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An extended coordinate descent method for distributed anticipatory network traffic control Rinaldi, Marco ; in Transportation Research. Part B : Methodological (2015), 80 Anticipatory optimal network control can be defined as the practice of determining the set of control actions that minimizes a network-wide objective function, so that the consequences of this action are ... [more ▼] Anticipatory optimal network control can be defined as the practice of determining the set of control actions that minimizes a network-wide objective function, so that the consequences of this action are taken in consideration not only locally, on the propagation of flows, but globally, taking into account the user's routing behavior. Such an objective function is, in general, defined and optimized in a centralized setting, as knowledge regarding the whole network is needed in order to correctly compute it. This is a strong theoretical framework but, in practice, reaching a level of centralization sufficient to achieve said optimality is very challenging. Furthermore, even if centralization was possible, it would exhibit several shortcomings, with concerns such as computational speed (centralized optimization of a huge control set with a highly nonlinear objective function), reliability and communication overhead arising.The main aim of this work is to develop a decomposed heuristic descent algorithm that, demanding the different control entities to share the same information set, attains network-wide optimality through separate control actions. © 2015 Elsevier Ltd. [less ▲] Detailed reference viewed: 88 (9 UL)Die Extended Discrete Element Method (XDEM) als integraler Ansatz für reagierende Mehrphasenströmungen Peters, Bernhard ; in 26. Deutscher Flammentag Verbrennung und Feuerung (2013, September) Eine Großzahl technischer Anwendungen wie beispielsweise in der pharmazeutischen Industrie, Nahrungsmittelindustrie, Bergbau, Verfahrenstechnik oder Energiegewinnung durch Verbrennung von Feststoffen ... [more ▼] Eine Großzahl technischer Anwendungen wie beispielsweise in der pharmazeutischen Industrie, Nahrungsmittelindustrie, Bergbau, Verfahrenstechnik oder Energiegewinnung durch Verbrennung von Feststoffen enthalten neben einer gasförmigen oder fluiden Phase eine diskrete Phase in Form von Partikeln oder Feststoffen. Diese Anwendungen lassen sich sehr vorteilhaft mit dem innovativen Konzept der Extended Discrete Element Method (XDEM) numerisch beschreiben. Hierbei werden die einzelnen Partikel über den dynamischen Zustand (Position und Orientierung) und den thermodynamischen Zustand (Temperatur und Spezies) diskret beschrieben, wo hingegen die Gas- oder Flüssigphase über kontinuumsmechanische Ansätze der Computational Fluid Dynamics (CFD) berechnet wird. Beide Phasen – diskret und kontinuumsmechanisch – sind durch Austausch von Stoff, Wärme und Impuls gekoppelt, was damit eine detaillierte Auflösung der Phasen für CFD-Gesamtrechnungen ermöglicht. Dieser Ansatz wurde angewendet, um den Reaktionsprozess während der Pyrolyse von Holz in einem Festbettreaktor zu berechnen. [less ▲] Detailed reference viewed: 93 (6 UL)The extended discrete element method (XDEM) applied to drying of a packed bed Peters, Bernhard ; Besseron, Xavier ; Estupinan Donoso, Alvaro Antonio et al in Industrial Combustion (2014), 14 A vast number of engineering applications involve physics not solely of a single domain but of several physical phenomena, and therefore are referred to as multi-physical. As long as the phenomena ... [more ▼] A vast number of engineering applications involve physics not solely of a single domain but of several physical phenomena, and therefore are referred to as multi-physical. As long as the phenomena considered are to be treated by either a continuous (i.e. Eulerian) or discrete (i.e. Lagrangian) approach, numerical solution methods may be employed to solve the problem. However, numerous challenges in engineering exist and evolve; those include modelling a continuous and discrete phase simultaneously, which cannot be solved accurately by continuous or discrete approaches only. Problems that involve both a continuous and a discrete phase are important in applications as diverse as the pharmaceutical industry, the food processing industry, mining, construction, agricultural machinery, metals manufacturing, energy production and systems biology. A novel technique referred to as Extended Discrete Element Method (XDEM) has been developed that offers a significant advancement for coupled discrete and continuous numerical simulation concepts. XDEM extends the dynamics of granular materials or particles as described through the classical discrete element method (DEM) to include additional properties such as the thermodynamic