检索结果-内蒙古大学图书馆

On the relevance of lift force modelling in turbulent wall flows with small inertial particles

学校读者我要写书评

暂无评论

arXiv 2024年

作者： Gao, Wei Shi, Pengyu Parsani, Matteo Costa, Pedro Mechanical Engineering Physical Science and Engineering Division King Abdullah University of Science and Technology Thuwal23955-6900 Saudi Arabia Applied Mathematics and Computational Science Computer Electrical and Mathematical Science and Engineering Division Extreme Computing Research Center King Abdullah University of Science and Technology Thuwal23955-6900 Saudi Arabia Université de Toulouse CNRS Toulouse France Helmholtz-Zentrum Dresden – Rossendorf Institute of Fluid Dynamics Dresden01328 Germany Process & Energy Department TU Delft Leeghwaterstraat 39 Delft2628 CB Netherlands

In particle-laden turbulent wall flows, lift forces can influence the near-wall turbulence. This has been recently observed in particle-resolved simulations, which, however, are too expensive to be used in upscaled models. Instead, point-particle simulations have been the method of choice to simulate the dynamics of these flows during the last decades. While this approach is simpler, cheaper, and physically sound for small inertial particles in turbulence, some issues remain. In the present work, we address challenges associated with lift force modelling in turbulent wall flows and the impact of lift forces in the near-wall flow. We performed direct numerical simulations (DNS) of small inertial point particles in turbulent channel flow for fixed Stokes number and mass loading while varying the particle size. Our results show that the particle dynamics in the buffer region, causing the apparent particle-to-fluid slip velocity to vanish, raises major challenges for accurately modelling lift forces. While our results confirm that lift forces have little influence on particle dynamics for sufficiently small particle sizes, for inner-scaled diameters of order one and beyond, lift forces become quite important near the wall. The different particle dynamics under lift forces results in the modulation of streamwise momentum transport in the near-wall region. We analyze this lift-induced turbulence modulation for different lift force models, and the results indicate that realistic models are critical for particle-modelled simulations to correctly predict turbulence modulation by particles in the near-wall region. © 2024, CC BY.

关键词： Wall flow

On the Theoretical Foundation of Overset Grid Methods for Hyperbolic Problems II: Entropy Bounded Formulations for Nonlinear Conservation Laws

学校读者我要写书评

暂无评论

SSRN

SSRN 2022年

作者： Nordström, Jan Kopriva, David A. Gassner, Gregor J. Department of Mathematics Florida State University TallahasseeFL32306 United States Computational Science Research Center San Diego State University San DiegoCA92182 United States Department for Mathematics and Computer Science Center for Data and Simulation Science University of Cologne Weyertal 86-90 Cologne50931 Germany Department of Mathematics Applied Mathematics Linköping University Linköping581 83 Sweden Department of Mathematics and Applied Mathematics University of Johannesburg P.O. Box 524 Auckland Park 2006 South Africa

We derive entropy conserving and entropy dissipative overlapping domain formulations for systems of nonlinear hyperbolic equations in conservation form, such as would be approximated by overset mesh methods. The entropy conserving formulation imposes two-way coupling at the artificial interface boundaries through nonlinear penalty functions that vanish when the solutions coincide. The penalty functions are expressed in terms of entropy conserving fluxes originally introduced for finite volume schemes. Entropy dissipation and additional coupling in the overlap region are added through the use of linear penalties. © 2022, The Authors. All rights reserved.

关键词： Entropy

Existence and regularity of inverse problem for the nonlinear fractional Rayleigh-Stokes equations

学校读者我要写书评

暂无评论

Existence and regularity of inverse problem for the nonlinea...

作者： Tran Bao, Ngoc Nguyen Hoang, Luc Vo Van, Au Nguyen, Huy Tuan Zhou, Yong Institute of Research Development Duy Tan University Da Nang550000 Viet Nam Department of Mathematics and Computer Science University of Science Ho Chi Minh City Viet Nam Vietnam National University Ho Chi Minh City Viet Nam Applied Analysis Research Group Faculty of Mathematics Statistics Ton Duc Thang University Ho Chi Minh City Viet Nam Faculty of Information Technology Macau University of Science Technology 999078 China Faculty of Mathematics Computational Science Xiangtan University Hunan411105 China

This paper investigates an inverse problem for fractional Rayleigh-Stokes equations with nonlinear source. The fractional derivative in time is taken in the sense of Riemann-Liouville. The proposed problem has many applications in some non-Newtonian fluids. We obtain some results on the existence and regularity of mild solutions. © 2020 John Wiley & Sons, Ltd.

