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Data-driven spectral turbulence modeling for Rayleigh-Bénard convection

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arXiv 2023年

作者： Ephrati, Sagy R. Cifani, Paolo Geurts, Bernard J. Mathematics of Multiscale Modeling and Simulation Faculty EEMCS University of Twente Enschede7500 AE Netherlands Multiscale Energy Physics CCER Faculty Applied Physics Eindhoven University of Technology Eindhoven5600 MB Netherlands

A data-driven turbulence model for coarse-grained numerical simulations of two-dimensional Rayleigh-Bénard convection is proposed. The model starts from high-fidelity data and is based on adjusting the Fourier coefficients of the numerical solution, with the aim of accurately reproducing the kinetic energy spectra as seen in the high-fidelity reference findings. No assumptions about the underlying PDE or numerical discretization are used in the formulation of the model. We also develop a constraint on the heat flux to guarantee accurate Nusselt number estimates on coarse computational grids and high Rayleigh numbers. Model performance is assessed in coarse numerical simulations at Ra = 1010. We focus on key features including kinetic energy spectra, wall-normal flow statistics, and global flow statistics. The method of data-driven modeling of flow dynamics is found to reproduce the reference kinetic energy spectra well across all scales and yields good results for flow statistics and average heat transfer, leading to computationally cheap surrogate models. Large-scale forcing extracted from the high-fidelity simulation leads to accurate Nusselt number predictions across two decades of Rayleigh numbers, centered around the targeted reference at Ra = 1010MSC Codes 37M05, 37N10, 76F35, 76F55, 76F65 Copyright © 2023, The Authors. All rights reserved.

关键词： Heat flux

Analysis and Experimental Validation of a Pumped Two-Phase Loop for Multi-Component Cooling

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SSRN

SSRN 2023年

作者： Middelhuis, Myron Rojo, Miguel Muñoz Wits, Wessel Thermal and Fluid Engineering University of Twente Enschede7500 AE Netherlands Madrid Spain Mathematics of Multiscale Modeling and Simulation University of Twente Enschede7500 AE Netherlands

Miniaturization and enhanced performance of microchips have resulted in powerful electronic devices with high heat flux components. For these advanced electronic devices, the current heat transfer method of single-phase forced convection is reaching its thermal limit and more effective cooling solutions are needed. A pumped two-phase loop, in which a pump circulates a working fluid that evaporates to absorb heat, may offer a solution. In this paper, the cooling performance of a pumped two-phase loop is discussed and validated. A numerical tool has been developed to aid in designing a fit-for-purpose pumped two-phase loop and to predict its behaviour to changing system parameters and heat inputs. Results from the numerical model are compared with temperature, pressure and flow velocity measurements obtained from a prototype setup. Model predictions correspond well to the measured performances and findings regarding two-phase boiling behaviour are presented. The effects of applying varying heat loads on both a single evaporator and on multiple evaporators simultaneously either in series or in parallel have been investigated. The model is particularly useful for the rapid assessment of the layout of a pumped two-phase loop for high heat flux electronics cooling. © 2023, The Authors. All rights reserved.

关键词： Electronic cooling

Data-driven stochastic spectral modeling for coarsening of the two-dimensional Euler equations on the sphere

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arXiv 2023年

作者： Ephrati, Sagy R. Cifani, Paolo Viviani, Milo Geurts, Bernard J. Mathematics of Multiscale Modeling and Simulation Faculty EEMCS University of Twente Enschede7500 AE Netherlands Scuola Normale Superiore di Pisa Pisa Italy Multiscale Energy Physics CCER Faculty Applied Physics Eindhoven University of Technology Eindhoven5600 MB Netherlands

A resolution-independent data-driven stochastic parametrization method for subgrid-scale processes in coarsened fluid descriptions is proposed. The method enables the inclusion of high-fidelity data into the coarsened flow model, thereby enabling accurate simulations also with the coarser representation. The small-scale parametrization is introduced at the level of the Fourier coefficients of the coarsened numerical solution. It is designed to reproduce the kinetic energy spectra observed in high-fidelity data of the same system. The approach is based on a control feedback term reminiscent of continuous data assimilation. The method relies solely on the availability of high-fidelity data from a statistically steady state. No assumptions are made regarding the adopted discretization method or the selected coarser resolution. The performance of the method is assessed for the two-dimensional Euler equations on the sphere. Applying the method at two significantly coarser resolutions yields good results for the mean and variance of the Fourier coefficients. Stable and accurate large-scale dynamics can be simulated over long integration *** Codes 86-08, 76B99, 37M05 Copyright © 2023, The Authors. All rights reserved.