state or stress/strain for each particle coupled to a continuous phase such as a fluid flow or a solid structure. Contrary to a continuum mechanics concept, XDEM aims at resolving the particulate phase through the various processes attached to particles. While DEM predicts the spatial-temporal position and orientation for each particle, XDEM additionally estimates properties such as the internal temperature and/or species distribution during drying, pyrolysis or combustion of solid fuel material such as biomass in a packed bed. These predictive capabilities are further extended by an interaction with fluid flow by heat, mass and momentum transfer and the impact of particles on structures. © International Flame Research Foundation, 2014. [less ▲] Detailed reference viewed: 98 (6 UL)The Extended Discrete Element Method (XDEM) as a Flexible and Advanced Tool in Multi-physics Applications Peters, Bernhard in 26th International Symposium on Transport Phenomena (2015) Detailed reference viewed: 47 (3 UL)The extended discrete element method (XDEM) for multi-physics applications Peters, Bernhard in Scholarly Journal of Engineering Research (2013) Detailed reference viewed: 116 (18 UL)The Extended Discrete Element Method (XDEM) for Multi-Physics Applications Peters, Bernhard Scientific Conference (2013) Detailed reference viewed: 72 (8 UL)The extended discrete element method (XDEM) for multi-physics applications Peters, Bernhard in Scholarly Journal of Engineering Research (2013), 2 The Extended Discrete Element Method (XDEM) is a novel numerical simulation technique that extends the dynamics of granular materials or particles as described through the classical Discrete Element ... [more ▼] The Extended Discrete Element Method (XDEM) is a novel numerical simulation technique that extends the dynamics of granular materials or particles as described through the classical Discrete Element Method (DEM) by additional properties such as the thermodynamic state, stress/strain, or electromagnetic field for each particle coupled to a continuum phase such as fluid flow or solid structures. Contrary to a continuum mechanics concept, XDEM aims at resolving the particulate phase through the various processes attached to particles, while DEM predicts the special-temporal position and orientation for each particle; XDEM additionally estimates properties such as the internal temperature and/or species distribution. These predictive capabilities are further extended by an interaction to fluid flow by heat, mass and momentum transfer and impact of particles on structures. These superior features as compared to traditional and pure continuum mechanic approaches are highlighted by predicted examples of relevant engineering applications. [less ▲] Detailed reference viewed: 278 (42 UL)Die Extended Discrete Element Method (XDEM) für multiphysikalische Anwendungen Peters, Bernhard ; Besseron, Xavier ; Estupinan Donoso, Alvaro Antonio et al Scientific Conference (2013) A vast number of engineering applications include a continuous and discrete phase simultaneously, and therefore, cannot be solved accurately by continuous or discrete approaches only. Problems that ... [more ▼] A vast number of engineering applications include a continuous and discrete phase simultaneously, and therefore, cannot be solved accurately by continuous or discrete approaches only. Problems that involve both a continuous and a discrete phase are important in applications as diverse as pharmaceutical industry e.g. drug production, agriculture food and processing industry, mining, construction and agricultural machinery, metals manufacturing, energy production and systems biology. <br />A novel technique referred to as Extended Discrete Element Method (XDEM) is developed, that offers a significant advancement for coupled discrete and continuous numerical simulation concepts. XDEM treats the solid phase representing the particles and the fluidised phase usually a fluid phase or a structure as two distinguished phases that are coupled through heat, mass and momentum transfer. An outstanding feature of the numerical concept is that each particle is treated as an individual entity that is described by its thermodynamic state e.g. temperature and reaction progress and its position and orientation in time and space. The thermodynamic state includes one-dimensional and transient distributions of temperature and species within the particle and therefore, allows a detailed and accurate characterisation of the reaction progress in a fluidised bed. Thus, the proposed methodology provides a high degree of resolution ranging from scales within a particle to the continuum phase as global dimensions. <br />These superior features as compared to traditional and pure continuum mechanics approaches are applied to predict drying of