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EFFECT OF PERIODIC ACCELERATIONS ON INTERFACE STABILITY IN A MULTILAYERED FLUID CONFIGURATION

AIAA JOURNAL 1991年第11期29卷 1894-1900页

作者： LYELL, MJ ROH, M West Virginia University Morgantown West Virginia 26505

The increasing number of research opportunities in a microgravity environment will benefit not only fundamental studies in fluid dynamics, but also technological applications such as those involving materials processing. In particular, fluid configurations that involve fluid-fluid interfaces would occur in a variety of experimental investigations. This work investigates the stability of a configuration involving fluid-fluid interfaces in the presence of a time-dependent (periodic) forcing. The fluid configuration is multilayered and infinite in extent. The analysis is linear and inviscid, and the acceleration vector is oriented perpendicular to each interface. A Floquet analysis is employed, and the resulting algebraic eigensystem is truncated. Nondimensional parameters appear in the algebraic system. A numerical study is performed to elucidate the regions of instability and the effect of parameter variation on the fluid configuration stability.

关键词： Microgravity Conservation of Mass Surface Tension Earth Space Processing Space Shuttle Stationkeeping Maneuvers numerical algorithms Fluid Mechanics Astronaut

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Latent hardening within the elasto-plastic self-consistent polycrystal homogenization to enable the prediction of anisotropy of AA6022-T4 sheets

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INTERNATIONAL JOURNAL OF PLASTICITY 2018年 105卷 141-163页

作者： Zecevic, Milovan Knezevic, Marko Univ New Hampshire Dept Mech Engn 33 Acad WayKingsbury Hall W119 Durham NH 03824 USA

Slip system hardening behavior of a given slip system is influenced more by shearing on another slip system known, as latent hardening, than by shearing on itself, known as self-hardening. This paper extends a recently developed dislocation-based hardening law within the elasto-plastic self-consistent polycrystal plasticity model to incorporate the latent hardening effects for predicting anisotropic response of polycrystalline face-centered cubic metals. In doing so, a new approach to overcome singularities associated with the self-consistent Eshelby solution procedure is proposed. The new approach is validated using a regularized Schmid law, where the singularity in Eshelby tensor calculation is intrinsically suppressed. Moreover, the solution procedure for single crystal stress increment is advanced to be based on a methodology involving the singular value decomposition to solve for shear increments. It is found that modeling crystallographic texture evolution and latent hardening successfully captures the anisotropic behavior of polycrystalline AA6022-T4 alloy. The model is subsequently successfully applied to predict large strain cyclic deformation of the same material. The implementation and insights from these predictions are presented and discussed in this paper.

关键词： Microstructures Crystal plasticity Polycrystalline material numerical algorithms AA6022-T4

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Rate-independent crystalline and polycrystalline plasticity, application to FCC materials

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INTERNATIONAL JOURNAL OF PLASTICITY 2000年第2期16卷 179-198页

作者： Knockaert, R Chastel, Y Massoni, E Ecole Mines Paris CEMEF F-06904 Sophia Antipolis France

This paper deals with the simulation of the mechanical response and texture evolution of cubic crystals and polycrystals for a rate-independent elastic-plastic constitutive law. No viscous effects are considered. An algorithm is introduced to treat the difficult case of multi-surface plasticity. This algorithm allows the computation of the mechanical response of a single crystal. The corresponding yield surface is made of the intersection of several hyper-planes in the stress space. The problem of the multiplicity of the slip systems is solved thanks to a pseudo-inversion method. Self and latent hardening are taken into account. In order to compute the response of a polycrystal, a Taylor homogenization scheme is used. The stress-strain response of single crystals and polycrystals is computed for various loading cases. The texture evolution predicted for compression, plane strain compression and simple shear are compared with the results given by a visco-plastic polycrystalline model. (C) 2000 Elsevier Science Ltd. All rights reserved.

关键词： crystal plasticity polycrystalline material elastic-plastic material numerical algorithms

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A crystal plasticity model incorporating the effects of precipitates in superalloys: Application to tensile, compressive, and cyclic deformation of Inconel 718

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INTERNATIONAL JOURNAL OF PLASTICITY 2017年 99卷 162-185页

作者： Ghorbanpour, Saeede Zecevic, Milovan Kumar, Anil Jahedi, Mohammad Bicknell, Jonathan Jorgensen, Luke Beyerlein, Irene J. Knezevic, Marko Univ New Hampshire Dept Mech Engn 33 Acad WayKingsbury HallW119 Durham NH 03824 USA Los Alamos Natl Lab Theoret Div Los Alamos NM 87545 USA Turbocam Int Turbocam Energy Solut Dover NH 03820 USA Univ Calif Santa Barbara Dept Mat Dept Mech Engn Santa Barbara CA 93106 USA