关键词： Stochastic systems

A continuous data assimilation closure for modeling statistically steady turbulence in large-eddy simulation

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arXiv 2023年

作者： Ephrati, Sagy R. Franken, Arnout Luesink, Erwin Cifani, Paolo Geurts, Bernard J. Department of Mathematical Sciences Chalmers University of Technology University of Gothenburg Gothenburg412 96 Sweden Mathematics of Multiscale Modeling and Simulation Faculty EEMCS University of Twente Enschede7500 AE Netherlands Multiscale Energy Physics CCER Faculty Applied Physics Eindhoven University of Technology Eindhoven5600 MB Netherlands

A closure model is presented for large-eddy simulation (LES) based on the three-dimensional variational data assimilation algorithm. The approach aims at reconstructing high-fidelity kinetic energy spectra in coarse numerical simulations by including feedback control to represent unresolved dynamics interactions in the flow as stochastic processes. The forcing uses statistics obtained from offline high-fidelity data and requires only few parameters compared to the number of degrees of freedom of LES. This modeling strategy is applied to geostrophic turbulence on the sphere and enables simulating indefinitely at reduced costs. It proves to accurately recover the energy spectra and the zonal velocity profiles in the coarse model, for three generic *** Codes 76F65, 76U60, 65P99 Copyright © 2023, The Authors. All rights reserved.

关键词： Large eddy simulation

Deconvolution of induced spatial discretization filters subgrid modeling in LES: application to two-dimensional turbulence 10

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Deconvolution of induced spatial discretization filters subg...

10th International Conference on Mathematical modeling in Physical Sciences, IC-MSQUARE 2021

作者： Boguslawski, A. Wawrzak, K. Paluszewska, A. Geurts, B.J. Czestochowa University of Technology al. Armii Krajowej 21 Czestochowa42-201 Poland Multiscale Modeling and Simulation Applied Mathematics University of Twente P.O. Box 217 Enschede7500 AE 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. © 2021 Institute of Physics Publishing. All rights reserved.

关键词： Large eddy simulation

Approximate Deconvolution Discretisation

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SSRN

SSRN 2023年

作者： Boguslawski, Andrzej Tyliszczak, Artur Geurts, B.J. Czestochowa University of Technology Poland Mathematics of Multiscale Modeling and Simulation Faculty EEMCS University of Twente PO Box 217 Enschede7500 AE Netherlands Multiscale Physics of Energy Systems Center for Computational Energy Research Faculty of Applied Physics Eindhoven University of Technology PO Box 513 Eindhoven5600 MB Netherlands

A new strategy is presented for the construction of high-order spatial discretisations extracted from a lower-order basic discretisation. The key consideration is that any discretisation of a derivative can be associated with exact differentiation of a `filtered' solution. By approximately inverting the numerically implied filter of the basic discretisation an augmented high-order method can be obtained. This construction is illustrated for finite difference (FD) discretisation schemes, solving partial differential equations in fluid mechanics. Knowing the implied filter of the basic discretisation, one can arrive at a corresponding much higher order method by (approximately) eliminating the implied spatial filter. We use deconvolution to compensate for the implied filter. This corresponds to a `sharpening' of numerical solution features before the application of the basic FD method. The combination will be referred to as Approximate Deconvolution Discretisation (ADD). The accuracy of the deconvolved FD scheme depends on the order of approximation of the inverse filter. We present the `sharpening' of several well-known FD operators for first- and second-order derivatives and quantify the achieved accuracy in terms of the modified wavenumber spectrum. Examples include high-order extensions up to new schemes with spectral accuracy. The practicality of the deconvolved FD schemes is illustrated by showing that ADD yields spectral accuracy for the Burgers equation and for double-jet flow of an incompressible fluid. © 2023, The Authors. All rights reserved.

关键词： Computational fluid dynamics

Hopping-Transport Mechanism for Reconfigurable Logic in Disordered Dopant Networks

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Physical Review Applied 2022年第6期17卷 064025-064025页

作者： Henri Tertilt Jesse Bakker Marlon Becker Bram de Wilde Indrek Klanberg Bernard J. Geurts Wilfred G. van der Wiel Andreas Heuer Peter A. Bobbert Institut für physikalische Chemie Westfälische Wilhelms-Universität Münster Münster Germany NanoElectronics Group University of Twente Enschede Netherlands Multiscale Modeling and Simulation Group Faculty of Electrical Engineering Mathematics and Computer Science MESA+ Institute for Nanotechnology and Center for Brain-Inspired Nano Systems (BRAINS) University of Twente Enschede Netherlands Center for Computational Energy Research (CCER) Eindhoven University of Technology Netherlands Fachbereich Physik Westfälische Wilhelms-Universität Münster Münster Germany Department of Applied Physics Eindhoven University of Technology Netherlands

We present an atomic-scale mechanism based on variable-range hopping of interacting charges enabling reconfigurable logic in dopant network processing units. Kinetic Monte Carlo simulations of the hopping process show temperature-dependent current-voltage characteristics and artificially evolved basic Boolean logic gates in very good agreement with experiment. The simulations provide unique insights into 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.

