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4th International Conference on Supercomputer Technologies of Mathematical Modelling, SCTeMM 2019

作者： Sivtsev, Petr V. Kolesov, Aleksandr E. Zakharov, Petr E. Yang, Ying Research Laboratory multiscale Matheatical Modeling and Computing Ammosov North-Eastern Federal University Belinskogo 58 Yakutsk677000 Russia Hunan Key Laboratory for Computation and Simulation in Science and Engineering School of Mathematics and Computational Science Xiangtan University Xiangtan Hunan411105 China

Numerical simulation of the stress-strain state of a composite material may be difficult due to large computational complexity associated with a grid resolution of a large number of inclusions. To overcome the problem one may use the homogenization method. But for material with plastic properties, proper modeling of yield stress and hardening may be overcomplicated. In this work we use some simplification associated with a small proportion of inclusions and restriction of stress values by matrix material strength. As model problem, we use deformation of concrete deep beam reinforced with steel or basalt fiber inclusions. For the numerical solution, the finite element method was applied using the FEniCS computing platform. © Published under licence by IOP Publishing Ltd.

关键词： Homogenization method

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Deconvolution of induced spatial discretization filters subgrid modeling in LES: application to two-dimensional turbulence

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Journal of Physics: Conference Series 2021年第1期2090卷

作者： A Boguslawski K Wawrzak A Paluszewska B J Geurts Czestochowa University of Technology al. Armii Krajowej 21 42-201 Czestochowa Poland Multiscale Modeling and Simulation Applied Mathematics University of Twente P.O. Box 217 7500 AE Enschede Netherlands

The paper presents a new approximate deconvolution subgrid model for Large Eddy simulation in which corrections to implicit filtering due to spatial discretization are integrated explicitly. The top-hat filter implied by second-order central finite differencing is a key example, which is discretised using the discrete Fourier transform involving all the mesh points in the computational domain. This discrete filter kernel is inverted by inverse Wiener filtering. The inverse filter obtained in this way is used to deconvolve the resolved scales of the implicitly filtered velocity field on the computational grid. Subgrid stresses are subsequently calculated directly from the deconvolved velocity field. The model was applied to study decaying two-dimensional turbulence. Results were compared with predictions based on the Smagorinsky model and the dynamic Germano model. A posteriori testing in which Large Eddy simulation is compared with filtered Direct Numerical simulation obtained with a Fourier spectral method is included. The new model presented strictly speaking applies to periodic problems. The idea of recovering a high-order inversion of the numerically induced filter kernel can be extended to more general non-periodic problems, also in three spatial dimensions.

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Mechanism for reconfigurable logic in disordered dopant networks

Research Square

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Research Square 2021年

作者： Tertilt, Henri Bakker, Jesse Becker, Marlon de Wilde, Bram Klanberg, Indrek Geurts, Bernard J. van der Wiel, Wilfred G. Heuer, Andreas Bobbert, Peter A. Institut für physikalische Chemie Westfälische Wilhelms-Universität Münster Münster Germany University of Twente Enschede Netherlands Multiscale Modeling and Simulation Group Faculty of Electrical Engineering Mathematics and Computer Science Center for Brain-Inspired Nano Systems University of Twente Enschede Netherlands Eindhoven University of Technology Eindhoven5600 MB Netherlands Fachbereich Physik Westfälische Wilhelms-Universität Münster Münster Germany Molecular Materials and Nanosystems Group Center for Computational Energy Research Eindhoven University of Technology Eindhoven Netherlands

We present an atomic-scale mechanism based on variable-range hopping of interacting charges enabling reconfigurable logic and nonlinear classification tasks in dopant network processing units in silicon. Kinetic Monte Carlo simulations of the hopping process show temperature-dependent current-voltage characteristics, artificial evolution of basic Boolean logic gates, and fitness-dependent gate abundances in striking agreement with experiment. The simulations provide unique insights in the local electrostatic potential and current flow in the dopant network, showing subtle changes induced by control voltages that set the conditions for the logic operation. These insights will be crucial in the systematic further development of this burgeoning technology for unconventional computing. The establishment of the principles underlying the logic functionality of these devices encourages the exploration and utilization of the same principles in other materials and device geometries. © 2021, CC BY.