关键词： Inverse problems

Deep Invertible Approximation of Topologically Rich Maps between Manifolds

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Puthawala, Michael Lassas, Matti Dokmanić, Ivan Pankka, Pekka de Hoop, Maarten V. Department of Mathematics and Statistics South Dakota State University Chicoine Hall Box 2225 BrookingsSD57007 United States Department of Mathematics and Statistics University of Helsinki HelsinkiFI-00014 Finland Department of Mathematics and Computer Science University of Basel Peterspl. 1 Basel4001 Switzerland Computational and Applied Mathematics and Earth Science Rice University HoustonTX77005 United States

How can we design neural networks that allow for stable universal approximation of maps between topologically interesting manifolds? The answer is with a coordinate projection. Neural networks based on topological data analysis (TDA) use tools such as persistent homology to learn topological signatures of data and stabilize training but may not be universal approximators or have stable inverses. Other architectures universally approximate data distributions on submanifolds but only when the latter are given by a single chart, making them unable to learn maps that change topology. By exploiting the topological parallels between locally bilipschitz maps, covering spaces, and local homeomorphisms, and by using universal approximation arguments from machine learning, we find that a novel network of the form T ◦ p ◦ E, where E is an injective network, p a fixed coordinate projection, and T a bijective network, is a universal approximator of local diffeomorphisms between compact smooth submanifolds embedded in n. We emphasize the case when the target map changes topology. Further, we find that by constraining the projection p, multivalued inversions of our networks can be computed without sacrificing universality. As an application, we show that learning a group invariant function with unknown group action naturally reduces to the question of learning local diffeomorphisms for finite groups. Our theory permits us to recover orbits of the group action. We also outline possible extensions of our architecture to address molecular imaging of molecules with symmetries. Finally, our analysis informs the choice of topologically expressive starting spaces in generative problems. © 2022, CC BY.

关键词： Topology

On the Theoretical Foundation of Overset Grid Methods for Hyperbolic Problems II: Entropy Bounded Formulations for Nonlinear Conservation Laws

学校读者我要写书评

暂无评论

arXiv 2022年

作者： Kopriva, David A. Gassner, Gregor J. Nordström, Jan Department of Mathematics Florida State University TallahasseeFL32306 United States Computational Science Research Center San Diego State University San DiegoCA92182 United States Department for Mathematics and Computer Science Center for Data and Simulation Science University of Cologne Weyertal 86-90 Cologne50931 Germany Department of Mathematics Applied Mathematics Linköping University Linköping581 83 Sweden Department of Mathematics and Applied Mathematics University of Johannesburg P.O. Box 524 Auckland Park2006 South Africa

We derive entropy conserving and entropy dissipative overlapping domain formulations for systems of nonlinear hyperbolic equations in conservation form, such as would be approximated by overset mesh methods. The entropy conserving formulation imposes a two-way coupling at the artificial interface boundaries through nonlinear penalty functions that vanish when the solutions coincide. The penalty functions are expressed in terms of entropy conserving fluxes originally introduced for finite volume schemes. In addition to the interface coupling, which is required, entropy dissipation and coupling can optionally be added through the use of linear penalties within the overlap *** Codes 65N85 Copyright © 2022, The Authors. All rights reserved.

关键词： Entropy

Superconductivity in ternary Mg4Pd7As6

学校读者我要写书评

暂无评论

arXiv 2024年

作者： Świątek, Hanna Gutowska, Sylwia Winiarski, Michal J. Wiendlocha, Bartlomiej Klimczuk, Tomasz Faculty of Applied Physics and Mathematics Gdańsk University of Technology Narutowicza 11/12 Gdansk80-233 Poland Advanced Materials Center Gdańsk University of Technology Narutowicza 11/12 Gdansk80-233 Poland University of Vienna Faculty of Physics Computational Materials Physics Kolingasse 14-16 Vienna1090 Austria AGH University of Krakow Faculty of Physics and Applied Computer Science al. Mickiewicza 30 Krakow30-059 Poland

We report the synthesis and characterization of a new compound Mg4Pd7As6, which was found to be a superconductor with Tc = 5.45 K. Powder X-ray diffraction confirms the U4Re7Si6 structure (space group Im-3m, no. 229) with the lattice parameter a = 8.2572(1) Å. Magnetization, specific heat, and electrical resistivity measurements indicate that it is a moderate-coupling (λ = 0.72) type-II superconductor. The electronic and phonon structures are calculated, highlighting the importance of antibonding Pd-As interactions in determining the properties of this material. The calculated electron-phonon copling parameter λ = 0.76 agrees very well with the experimental finding, which confirms the conventional pairing mechanism in Mg4Pd7As6. © 2024, CC BY.

