scholarly journals Multi space RB preconditioners for large-scale parametrized PDEs parametrized PDEs

2018 ◽  
Author(s):  
Niccolò Dal Santo
Keyword(s):  
Large Scale ◽  
State Of The Art ◽  
Navier Stokes ◽  
Reduced Basis ◽  
Fine Grid ◽  
Reduction Techniques ◽  
Efficient Construction ◽  
Short Time ◽  
Proper Orthogonal

We introduce a new two-level preconditioner for the efficient solution of large scale linear systems arising from the finite element (FE) discretization of parametrized unsteady Navier-Stokes (NS) equations. The proposed preconditioner combines a reduced basis (RB) solver, which plays the role of coarse component, with a fine grid preconditioner, in our numerical experiments a SIMPLE preconditioner. The RB coarse component is iteration dependent and is built upon a new Multi Space Reduced Basis (MSRB) method, where a RB space is built through the proper orthogonal decomposition algorithm and is tailored to each step of the iterative method at hand. The resulting operator is used as preconditioner in the flexible GMRES method. The Krylov iterations employed to solve the resulting preconditioned system target small tolerances with a very small iteration count and in a very short time. We show in this poster how to address the well-posedness of the RB coarse components and the efficient construction of the resulting preconditioner by means of hyper-reduction techniques. Simulations are carried out to evaluate the performance of the proposed MSRB preconditioner in a large scale computational setting related to the NS equations in parametrized carotid bifurcations and compared to state of the art preconditioners.

scholarly journals Trust in multi-agent systems

2004 ◽  
Vol 19 (1) ◽  
pp. 1-25 ◽  
Author(s):  
SARVAPALI D. RAMCHURN ◽  
DONG HUYNH ◽  
NICHOLAS R. JENNINGS
Keyword(s):  
Large Scale ◽  
State Of The Art ◽  
Comprehensive Treatment ◽  
Multi Agent Systems ◽  
Agent Based ◽  
Agent Systems ◽  
The Core ◽  
Open Distributed Systems ◽  
Multi Agent

Trust is a fundamental concern in large-scale open distributed systems. It lies at the core of all interactions between the entities that have to operate in such uncertain and constantly changing environments. Given this complexity, these components, and the ensuing system, are increasingly being conceptualised, designed, and built using agent-based techniques and, to this end, this paper examines the specific role of trust in multi-agent systems. In particular, we survey the state of the art and provide an account of the main directions along which research efforts are being focused. In so doing, we critically evaluate the relative strengths and weaknesses of the main models that have been proposed and show how, fundamentally, they all seek to minimise the uncertainty in interactions. Finally, we outline the areas that require further research in order to develop a comprehensive treatment of trust in complex computational settings.

Highly selective Suzuki reaction catalysed by a molecular Pd-P-MOF catalyst under mild conditions: role of ligands and palladium speciation

2022 ◽  
Author(s):  
Daniele Cartagenova ◽  
Stephan Bachmann ◽  
Kurt Püntener ◽  
Michelangelo Scalone ◽  
Mark A Newton ◽  
...  
Keyword(s):  
Large Scale ◽  
State Of The Art ◽  
Suzuki Reaction ◽  
Cross Coupling ◽  
Palladium Complexes ◽  
Fine Chemicals ◽  
Coupling Reactions ◽  
Mild Conditions ◽  
Cross Coupling Reactions

Cross-coupling reactions are a fundamental tool in the large scale synthesis of pharma-, agro- and fine chemicals. Homogeneous palladium complexes remain the state-of-the-art catalysts even though the use of heterogeneous...

scholarly journals A numerical investigation of multi space reduced basis preconditioners for parametrized elliptic advection-diffusion equations

2017 ◽  
Vol 8 (1) ◽  
pp. 282-297
Author(s):  
Niccolò Dal Santo ◽  
Simone Deparis ◽  
Andrea Manzoni
Keyword(s):  
Iterative Method ◽  
Numerical Investigation ◽  
Reduced Basis ◽  
Fine Grid ◽  
Current State ◽  
Advection Diffusion ◽  
Numerical Performance ◽  
Preconditioned Iterative ◽  
The Impact

AbstractWe analyze the numerical performance of a preconditioning technique recently proposed in [1] for the efficient solution of parametrized linear systems arising from the finite element (FE) discretization of parameterdependent elliptic partial differential equations (PDEs). In order to exploit the parametric dependence of the PDE, the proposed preconditioner takes advantage of the reduced basis (RB) method within the preconditioned iterative solver employed to solve the linear system, and combines a RB solver, playing the role of coarse component, with a traditional fine grid (such as Additive Schwarz or block Jacobi) preconditioner. A sequence of RB spaces is required to handle the approximation of the error-residual equation at each step of the iterative method at hand, whence the name of Multi Space Reduced Basis (MSRB) method. In this paper, a numerical investigation of the proposed technique is carried on in the case of a Richardson iterative method, and then extended to the flexible GMRES method, in order to solve parameterized advection-diffusion problems. Particular attention is payed to the impact of anisotropic diffusion coefficients and (possibly dominant) transport terms on the proposed preconditioner, by carrying out detailed comparisons with the current state of the art algebraic multigrid preconditioners.