wood particles in a packed bed and impact of particles on a membrane. Pre- heated air streamed through the packed bed, and thus, heated the particles with simultaneous evaporation of moisture. Water vapour is transferred into the gas phase at the surface of the particles and transported to the exit of the reactor. A rather inhomogeneous drying process in the upper part of the reactor with higher temperatures around the circumference of the inner reactor wall was observed. The latter is due to increased porosity in conjunction with higher mass flow rates than in the centre of the reactor, and thus, augmented heat transfer. A comparison of the weight loss over time agreed well with measurements. <br />Under the impact of falling particles the surface of a membrane deforms that conversely affects the motion of particles on the surface. Due to an increasing vertical deformation particles roll or slide down toward the bottom of the recess, where they are collected in a heap. Furthermore, during initial impacts deformation waves are predicted that propagate through the structure, and may, already indicate resonant effects already before a prototype is built. Hence, the Extended Discrete Element Method offers a high degree of resolution avoiding further empirical correlations and extends the knowledge into the underlying physics. Although most of the work load concerning CFD and FEM is arranged in the ANSYS workbench, a complete integration is intended that allows for a smooth workflow of the entire simulation environment. [less ▲] Detailed reference viewed: 348 (30 UL)Extended Discrete Element Method (XDEM) to Model Heterogeneous Reactions in Packed Beds Hoffmann, Florian ; Peters, Bernhard in PARTEC - International Congress on Particle Technology (2013, April) Packed beds, due to their high surface-area-to-volume-ratio, are widely used for chemical reactors, such as catalytic or pebble bed reactors, blast furnaces or as heat exchanging units. Depending on the ... [more ▼] Packed beds, due to their high surface-area-to-volume-ratio, are widely used for chemical reactors, such as catalytic or pebble bed reactors, blast furnaces or as heat exchanging units. Depending on the mode of packing, structured or random, a different degree of heterogeneity is introduced. For stable and efficient process handling local quantities such as temperature or concentration of chemical species are of major interest. Direct measurement of such quantities has proven very difficult or unfeasable due to the morphology of the bed. Hence, numerical modeling can help to gain insights into inaccessible parts of such reactors. The objective of this contribution is to introduce a discrete numerical approach that describes heterogeneous reaction processes within packed and moving beds. The so-called Extended Discrete Element Method (XDEM) is used to account for convective heat and mass transfer within porous media. Both motion and chemical conversion of particulate material can be dealt with. A granular medium consists of an ensemble of particles of which each exhibits individual chemical and mechanical properties. Dynamics of solid particles is accounted for by the known discrete element approach. In addition physicochemical conversion of an individual particle like drying, gasification or redox reactions are accounted for by transient differential equations (species, energy, momentum) on a particle scale. Predictions include properties such as temperature and species distribution inside a particle. The general and modular formulation of the model allows for application to any chemical process involving heterogeneous reactions. Chemical interaction between multiple particles takes place through gaseous intermediates by heat and mass transfer. Computational Fluid Dynamics is applied for the gaseous continuum in the voidage between particles. The presented model can act as tool to gain valuable insights into chemical processes inside packed beds such as blast furnace iron making or gasification of biomass. It can serve as a toolbox for prediction, analysis and optimization of a variety of process parameters such as residence time, conversion progress, burden charging and gas flow patterns. As an example a section of the burden in a blast furnace is focused on. [less ▲] Detailed reference viewed: 260 (8 UL)eXtended Discrete Element Method used for convective heat transfer predictions Estupinan Donoso, Alvaro Antonio ; Hoffmann, Florian ; Peters, Bernhard in International Review of Mechanical Engineering (2013), 7(2), 329-336 Packed bed reactors dominate a broad range of engineering applications. In a packed bed reactor, heat is transferred from the solid particles to the gas flow stream through the void space between ... [more ▼] Packed bed reactors dominate a broad range of engineering