关键词： Lattice constants

Adaptive numerical simulations with ***: A case study of Julia for scientific computing

学校读者我要写书评

暂无评论

arXiv 2021年

作者： Ranocha, Hendrik Schlottke-Lakemper, Michael Winters, Andrew R. Faulhaber, Erik Chan, Jesse Gassner, Gregor J. University of Münster Germany Department of Mathematics and Computer Science University of Cologne Germany Center for Data and Simulation Science University of Cologne Germany Department of Mathematics Applied Mathematics Linköping University Sweden Department of Computational and Applied Mathematics Rice University HoustonTX United States

We present ***, a Julia package for adaptive high-order numerical simulations of hyperbolic partial differential equations. Utilizing Julia's strengths, *** is extensible, easy to use, and fast. We describe the main design choices that enable these features and compare *** with a mature open source Fortran code that uses the same numerical methods. We conclude with an assessment of Julia for simulation-focused scientific computing, an area that is still dominated by traditional high-performance computing languages such as C, C++, and Fortran. Copyright © 2021, The Authors. All rights reserved.

关键词： Numerical models

QUADRATIC CONSTRAINT CONSISTENCY IN THE PROJECTION-FREE APPROXIMATION OF HARMONIC MAPS AND BENDING ISOMETRIES

学校读者我要写书评

暂无评论

arXiv 2023年

作者： Akrivis, Georgios Bartels, Sören Palus, Christian Department of Computer Science and Engineering University of Ioannina Ioannina451 10 Greece Institute of Applied and Computational Mathematics FORTH Heraklion Crete700 13 Greece Abteilung für Angewandte Mathematik Albert-Ludwigs-Universität Freiburg Hermann-Herder-Str. 10 Freiburgi. Br. 79104 Germany

We devise a projection-free iterative scheme for the approximation of harmonic maps that provides a second-order accuracy of the constraint violation and is unconditionally energy stable. A corresponding error estimate is valid under a mild but necessary discrete regularity condition. The method is based on the application of a BDF2 scheme and the considered problem serves as a model for partial differential equations with holonomic constraint. The performance of the method is illustrated via the computation of stationary harmonic maps and bending *** Codes 35J62 (35J50 35J57 65N30) Copyright © 2023, The Authors. All rights reserved.

关键词： Iterative methods

Bayesian Formulations for Graph Spectral Denoising

学校读者我要写书评

暂无评论

arXiv 2023年

作者： Leone, Sam Sun, Xingzhi Perlmutter, Michael Krishnaswamy, Smita Program for Applied Mathematics Yale University United States Department of Computer Science Yale University United States Department of Mathematics Boise State University United States Department of Genetics Yale School of Medicine United States Wu Tsai Institute Yale University United States FAIR Meta AI United States Computational Biology and Bioinformatics Program Yale University United States

Here we consider the problem of denoising features associated to complex data, modeled as signals on a graph, via a smoothness prior. This is motivated in part by settings such as single-cell RNA where the data is very high-dimensional, but its structure can be captured via an affinity graph. This allows us to utilize ideas from graph signal processing. In particular, we present algorithms for the cases where the signal is perturbed by Gaussian noise, dropout, and uniformly distributed noise. The signals are assumed to follow a prior distribution defined in the frequency domain which favors signals which are smooth across the edges of the graph. By pairing this prior distribution with our three models of noise generation, we propose Maximum A Posteriori (M.A.P.) estimates of the true signal in the presence of noisy data and provide algorithms for computing the M.A.P. Finally, we demonstrate the algorithms' ability to effectively restore signals from white noise on image data and from severe dropout in single-cell RNA sequence data. © 2023, CC BY.

关键词： Frequency domain analysis