Convective Heat Transfer in Turbulent Flow Near a Gap

2006 ◽  
Vol 128 (7) ◽  
pp. 701-708 ◽  
Author(s):  
D. Chang ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Vortical Structures

Convective heat transfer in a rectangular duct containing a heated rod forming a narrow gap with a plane wall has been simulated by solving the unsteady Reynolds-averaged Navier-Stokes equations with a Reynolds stress model. Of particular interest is the role of quasi-periodic coherent structures in transporting fluid and heat across the gap region. It is shown that the local instantaneous velocity and temperature vary widely because of large-scale transport by coherent vortical structures forming in pairs on either side of the rod.

scholarly journals Properties of Dust in Giant Elliptical Galaxies: The rôle of the Environment

2000 ◽  
Vol 174 ◽  
pp. 74-80
Author(s):  
Paul Goudfrooij
Keyword(s):  
Large Scale ◽  
Elliptical Galaxies ◽  
Short Time Scale ◽  
X Ray ◽  
Hot Gas ◽  
The Galaxy ◽  
The Masses ◽  
Short Time ◽  
Galaxy Nucleus

AbstractThe properties of dust in giant elliptical galaxies are reviewed, with particular emphasis on the influence of the environment.After normalizing by the optical luminosities, a strong anticorrelation between the masses of dust and hot gas in X-ray bright ellipticals is found. Furthermore, large-scale, regularly-shaped dust lanes (which are symmetric with respect to the galaxy nucleus) are only found to be present in ellipticals with the lowest ratios of the mass of hot gas to the blue luminosity (Mhot/LB ≲ 0.04 in solar units). This can be explained by the short time scale for the destruction of dust grains within the hot, X-ray- emitting gas compared to the formation timescale of such dust lanes in early-type galaxies.Dust within ellipticals in “loose” environments (i.e. in the field or in loose groups) is typically characterized by small values of RV ≡ AV/EB−V (i-e. small characteristic grain sizes), and distributed in dust lanes with a smooth, relaxed morphology. On the other hand, dust in ellipticals that are in or near the center of dense groups or clusters is typically much more irregularly distributed, and characterized by RV values that are close to the Galactic one.I predict that ellipticals containing “relaxed” dust lanes with typical dust masses of 106 − 107M⊙ do not contain hot, X-ray-emitting gas.

scholarly journals YURI SHEVELIOV IN THE PROCESSES OF CONSOLIDATION OF UKRAINIAN INTELLIGENTSIIA DURING THE PERIOD OF UKRAINIAN ART MOVEMENT ACTIVITY

2018 ◽  
pp. 118-123
Author(s):  
Serhiy Denysiuk
Keyword(s):  
Large Scale ◽  
Scientific Activity ◽  
Second World War ◽  
World War ◽  
Movement Activity ◽  
Literary Publishing ◽  
History Of ◽  
Short Time ◽  
Second World

In article is investigated role of famous Ukrainian scientist Yu. Shevelоv in the creation and activities of the unification of Ukrainian writers on emigration after the Second World War – Ukrainian Art Movement (1945-1948). The focus is on those events that Yu. Shevelоv together with his associates conducted for the organization of diverse forces of the Ukrainian creative intelligentsia in difficult conditions of separation from the Motherland.It is proved that the researcher pledged special hopes on the national-organic style as a consolidating factor of Ukrainian literary and artistic life. His main provisions are Yu. Shevelоv as one of the leading ideologues of UAM developed during the existence of this association. The idea of a national-organic style triggered a heated discussion in the Ukrainian emigration environment. The essence is highlighted differences in views on the national-organic style between Yu. Shevelov and his opponents is highlighted, the most famous of which was Volodymyr Derzhavin. It is noted large extent thanks to the efforts of Yu. Shevelov, the Ukrainian Art Movement activity in a relatively short time launched a large-scale literary, publishing and scientific activity and became an important milestone in the history of Ukrainian culture. Y. Shevelov had no doubt, that Ukraine have been always recognized as a part of Europe. But primitive mechanical imitation of foreign samples leads only to provinciality, because the main point of the province is, that it doesn’t create, but follows the capital. It is important, that, in searching internal unity of Ukrainian art and Ukrainian nation, Y. Shevelov suggested his own conception of national-organic style and tried to convince others of his truth. All activity of Y. Shevelov during the period of existence of Ukrainian Art Movement have been directed on uniting of different literary currents, trends and writers to create modern Ukrainian literature, which could satisfy with the modern requirements.