applications. In a packed bed reactor, heat is transferred from the solid particles to the gas flow stream through the void space between particles. Using a XDEM approach, continuous and discrete phases have been coupled in order to predict convective heat transfer between solid and fluid within packed beds. For the solid matrix a discrete intra-particle model, namely DPM, was used to solve for each particle of the bed, and a CFD tool was employed to resolve the fluid flow. [less ▲] Detailed reference viewed: 307 (38 UL)eXtended Discrete Element Method used for predicting tungsten-oxide reduction in a dry-hydrogen atmosphere Estupinan Donoso, Alvaro Antonio ; Peters, Bernhard in LLanes, Luis (Ed.) eXtended Discrete Element Method used for predicting tungsten-oxide reduction in a dry-hydrogen atmosphere (2014, March 10) Detailed reference viewed: 226 (28 UL)Extended Ensembles Techniques Schilling, Tanja Presentation (2008) Detailed reference viewed: 18 (0 UL)Extended Explanatory Argumentation Frameworks Dauphin, Jérémie ; Cramer, Marcos in Theory and Applications of Formal Argumentation (2018) Multiple extensions of Dung's argumentation frameworks (AFs) have been proposed in order to model features of argumentation that cannot be directly modeled in AFs. One technique that has already ... [more ▼] Multiple extensions of Dung's argumentation frameworks (AFs) have been proposed in order to model features of argumentation that cannot be directly modeled in AFs. One technique that has already previously proven useful to study and combine such extensions is the meta-argumentation methodology involving the notion of a flattening. In order to faithfully model the interaction between explanation argumentation in scientific debates, Šešelja and Straßer have introduced Explanatory Argumentation Frameworks (EAFs). In this paper, we first prove that the flattening technique works as expected for recursive (higher-order) attacks. Then we apply this technique in order to combine EAFs with multiple other extensions that have been proposed to AFs, namely with recursive attacks, joint attacks and a support relation between arguments. This gives rise to Extended Explanatory Argumentation Frameworks (EEAFs). We illustrate the applicability of EEAFs by using them to model a piece of argumentation from a research-level philosophy book. [less ▲] Detailed reference viewed: 266 (20 UL)An extended finite element library Bordas, Stéphane ; ; et al in International Journal for Numerical Methods in Engineering (2007), 71(6), 703-732 This paper presents and exercises a general structure for an object-oriented-enriched finite element code. The programming environment provides a robust tool for extended finite element (XFEM ... [more ▼] This paper presents and exercises a general structure for an object-oriented-enriched finite element code. The programming environment provides a robust tool for extended finite element (XFEM) computations and a modular and extensible system. The programme structure has been designed to meet all natural requirements for modularity, extensibility, and robustness. To facilitate mesh-geometry interactions with hundreds of enrichment items, a mesh generator and mesh database are included. The salient features of the programme are: flexibility in the integration schemes (subtriangles, subquadrilaterals, independent near-tip, and discontinuous quadrature rules); domain integral methods for homogeneous and bi-material interface cracks arbitrarily oriented with respect to the mesh; geometry is described and updated by level sets, vector level sets or a standard method; standard and enriched approximations are independent; enrichment detection schemes: topological, geometrical, narrow-band, etc.; multi-material problem with an arbitrary number of interfaces and slip-interfaces; non-linear material models such as J2 plasticity with linear, isotropic and kinematic hardening. To illustrate the possible applications of our paradigm, we present 2D linear elastic fracture mechanics for hundreds of cracks with local near-tip refinement, and crack propagation in two dimensions as well as complex 3D industrial problems. Copyright © 2007 John Wiley & Sons, Ltd. [less ▲] Detailed reference viewed: 1000 (7 UL)Extended Finite Element Method ; Zilian, Andreas ; in International Journal for Numerical Methods in Engineering (2011), 86(4-5), 403 [No abstract available] Detailed reference viewed: 132 (3 UL)An extended finite element method (XFEM) for linear elastic fracture with smooth nodal stress ; ; Bordas, Stéphane et al in Engineering Fracture Mechanics (2014) Detailed reference viewed: 517 (4 UL)Extended finite element method for dynamic fracture of piezo-electric materials ; ; et al in Engineering Fracture Mechanics (2012), 92 We present an extended finite element