关键词： Monte Carlo methods

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Numerical homogenization of elastoplastic deformations of composite material with small proportion of inclusions

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Journal of Physics: Conference Series 2019年第1期1392卷

作者： Petr V. Sivtsev Aleksandr E. Kolesov Petr E. Zakharov Ying Yang Research Laboratory 'Multiscale Matheatical Modeling and Computing' Ammosov North-Eastern Federal University 58 Belinskogo 677000 Yakutsk Russia Hunan Key Laboratory for Computation and Simulation in Science and Engineering School of Mathematics and Computational Science Xiangtan University Xiangtan 411105 Hunan China

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Comparison of computational codes for direct numerical simulations of turbulent Rayleigh-Bénard convection

arXiv

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arXiv 2018年

作者： Kooij, Gijs L. Botchev, Mikhail A. Frederix, Edo M.A. Geurts, Bernard J. Horn, Susanne Lohse, Detlef Van Der Poel, Erwin P. Shishkina, Olga Stevens, Richard J.A.M. Verzicco, Roberto Multiscale Modeling and Simulation Faculty EEMCS University of Twente Enschede Netherlands Applied Mathematics and Mathematical Physics Imperial College London Physics of Fluids Faculty of Science and Technology University of Twente Enschede Netherlands Mathematics of Computational Science Faculty EEMCS University of Twente Enschede Netherlands Keldysh Institute of Applied Mathematics Russian Academy of Sciences Moscow Russia Max Planck Institute for Dynamics and Self-Organization Göttingen Germany Dipartimento di Ingegneria Meccanica Università di Roma Tor Vergata Rome Italy Faculty of Applied Physics Fluid Dynamics Laboratory Eindhoven University of Technology Eindhoven Netherlands Earth Planetary and Space Sciences University of California Los Angeles United States

Computational codes for direct numerical simulations of Rayleigh-Bénard (RB) convection are compared in terms of computational cost and quality of the solution. As a benchmark case, RB convection at Ra = 108and Pr = 1 in a periodic domain, in cubic and cylindrical containers is considered. A dedicated second-order finite-difference code (AFID/RBflow) and a specialized fourth-order finite-volume code (Goldfish) are compared with a general purpose finite-volume approach (OpenFOAM) and a general purpose spectral-element code (Nek5000). Reassuringly, all codes provide predictions of the average heat transfer that converge to the same values. The computational costs, however, are found to differ considerably. The specialized codes AFID/RBflow and Goldfish are found to excel in efficiency, outperforming the general purpose flow solvers Nek5000 and OpenFOAM by an order of magnitude with an error on the Nusselt number Nu below 5%. However, we find that Nu alone is not sufficient to assess the quality of the numerical results: in fact, instantaneous snapshots of the temperature field from a near wall region obtained for deliberately under-resolved simulations using Nek5000 clearly indicate inadequate flow resolution even when Nu is converged. Overall, dedicated special purpose codes for RB convection are found to be more efficient than general purpose codes. Copyright © 2018, The Authors. All rights reserved.

关键词： Direct numerical simulation

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Free-surface flow simulations for moored and floating offshore platforms 7

Free-surface flow simulations for moored and floating offsho...

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7th European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS Congress 2016

作者： Veldman, Arthur E.P. Luppes, Roel Van Der Plas, Peter Van Der Heiden, Henri Düz, Bülent Seubers, Henk Helder, Joop Bunnik, Tim Huijsmans, René Institute for Mathematics and Computer Science University of Groningen Groningen Netherlands Department of Ship Hydrodynamis Delft University of Technology Delft Netherlands Maritime Reseach Institute MARIN Wageningen Netherlands Multiscale Modeling and Simulation University of Twente Enschede Netherlands

ISBN: (纸本)9786188284401

During the development of the ComFLOW simulation method many challenges have to be tackled concerning the flow modelling and the numerical solution algorithm. Examples here of are wave propagation, absorbing boundary conditions, fluid-solid body interaction, turbulence modeling and numerical efficiency. Some of these challenges will be discussed in the paper, in particular the design of absorbing boundary conditions and the numerical coupling for fluid-solid body interaction. As a demonstration of the progress made, a number of simulation results for engineering applications from the offshore industry will be presented: a wave-making oscillating buoy, a free-fall life boat dropping into wavy water, and wave impact against a semi-submersible offshore platform. For those applications, MARIN has carried out several validation experiments.

