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SPE Reservoir Simulation Symposium 2015

作者： Gries, Sebastian Plum, Hans-Joachim Fraunhofer Institute for Algorithms and Scientific Computing SCAI Germany

ISBN: (纸本)9781510800618

Algebraic multigrid (AMG) methods for directly solving coupled systems of partial differential equations (PDEs) have been extensively used in various types of numerical simulations in engineering. A necessary condition for its efficient applicability is the simulation process being driven by elliptic components. In reservoir simulation the pressure, described by Darcy's law, is known to drive the process and hence System-AMG should be applicable and outperform classical solvers. In the context of adaptive and fully implicit reservoir simulations, the linearization of balance equations results in linear systems of equations that can be challenging. This makes it crucial to exploit all physical information from the full system to construct a robust AMG strategy and to extend it to more complex simulations than Black-Oil. At the same time, the full set of information helps to get the best out of AMG. Just as with multigrid in general, System- AMG provides a framework for combining algorithmic modules rather than a fixed solution algorithm. The adaptation of the solution strategy to the concrete class of applications is the key to obtain the best performance. Finally, System-AMG does not only allow for choosing more efficient algorithmic strategies, but also for exploiting parallelism in an optimized way, regardless of the simulation code being parallelized or not. Because the linear solver time is typically far dominating, even serial simulators can immediately and substantially benefit from MPI parallelism. Copyright © 2015 Society of Petroleum Engineers.

关键词： Linear systems

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Preface

Lecture Notes in Computational Science and Engineering

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Lecture Notes in Computational Science and Engineering 2017年 115卷 V页

作者： Griebel, Michael Schweitzer, Marc Alexander Institut für Numerische Simulation Universität Bonn Bonn Germany Fraunhofer Institute for Algorithms and Scientific Computing SCAI Sankt Augustin Germany

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ϵ-dimension in infinite dimensional hyperbolic cross approximation and application to parametric elliptic PDEs

arXiv

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arXiv 2017年

作者： Dũng, Dinh Griebel, Michael Huy, Vu Nhat Rieger, Christian Information Technology Institute Vietnam National University Hanoi 144 Xuan Thuy Cau Giay Hanoi Viet Nam Institute for Numerical Simulation Bonn University Wegelerstrasse 6 Bonn53115 Germany Fraunhofer Institute for Algorithms and Scientific Computing Scai Schloss Birlinghoven Sankt Augustin53754 Germany College of Science Vietnam National University Hanoi 334 Nguyen Trai Thanh Xuan Hanoi Viet Nam

In this article, we present a cost-benefit analysis of the approximation in tensor products of Hilbert spaces of Sobolev-analytic type. The Sobolev part is defined on a finite dimensional domain, whereas the analytical space is defined on an infinite dimensional domain. As main mathematical tool, we use the ϵ-dimension of a subset in a Hilbert space. The ϵ-dimension gives the lowest number of linear information that is needed to approximate an element from the set in the norm of the Hilbert space up to an accuracy ϵ > 0. From a practical point of view this means that we a priori fix an accuracy and ask for the amount of information to achieve this accuracy. Such an analysis usually requires sharp estimates on the cardinality of certain index sets which are in our case infinite-dimensional hyperbolic crosses. As main result, we obtain sharp bounds of the ϵ-dimension of the Sobolev-analytic-type function classes which depend only on the smoothness differences in the Sobolev spaces and the dimension of the finite dimensional domain where these spaces are defined. This implies in particular that, up to constants, the costs of the infinite dimensional (analytical) approximation problem is dominated by the finite-variate Sobolev approximation problem. We demonstrate this procedure with an examples of functions spaces stemming from the regularity theory of parametric partial differential equations. Copyright © 2017, The Authors. All rights reserved.

关键词： Stochastic systems

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Ten simple rules for measuring the impact of workshops