formulation for dynamic fracture of piezo-electric materials. The method is developed in the context of linear elastic fracture mechanics. It is applied to mode I and ... [more ▼] We present an extended finite element formulation for dynamic fracture of piezo-electric materials. The method is developed in the context of linear elastic fracture mechanics. It is applied to mode I and mixed mode-fracture for quasi-steady cracks. An implicit time integration scheme is exploited. The results are compared to results obtained with the boundary element method and show excellent agreement. [less ▲] Detailed reference viewed: 99 (0 UL)Extended finite element method with edge-based strain smoothing (ESm-XFEM) for linear elastic crack growth ; ; Bordas, Stéphane et al in Computer Methods in Applied Mechanics and Engineering (2012), 209-212 This paper presents a strain smoothing procedure for the extended finite element method (XFEM). The resulting "edge-based" smoothed extended finite element method (ESm-XFEM) is tailored to linear elastic ... [more ▼] This paper presents a strain smoothing procedure for the extended finite element method (XFEM). The resulting "edge-based" smoothed extended finite element method (ESm-XFEM) is tailored to linear elastic fracture mechanics and, in this context, to outperform the standard XFEM. In the XFEM, the displacement-based approximation is enriched by the Heaviside and asymptotic crack tip functions using the framework of partition of unity. This eliminates the need for the mesh alignment with the crack and re-meshing, as the crack evolves. Edge-based smoothing (ES) relies on a generalized smoothing operation over smoothing domains associated with edges of simplex meshes, and produces a softening effect leading to a close-to-exact stiffness, "super-convergence" and "ultra-accurate" solutions. The present method takes advantage of both the ES-FEM and the XFEM. Thanks to the use of strain smoothing, the subdivision of elements intersected by discontinuities and of integrating the (singular) derivatives of the approximation functions is suppressed via transforming interior integration into boundary integration. Numerical examples show that the proposed method improves significantly the accuracy of stress intensity factors and achieves a near optimal convergence rate in the energy norm even without geometrical enrichment or blending correction. [less ▲] Detailed reference viewed: 123 (2 UL)Extended Finite Element Method with Global Enrichment ; ; Bordas, Stéphane et al Scientific Conference (2015, July) A variant of the extended finite element method is presented which facilitates the use of enriched elements in a fixed volume around the crack front (geometrical enrichment) in 3D fracture problems. The ... [more ▼] A variant of the extended finite element method is presented which facilitates the use of enriched elements in a fixed volume around the crack front (geometrical enrichment) in 3D fracture problems. The major problem associated with geometrical enrichment is that it significantly deteriorates the conditioning of the resulting system matrices, thus increasing solution times and in some cases making the systems unsolvable. For 2D problems this can be dealt with by employing degree of freedom gathering [1] which essentially inhibits spatial variation of enrichment function weights. However, for the general 3D problem such an approach is not possible since spatial variation of the enrichment function weights in the direction of the crack front is necessary in order to reproduce the variation of solution variables, such as the stress intensity factors, along the crack front. The proposed method solves the above problem by employing a superimposed mesh of special elements which serve as a means to provide variation of the enrichment function weights along the crack front while still not allowing variation in any other direction. The method is combined with special element partitioning algorithms [2] and numerical integration schemes [3] as well as techniques for the elimination of blending errors between the standard and enriched part of the approximation in order to further improve the accuracy of the produced results. Additionally, a novel benchmark problem is introduced which enables the computation of displacement and energy error norms as well as errors in the stress intensity factors for the general 3D case. Through this benchmark problem it is shown that the proposed method provides optimal convergence rates, improved accuracy and reduced computational cost compared to standard XFEM. [less ▲] Detailed reference viewed: 632 (10 UL)An extended finite element method with smooth nodal stress ; ; Bordas, Stéphane et al Report (n.d.) Detailed reference viewed: 113 (3 UL) |
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