. Triangular and tetrahedral unstructured grids were employed to discretize the computational domain. Unsteady Euler equations are then marched through time to reach a steady solution using a modified Runge-Kutta scheme. Optimal values of the dissipative terms were investigated for several flow conditions. For example, at a free stream Mach number of 0.45 strong shock waves were captured on the cylinder by using values of 0.25 and 0.0039 for the first-order and third-order dissipative terms. In addition to the shock capturing effect, it has been shown that smooth pressure coefficients can be obtained with the proper values for the dissipative terms.

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Jordan, Stephen A. "The Effects of the Boundary Stencils on the Field Spatial Resolution When Using Compact Finite Differences". En ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98049.

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When establishing the spatial resolution character of a composite compact finite differencing template for high-order field solutions, the stencils selected at non-periodic boundaries are commonly treated independent of the interior scheme. This position quantifies a false influence of the boundary scheme on the resultant interior dispersive and dissipative consequences of the compound template. Of the three ingredients inherent in the composite template, only its numerical accuracy and global stability have been properly treated in a coupled fashion. Herein, we present a companion means for quantifying the resultant spatial resolution properties. Compact boundary stencils with free parameters to minimize the field dispersion (or phase error) and dissipation are included in the proposed procedure. Application of the couples templates to Burgers equation at the non-periodic boundary showed significant differences in the predictive error.

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Pinho, Pedro V., André G. Primo, Natália C. Carvalho, Rodrigo Benevides, Cauê M. Kersul, Simon Groeblacher, Gustavo S. Wiedehecker y Thiago P. Mayer Alegre. "Quadrature-Resolved Dissipative Optomechanical Measurement". En CLEO: Fundamental Science. Washington, D.C.: Optica Publishing Group, 2023. http://dx.doi.org/10.1364/cleo_fs.2023.fth1b.2.

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Parida, Pritish R., Srinath V. Ekkad y Khai Ngo. "Novel PCM and Jet Impingement Based Cooling Scheme for High Density Transient Heat Loads". En 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22841.

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Breakthroughs in the recent cutting-edge technologies have become increasingly dependent on the ability to safely dissipate large amount of heat from small areas. Improvements in cooling techniques are therefore required to avoid unacceptable temperature rise and at the same time maintain high efficiency. Jet impingement is one such cooling scheme which has been widely used to dissipate transient and steady concentrated heat loads. With constantly increasing transient cooling needs, conventional pin-fin cooling and conventional jet impingement cooling are not meeting the requirements. Considerable improvements are therefore required to meet such stringent requirements without any significant changes in the cooling system. A combined cooling scheme based on jet impingement and phase change materials (PCMs) is presented as one such alternative to existing cooling systems. A high heat storage capability of PCMs in combination with a high heat transfer rates from impingement cooling can help overcome the existing heat distribution and transient cooling problems in high heat flux dissipating devices. Preliminary conjugate CFD simulations show promising results. Additionally, experimental validation of the simulation predictions has also been performed. A reasonably good agreement was found between the predictions and experiments.

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Primo, André G., Pedro V. Pinho, Natália C. Carvalho, Rodrigo Benevides, Cauê M. Kersul, Simon Groeblacher, Gustavo S. Wiedehecker y Thiago P. Mayer Alegre. "Homodyne Detection of Dissipative Optomechanical Interactions". En Latin America Optics and Photonics Conference. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/laop.2022.m4d.6.

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We present and validate a novel route to directly probe the dissipative optomechanical coupling in a balanced homodyne detection scheme. The ratio between dissipative and dispersive coupling is determined as G κ e / G ω ≈ − 0.007 ± 0.001 .

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