An elasto-plastic polycrystal plasticity model is developed and applied to an Inconel 718 (IN718) superalloy that was produced by additive manufacturing (AM). The model takes into account the contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. Non-Schmid effects and backstress are also included in the crystal plasticity model for activating slip. The hardening law for the critical resolved shear stress is based on the evolution of dislocation density. Using the same set of material and physical parameters, the model is compared against a suite of compression, tension, and large-strain cyclic mechanical test data applied in different AM build directions. It is demonstrated that the model is capable of predicting the particularities of both monotonic and cyclic deformation to large strains of the alloy, including decreasing hardening rate during monotonic loading, the non-linear unloading upon the load reversal, the Bauschinger effect, the hardening rate change during loading in the reverse direction as well as plastic anisotropy and the concomitant microstructure evolution. It is anticipated that the general model developed here can be applied to other multiphase alloys containing precipitates. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Microstructures Polycrystalline material Crystal plasticity numerical algorithms Inconel 718

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Advanced algorithms for studying the impact of climate changes on ozone levels in the atmosphere

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INTERNATIONAL JOURNAL OF ENVIRONMENT AND POLLUTION 2019年第1-3期66卷 212-238页

作者： Zlatev, Zahari Dimov, Ivan Farago, Istvan Georgiev, Krassimir Havasi, Agnes Aarhus Univ Dept Environm Sci Roskilde Denmark Bulgarian Acad Sci Inst Informat & Commun Technol Sofia Bulgaria MTA ELIE Numer Anal & Large Networks Res Grp H-1117 Budapest Hungary Budapest Univ Technol & Econ Dept Differential Equat Muegyet Rkp 3 H-1111 Budapest Hungary Eotvos Lorand Univ Dept Appl Anal & Computat Math Budapest Hungary

The impact of the increased temperature on some pollution levels is studied by developing climate scenarios and by running them on a period of 16 consecutive years. The mathematical model used in the experiments is a system of nonlinear partial differential equations (PDEs) and the space domain contains the whole of Europe together with some of its surroundings. Difficult computational problems arise after the direct discretisation of the spatial derivatives in the equations. The enormous computational problems can be treated successfully only by resolving five important tasks: 1) applying accurate and efficient numerical algorithms;2) selecting an appropriate splitting procedure;3) developing parallel codes;4) using high-speed computers;5) exploiting well the cache memories of the parallel computers. numerical results will be presented in order to illustrate both the efficiency of the code and the fact that the future climate changes will result in consistent increase of some pollution levels.

关键词： large-scale environmental models systems of nonlinear PDEs numerical algorithms splitting techniques parallel codes high-speed computers cache memory climate changes ozone levels damaging effects

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Building texture evolution networks for deformation processing of polycrystalline fcc metals using spectral approaches: Applications to process design for targeted performance

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INTERNATIONAL JOURNAL OF PLASTICITY 2010年第8期26卷 1183-1194页

作者： Shaffer, Joshua B. Knezevic, Marko Kalidindi, Surya R. Drexel Univ Dept Mat Sci & Engn Philadelphia PA 19104 USA Drexel Univ Dept Mech Engn & Mech Philadelphia PA 19104 USA Sci Forming Technol Corp Columbus OH 43235 USA

Microstructure sensitive design (MSD) has thus far focused mainly on the identification of the set of microstructures that are theoretically predicted to exhibit a designer-specified combination of elastic-plastic properties. In this paper, we present the extension of the MSD methodology to process design solutions. The goal of process design is to identify a processing route to transform a given initial microstructure into a different microstructure that exhibits superior property combinations by using an arbitrary sequence of available deformation processing options (hereafter referred to as hybrid processing routes). In this paper, we have focused on orientation distribution function (i.e. the 1-point statistics of crystallographic texture in the sample) as the descriptor of microstructure, and considered only the low temperature deformation processes. We have also restricted our attention to Taylor-type crystal plasticity models. With these idealizations, it is shown that it is possible to develop efficient algorithms in the MSD framework to build texture evolution networks that cover most of the texture hull. The advantages of this approach are expounded upon in this paper with selected case studies. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Microstructures Anisotropic material Crystal plasticity numerical algorithms Optimization

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Higher-order characteristics-based method for incompressible flow computation on unstructured grids

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AIAA JOURNAL 2001年第7期39卷 1280-1287页

作者： Zhao, Y Tai, CH Nanyang Technol Univ Sch Mech & Prod Engn Singapore 639798 Singapore