关键词： Computational fluid dynamics

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DNS and les of excited rectangular jets 8

DNS and les of excited rectangular jets

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8th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2013

作者： Tyliszczak, Artur Geurts, Bernard J. Department of Mechanical Engineering and Computer Science Institute of Thermal Machinery Czestochowa University of Technology Al. Armii Krajowej 21 Czestochowa42-200 Poland Department of Applied Mathematics Multiscale Modeling and Simulation University of Twente P.O. Box 217 AE Enschede7500 Netherlands

The paper presents results of numerical studies devoted to an active flow control method applied to jet flow and focusses on rectangular jets with aspect ratio Ar = 1, 2 and 3. Square and rectangular jets are more unstable than their circular counterparts, which is expressed by an increased intensity of mixing. It is shown that the application of a suitable excitation (forcing) at the jet nozzle can qualitatively alter the character of the flow, resulting in an increased spreading rate of passive tracer. The excitation is obtained from a superposition of axial and helical forcing terms. We study the mixing in the flow upon varying parameters such as the frequency of the excitations and possible phase shifts between components. The numerical results are obtained applying LES and DNS based on a high-order compact difference code for the incompressible flows.

关键词： Aspect ratio

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Pulsatile flow in model cerebral aneurysms

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Procedia Computer Science 2011年 4卷 811-820页

作者： Julia Mikhal Bernard J. Geurts Multiscale Modeling and Simulation Department of Applied Mathematics University of Twente P.O. Box 217 7500 AE Enschede The Netherlands Anisotropic Turbulence Department of Applied Physics Eindhoven University of Technology P.O. Box 513 5600 MB Eindhoven The Netherlands

We present an immersed boundary method based on volume penalization, with which pulsatile flow in a model cerebral aneurysm is simulated. The model aneurysm consists of a curved vessel merged with a spherical cavity. The dominant vortical structures arising in the time-dependent flow are discussed and the evolution of the maximal shear stress in the aneurysm is analyzed. We approximate flow properties of blood by those of an incompressible Newtonian fluid. The flow inside the aneurysm is simulated with the use of a skew-symmetric finite-volume discretization and explicit time-stepping. We focus on effects due to variations in the amplitude of the pulsatile flow as well as due to changes in the Reynolds number (Re) by studying flow at Re = 100, 250 and 500. At Re = 500 a complex timedependence in the shear stress levels is observed, reflecting the lively development of the flow in the model aneurysm in which vortices are created continuously inside the curved vessel and in the spherical cavity of the aneurysm. An increase in the amplitude of the pulsatile flow increases the shear stress levels somewhat, but at Re = 500 the flow is mainly dominated by its intrinsic unsteadiness. Reducing the Reynolds number yields a stronger contribution of the periodic pulsatile flow forcing: at Re = 100 we find a strong dominance of shear stress levels due to the forcing, while at Re = 250 the intrinsic and pulsatile unsteadiness are of comparable importance.

关键词： cerebral aneurysm pulsatile flow immersed boundary method volume-penalization incompressible flow shear stress

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Intermittency effects in rotating decaying turbulence 6

Intermittency effects in rotating decaying turbulence

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6th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2009

作者： Kuczaj, Arkadiusz K. Geurts, Bernard J. Holm, Darryl D. P.O. Box 25 Petten1755 ZG Netherlands Multiscale Modeling and Simulation NACM J.M. Burgers Center University of Twente P.O. Box 217 Enschede7500 AE Netherlands Fluid Dynamics Laboratory Department of Applied Physics Eindhoven University of Technology P.O. Box 513 Eindhoven5300 MB Netherlands Mathematics Department Imperial College London LondonSW7 2AZ United Kingdom CCS2 Los Alamos National Laboratory Los AlamosNM87545 United States

Rotation modulates turbulence causing columnar structuring of a turbulent flow in case of sufficiently strong rotation. This yields significant changes in the flow characteristics and dispersion properties, which makes rotational turbulence modulation particularly relevant in the context of atmospheric and oceanic flows. Here we investigate the canonical flow of turbulence in a periodic box, subjected to rotation about a fixed vertical axis. As point of reference we consider direct numerical simulations of homogeneous isotropic turbulence. Modulation due to rotation at various rotation rates (i.e., different Rossby numbers) is investigated. Special attention is paid to the alteration of intermittency, which is measured in terms of changes in the scaling of the structure functions. A reduction of intermittency quantified with the longitudinal structure functions in the direction perpendicular to the rotation axes will be presented. These numerical findings correspond well to recent results obtained in experiments by Seiwert et al. (2008) [1]. © 2009 TSFP4 Symposium. All Rights Reserved.

关键词： Rotation

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Direct and Large-Eddy simulation VI 1

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丛书名： ERCOFTAC Series

1000年

作者： Eric Lamballais Rainer Friedrich Bernard J. Geurts Olivier Métais

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