arXiv

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arXiv 2018年

作者： Sufi, Shoaib Duckles, Beth Simera, Iveta Nurmikko-Fuller, Terhi Bellis, Louisa Miah, Wadud Wilde, Adriana Nenadic, Aleksandra Silva, Raniere de Beyer, Jennifer A. Struthers, Caroline Emsley, Iain Philippe, Olivier Balzano, Melissa Coelho, Sara Ford, Heather Jones, Catherine Higgins, Vanessa School of Computer Science University of Manchester Manchester United Kingdom Portland State University PortlandOR United States UK EQUATOR Centre Centre for Statistics in Medicine NDORMS University of Oxford Oxford United Kingdom College of Arts and Social Sciences Australian National University Canberra Australia Cancer Research UK Cambridge Centre University of Cambridge Cambridge United Kingdom Numerical Algorithms Group Oxford United Kingdom School of Computer Science University of St Andrews St Andrews United Kingdom Oxford e-Research Centre University of Oxford Oxford United Kingdom Electronics and Computer Science University of Southampton Southampton United Kingdom ELIXIR Hub Wellcome Genome Campus Cambridge United Kingdom EGI Foundation Amsterdam Netherlands School of Media and Communication University of Leeds Leeds United Kingdom Scientific Computing Department Science and Technology Facilities Council Rutherford Appleton Laboratory Didcot United Kingdom School of Social Sciences University of Manchester Manchester United Kingdom

Workshops are used to explore a specific topic, transfer knowledge, solve identified problems or create something new. In funded research projects and other research endeavours, workshops are the mechanism to gather the wider project, community or interested people together around a particular topic. However, natural questions arise: how do we measure the impact of these workshops? Do we know whether they are meeting the goals and objectives we set for them? What indicators should we use? In response to these questions, this paper will outline rules that will improve the measurement of the impact of workshops. Copyright © 2018, The Authors. All rights reserved.

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High-order Discretization of a Gyrokinetic Vlasov Model in Edge Plasma Geometry

arXiv

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arXiv 2017年

作者： Dorr, Milo R. Colella, Phillip Dorf, Mikhail A. Ghosh, Debojyoti Hittinger, Jeffrey A.F. Schwartz, Peter O. Center for Applied Scientific Computing Lawrence Livermore National Laboratory 7000 East Avenue L-561 LivermoreCA94550 United States Fusion Energy Program Lawrence Livermore National Laboratory 7000 East Avenue L-630 LivermoreCA94550 United States Applied Numerical Algorithms Group Lawrence Berkeley National Laboratory One Cyclotron Road Mail Stop 50A-1148 BerkeleyCA94720 United States

We present a high-order spatial discretization of a continuum gyrokinetic Vlasov model in axisymmetric tokamak edge plasma geometries. Such models describe the phase space advection of plasma species distribution functions in the absence of collisions. The gyrokinetic model is posed in a four-dimensional phase space, upon which a grid is imposed when discretized. To mitigate the computational cost associated with high-dimensional grids, we employ a high-order discretization to reduce the grid size needed to achieve a given level of accuracy relative to lower-order methods. Strong anisotropy induced by the magnetic field motivates the use of mapped coordinate grids aligned with magnetic flux surfaces. The natural partitioning of the edge geometry by the separatrix between the closed and open field line regions leads to the consideration of multiple mapped blocks, in what is known as a mapped multiblock (MMB) approach. We describe the specialization of a more general formalism that we have developed for the construction of high-order, finite-volume discretizations on MMB grids, yielding the accurate evaluation of the gyrokinetic Vlasov operator, the metric factors resulting from the MMB coordinate mappings, and the interaction of blocks at adjacent boundaries. Our conservative formulation of the gyrokinetic Vlasov model incorporates the fact that the phase space velocity has zero divergence, which must be preserved discretely to avoid truncation error accumulation. We describe an approach for the discrete evaluation of the gyrokinetic phase space velocity that preserves the divergence-free property to machine precision. A distinguishing feature of an edge geometry is the X point, where the poloidal field component vanishes. The inability to construct fully flux-surface aligned MMB coordinate systems that are smooth up to and through the X point requires the relaxation of alignment in the vicinity of this point. We therefore describe an approach for the generation of s

关键词： Finite volume method

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StarWatch 2.0: RFI Filter for SETI Signals

StarWatch 2.0: RFI Filter for SETI Signals

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International Conference on Cyberworlds

作者： Stanislav Klimenko Igor Nikitin Lialia Nikitina Kira Konich Kevin Reinartz Sergey Tyul'Bashev Institute of Computing for Physics and Technology Moscow Institute for Physics and Technology (State University) Protvino Russia Fraunhofer Institute for Algorithms and Scientific Computing Sankt Augustin Germany Bauhaus University Weimar Germany Fiziceskij institut imeni P N Lebedeva RAN Moskva Moskva RU

We extend our system for radio astronomical monitoring by a cross-validation filter, separating near Earth radio frequency interference (RFI) from deep space signals. The filter searches for similar signals in a nearby frequency band, coming from a different spatial direction than the tested signal. The filter passes the signals which do not have such duplicates. We apply this technique to a database of SETI Institute (***), containing 1.5 millions of sky observations in a frequency range 0.5-11.2 GHz, where our primary selection identified 28 strong signals possessing extraterrestrial (ET) signature. Crossvalidation allows to filter out 24 of those signals as satellite RFI. We present parameters for the remaining 4 signals and discuss statistical significance of these findings.