An algorithm for numerical simulation of incompressible hows on three-dimensional unstructured grids is presented. It is an upwind finite volume method based on the method of characteristics, which is made possible with the introduction of Chorin's artificial compressibility formulation (Chorin, A., "A numerical Method for Solving Incompressible Viscous Flow Problems," Journal of Computational Physics, Vol. 2, No. 1, 1967, pp. 12-26). Flow variables are calculated along characteristics, and their initial values are interpolated based on the signs of the corresponding characteristics. In addition, an upwind-biased interpolation method of third-order accuracy is used for interpolating flow variables on unstructured grids. With these inherent upwinding techniques for evaluating convection fluxes at control volume surfaces, no artificial viscosity is required. The discretized equations are solved by an explicit multistage Runge-Kutta time-stepping scheme, which is found to be efficient in terms of CPU and memory overheads. ii computer code has been developed using the numerical methods presented. A number of test cases, including two-dimensional/three-dimensional inviscid and viscous hows, have been calculated to validate the code and to evaluate the performance of the numerical algorithm. numerical results obtained are in good agreement with exact solutions and of her published experimental/numerical results. The convergence rate of numerical simulation is generally found to be satisfactory, The third-order characteristics-based scheme is found to be more accuarate than the second-order central scheme.

关键词： Unstructured Grid Incompressible Viscous Flow Courant Friedrichs Lewy Compressibility Freestream Conditions Streamlines Pattern Convection Tetrahedral Element numerical algorithms Continuity Equation

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QR factorization for the Cell Broadband Engine

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SCIENTIFIC PROGRAMMING 2009年第1-2期17卷 31-42页

作者： Kurzak, Jakub Dongarra, Jack Univ Tennessee Dept Elect Engn & Comp Sci Knoxville TN 37996 USA Oak Ridge Natl Lab Div Math & Comp Sci Oak Ridge TN USA Univ Manchester Sch Math Manchester Lancs England Univ Manchester Sch Comp Sci Manchester Lancs England

The QR factorization is one of the most important operations in dense linear algebra, offering a numerically stable method for solving linear systems of equations including overdetermined and underdetermined systems. Modern implementations of the QR factorization, such as the one in the LAPACK library, suffer from performance limitations due to the use of matrix-vector type operations in the phase of panel factorization. These limitations can be remedied by using the idea of updating of QR factorization, rendering an algorithm, which is much more scalable and much more suitable for implementation on a multi-core processor. It is demonstrated how the potential of the cell broadband engine can be utilized to the fullest by employing the new algorithmic approach and successfully exploiting the capabilities of the chip in terms of single instruction multiple data parallelism, instruction level parallelism and thread-level parallelism.

关键词： Cell broadband engine multi-core numerical algorithms linear algebra matrix factorization

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Wall distance search algorithm using voxelized marching spheres

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JOURNAL OF COMPUTATIONAL PHYSICS 2013年 241卷 76-94页

作者： Roget, Beatrice Sitaraman, Jayanarayanan Univ Wyoming Dept Mech Engn Laramie WY 82071 USA

Minimum distance to a solid wall is a commonly used parameter in turbulence closure formulations associated with the Reynolds Averaged form of the Navier Stokes Equations (RANS). This paper presents a new approach to efficiently compute the minimum distance between a set of points and a surface. The method is based on sphere voxelization, and uses fast integer arithmetic algorithms from the field of computer graphics. Using a simple test case where the number of points (N-p) and surface elements (N-b) can be independently specified, the present method is empirically estimated to be O((NpNb0.5)-N-0.8). An unstructured grid around an aircraft configuration (DLR-F6) is chosen as the test case for demonstration and validation. Multi-processor computations (up to 256 processors) are conducted to study efficiency and scalability. Encouraging results are obtained, with the sphere voxelization algorithm demonstrated to be more efficient than all of the alternate methods for computing minimum distances. However, a load imbalance does exist, which negatively impacts the scalability for large number of cores. A simple method for load re-balancing is formulated and tested, which results in significant improvements in both efficiency and scalability. (C) 2013 Elsevier Inc. All rights reserved.

关键词： numerical algorithms Computational fluid dynamics Turbulence modeling Computer graphics Minimum wall distance Voxel-based methods

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Boundary condition treatment in 2 x 2 systems of propagation equations

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INTERNATIONAL JOURNAL FOR numerical METHODS IN ENGINEERING 1998年第4期42卷 647-666页

作者： Guinot, V Lab Hydraul France F-38130 Echirolles France

numerical modelling of the water hammer phenomenon involves solving a 2 x 2 system of propagation equations numerically. In the present paper, this system is solved using the Piecewise Parabolic Method (PPM) Scheme, a higher-order extension of the Godunov Method. To reach high-order discretization accuracy, the PPM scheme uses six points in space to solve the advection equation. Hence, treatment of boundary conditions-which proves to be of importance to water hammer modelling-is not straightforward. Several options for the handling of boundary conditions are presented herein, and only one combination among nine is shown to provide good results. This shows that even very accurate numerical schemes may be of poor help in problem solving if boundary conditions are not handled properly. Results given by the PPM scheme are compared with those given by other solution techniques (Method Of Characteristics-MOC), proving the superior accuracy-efficiency relations used by the PPM over the usual approximations of the MOC. (C) 1998 John Wiley & Sons, Ltd.

关键词： numerical algorithms advection modelling finite volumes boundary conditions

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