关键词： Doping effects Hopping transport Neuromorphic computing Devices for digital logic, storage & processing Disordered systems Doped semiconductors Genetic algorithm Monte Carlo methods

Computational modeling for high-fidelity coarsening of shallow water equations based on subgrid data

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arXiv 2021年

作者： Ephrati, Sagy R. Luesink, Erwin Wimmer, Golo Cifani, Paolo Geurts, Bernard J. Multiscale Modeling and Simulation Faculty EEMCS University of Twente P.O. Box 217 Enschede 7500 AE Netherlands Department of Mathematics Imperial College London United Kingdom Los Alamos National Laboratory New Mexico United States Gran Sasso Science Institute Viale F. Crispi L'Aquila7 67100 Italy Multiscale Energy Physics CCER Faculty Applied Physics Eindhoven University of Technology P.O. Box 213 Eindhoven5600 MB Netherlands

Small-scale features of shallow water flow obtained from direct numerical simulation (DNS) with two different computational codes for the shallow water equations are gathered offline and subsequently employed with the aim of constructing a reduced-order correction. This is used to facilitate high-fidelity online flow predictions at much reduced costs on coarse meshes. The resolved small-scale features at high resolution represent subgrid properties for the coarse representation. Measurements of the subgrid dynamics are obtained as the difference between the evolution of a coarse grid solution and the corresponding DNS result. The measurements are sensitive to the particular numerical methods used for the simulation on coarse computational grids and can be used to approximately correct the associated discretization errors. The subgrid features are decomposed into empirical orthogonal functions (EOFs), after which a corresponding correction term is constructed. By increasing the number of EOFs in the approximation of the measured values the correction term can in principle be made arbitrarily accurate. Both computational methods investigated here show a significant decrease in the simulation error already when applying the correction based on the dominant EOFs only. The error reduction accounts for the particular discretization errors that incur and are hence specific to the particular simulation method that is adopted. This improvement is also observed for very coarse grids which may be used for computational model reduction in geophysical and turbulent flow *** Codes 76B99, 65M22, 86-10 Copyright © 2021, The Authors. All rights reserved.

关键词： Finite volume method

Effects of Branching and Polydispersity on Thermal Conductivity of Paraffin Waxes

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SSRN

SSRN 2022年

作者： Boomstra, M.W. van Asseldonk, M.W.J. Geurts, B.J. Nazarychev, V.M. Lyulin, A.V. Soft Matter and Biological Physics Department of Applied Physics Eindhoven University of Technology P.O. Box 513 Eindhoven5600 MB Netherlands Center for Computational Energy Research P.O. Box 6336 Eindhoven5600 HH Netherlands Multiscale Modeling and Simulation Department of Applied Mathematics Faculty EEMCS University of Twente P.O. Box 217 Enschede 7500AE Netherlands Institute of Macromolecular Compounds Russian Academy of Sciences Bolshoi Prospect V.O. 31 St. Petersburg199004 Russia

Paraffin waxes are promising phase change materials, abundantly available at very low cost. Having large latent heat, these materials can be used for thermal energy storage. However, when used in heat batteries, paraffin’s low thermal conductivity prevents fast charging and discharging. This calls for the design of tailored hybrid materials with improved properties, the present study concentrates on properties of pure paraffin wax. Using fully atomistic molecular-dynamics (MD) simulations, we study the effects of polydispersity and branching on the thermal conductivity of paraffin waxes, in molten (450 K) and solid (250 K) state. Both branching and polydispersity affect the density and especially the crystallinity of the solid. Branching has a pronounced effect on crystallisation caused by inhibited alignment of the polymer backbones while the effect of polydispersity is less pronounced. The thermal conductivity (TC) has been simulated using the reverse non-equilibrium molecular-dynamics method, as well as the equilibrium Green-Kubo approach. Increased branching, added to backbones comprised of twenty monomers, results in decreasing TC of up to 30%, polydispersity only has an effect in the semi-crystalline state. Comparison to available experiments shows good agreement which validates the model details, applied force field and the calculation *** show that at comparable computational costs, the reverse non-equilibrium MD approach produces more reliable results for TC, as compared to the equilibrium Green-Kubo method. The major contribution to TC by acoustic phonon transport along the backbone was shown by analysing extreme cases. The phonon density of states (PDOS) of samples with high branching or with small chain length displayed diminished peaks in the acoustic range as compared to the PDOS of samples with low branching or larger chain length, respectively. The suggested MD approach can definitely be used to investigate specific material modifications aime

关键词： Phase change materials