关键词： Satellites Satellite broadcasting Telescopes Brain models Antennas Radio astronomy

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Preconditioning for Efficiently Applying Algebraic Multigrid in Fully Implicit Reservoir Simulations

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SPE JOURNAL 2014年第4期19卷 726-736页

作者： Gries, Sebastian Stueben, Klaus Brown, Geoffrey L. Chen, Dingjun Collins, David A. Fraunhofer Institute for Algorithms and Scientific Computing Computer Modelling Group Limited

Fully implicit black-oil simulations result in huge, often very-ill-conditioned, linear systems of equations for different unknowns (e.g., pressure and saturations). It is well-known that the underlying Jacobian matrices contain both hyperbolic and nearly elliptic subsystems (corresponding to saturations and pressure, respectively). Because a reservoir simulation is typically driven by the behavior of the pressure, constrained-pressure-residual (CPR)-type two-stage preconditioning methods to solve the coupled linear systems are a natural choice and still belong to the most popular approaches. After a suitable extraction and decoupling, the computationally most costly step in such two-stage methods consists in solving the elliptic subsystems accurately enough. Algebraic multigrid (AMG) provides a technique to solve elliptic linear equations very efficiently. Hence, in recent years, corresponding CPR-AMG approaches have been extensively used in practice. Unfortunately, if applied in a straightforward manner, CPR-AMG does not always work as expected. In this paper, we discuss the reasons for the lack of robustness observed in practice, and present remedies. More precisely, we will propose a preconditioning strategy (based on a suitable combination of left and right preconditioning of the Jacobian matrix) that aims at a compromise between the solvability of the pressure subproblem by AMG and the needs of the outer CPR process. The robustness of this new preconditioning strategy will be demonstrated for several industrial test cases, some of which are very ill-conditioned. Furthermore, we will demonstrate that CPR-AMG can be interpreted in a natural way as a special AMG process applied directly to the coupled Jacobian systems.

关键词： preconditioning decoupling dynamic rowsumming Constrained Pressure residual Algebraic Multigrid

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Sparse grids and applications : Munich 2012 /

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2014年

作者： SGA2012 (Conference)

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StarWatch: Radio Astronomical Monitoring in Virtual Environment

StarWatch: Radio Astronomical Monitoring in Virtual Environm...

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International Conference on Cyberworlds

作者： Stanislav Klimenko Valery Malofeev Igor Nikitin Institute of Computing for Physics and Technology Protvino Russia Pushchino Radio Astronomy Observatory Pushchino Russia Fraunhofer Institute for Algorithms and Scientific Computing Sankt Augustin Germany

An application of Virtual Environment for real-time analysis of radio astronomical data is presented. Serving as an interface to radio astronomical databases or being applied to live data from the radio telescope, the application supports various data filters measuring signal-to-noise ratio (SNR), Doppler's drift, degree of signal localization on celestial sphere and other useful tools for signal extraction and classification. The application is created using Avango VE framework (***). The application has been used for analysis of radio astronomical data from SETI Institute (***).

关键词： Signal to noise ratio Extraterrestrial measurements Radon Virtual environments Electronic mail Databases Telescopes

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Radio Astronomical Monitoring in Virtual Environment

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Procedia Computer Science 2015年 66卷 592-601页

作者： Kira Konich Igor Nikitin Stanislav Klimenko Valery Malofeev Sergey Tyul’bashev Bauhaus University Weimar Germany Fraunhofer Institute for Algorithms and Scientific Computing Sankt Augustin Germany Institute of Computing for Physics and Technology Protvino Russia Pushchino Radio Astronomy Observatory Lebedev Physical Institute Pushchino Russia

We present StarWatch , our application for real-time analysis of radio astronomical data in Virtual Environment. Serving as an interface to radio astronomical databases or being applied to live data from the radio telescopes, the application supports various data filters measuring signal-to-noise ratio (SNR), Doppler's drift, degree of signal localization on celestial sphere and other useful tools for signal extraction and classification. Originally designed for the database of narrow band signals from SETI Institute (***), the application has been recently extended for the detection of wide band periodic signals, necessary for the search of pulsars. We will also address the detection of week signals possessing arbitrary waveforms and present several data filters suitable for this purpose.

关键词： scientific visualization virtual environments Big Data radio astronomy

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