scholarly journals A Three-Dimensional Navier-Stokes Calculation Applied to an Axial Compressor Rotor and Stator

1993 ◽  
Author(s):  
Robert P. Dring ◽  
Ricky J. VanSeters ◽  
Robert M. Zacharias
Keyword(s):  
Total Pressure ◽  
Large Scale ◽  
State Of The Art ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Measured Data ◽  
Navier Stokes ◽  
Second Stage ◽  
Compressor Rotor ◽  
Pressure Distributions

The objective of this paper is to apply a three-dimensional Navier-Stokes calculation to the second stage rotor and stator of a large scale compressor and to compare the computed results with measured data. The comparisons include: (1) airfoil and endwall surface streamlines, (2) radial-circumferential distributions of exit total pressure, (3) spanwise distributions of circumferentially averaged inlet and exit flow quantities, and (4) fullspan airfoil pressure distributions. This assessment demonstrates that the computational state-of-the-art has advanced to a point where calculations such as this can be applied with reasonable confidence in both design and analysis situations.

ON THE UNIVERSAL CHARACTER OF THE LARGE SCALE STRUCTURE OF THE UNIVERSE

1992 ◽  
Vol 01 (02) ◽  
pp. 303-333 ◽  
Author(s):  
MAREK DEMIAŃSKI ◽  
ANDREJ G. DOROSHKEVICH
Keyword(s):  
Large Scale ◽  
Gravitational Instability ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Inertial Instability ◽  
Point Correlation ◽  
The Universe

We review different theories on the formation of the large scale structure of the Universe. Special emphasis is put on the theory of inertial instability. We show that, for a large class of initial spectra, the resulting two point correlation functions are similar. We also discuss the adhesion theory which uses the Burgers equation, Navier-Stokes equation or coagulation process. We review the Zeldovich theory of gravitational instability and discuss the internal structure of pancakes. Finally, we discuss the role of the velocity potential in determining the global characteristics of large scale structure (distribution of caustics, scale of voids, etc.). In the last section, we list the main unsolved problems and the main successes of the theory of formation of large scale structure.

scholarly journals Coupling finite elements and reduced approximation bases

2009 ◽  
pp. 445-463
Author(s):  
Amine Ammar ◽  
Etienne Pruliere ◽  
Julien Férec ◽  
Francisco Chinesta ◽  
Elias Cueto
Keyword(s):  
Degrees Of Freedom ◽  
Linear Models ◽  
Orthogonal Decomposition ◽  
The Other ◽  
Inverse Identification ◽  
Reduced Basis ◽  
Reduction Techniques ◽  
Separated Representations ◽  
Proper Orthogonal ◽  
Simulation Time

Models encountered in computational physics and engineering, usually involve too many degrees of freedom, too many simulation time-steps, too many iterations (e.g. non-linear models, optimization or inverse identification…), or simply excessive simulation time (for example when simulation in real time is envisaged). In some of our former works different reduction techniques were developed, some of them based on the use of an adaptive proper orthogonal decomposition and the other ones based on the use of separated representations. In this paper we are analyzing the coupling between reduced basis and standard finite element descriptions.

scholarly journals A Semi-exact Algorithm for Quickly Computing A Maximum Weight Clique in Large Sparse Graphs

2021 ◽  
Vol 72 ◽  
pp. 39-67
Author(s):  
Shaowei Cai ◽  
Jinkun Lin ◽  
Yiyuan Wang ◽  
Darren Strash
Keyword(s):  
Large Scale ◽  
Heuristic Algorithms ◽  
State Of The Art ◽  
Exact Algorithm ◽  
Exact Algorithms ◽  
Maximum Weight ◽  
Large Graphs ◽  
Sparse Graphs ◽  
Short Time ◽  
Maximum Weight Clique

This paper explores techniques to quickly solve the maximum weight clique problem (MWCP) in very large scale sparse graphs. Due to their size, and the hardness of MWCP, it is infeasible to solve many of these graphs with exact algorithms. Although recent heuristic algorithms make progress in solving MWCP in large graphs, they still need considerable time to get a high-quality solution. In this work, we focus on solving MWCP for large sparse graphs within a short time limit. We propose a new method for MWCP which interleaves clique finding with data reduction rules. We propose novel ideas to make this process efficient, and develop an algorithm called FastWClq. Experiments on a broad range of large sparse graphs show that FastWClq finds better solutions than state-of-the-art algorithms while the running time of FastWClq is much shorter than the competitors for most instances. Further, FastWClq proves the optimality of its solutions for roughly half of the graphs, all with at least 105 vertices, with an average time of 21 seconds.

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