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On electromagnetic forming processes in finitely strained solids: Theory and examples

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2009年第8期57卷 1391-1416页

作者： Thomas, J. D. Triantafyllidis, N. Univ Michigan Dept Aerosp Engn Ann Arbor MI 48109 USA

The process of electromagnetic forming (EMF) is a high velocity manufacturing technique that uses electromagnetic (Lorentz) body forces to shape sheet metal parts. EMF holds several advantages over conventional forming techniques: speed, repeatability, one-sided tooling, and most importantly considerable ductility increase in several metals. Current modeling techniques for EMF processes are not based on coupled variational principles to simultaneously account for electromagnetic and mechanical effects. Typically, separate solutions to the electromagnetic (Maxwell) and motion (Newton) equations are combined in staggered or lock-step methods, sequentially solving the mechanical and electromagnetic problems. The present work addresses these issues by introducing a fully Coupled Lagrangian (reference configuration) least-action variational principle, involving magnetic flux and electric potentials and the displacement field as independent variables. The corresponding Euler-Lagrange equations are Maxwell's and Newton's equations in the reference configuration, which are shown to coincide with their current configuration counterparts obtained independently by a direct approach. The general theory is subsequently simplified for EMF processes by considering the eddy Current approximation. Next, an application is presented for axisymmetric EMF problems. It is shown that the proposed variational principle forms the basis of a variational integration numerical scheme that provides an efficient staggered solution algorithm. As an illustration a number of such processes are simulated, inspired by recent experiments of freely expanding uncoated and polyurea-coated aluminum tubes. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： Electromechanical processes Finite strain Finite elements numerical algorithms Variational calculus

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A multilevel algorithm for solving the trust-region subproblem

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OPTIMIZATION METHODS & SOFTWARE 2009年第2期24卷 299-311页

作者： Toint, Philippe L. Tomanos, D. Weber-Mendonca, M. Univ Namur FUNDP Dept Math Namur Belgium

We present a multilevel numerical algorithm for the exact solution of the Euclidean trust-region subproblem. This particular subproblem typically arises when optimizing a nonlinear (possibly non-convex) objective function whose variables are discretized continuous functions, in which case the different levels of discretization provide a natural multilevel context. The trust-region problem is considered at the highest level (corresponding to the finest discretization), but information on the problem curvature at lower levels is exploited for improved efficiency. The algorithm is inspired by the method described in [J.J. More and D.C. Sorensen, On the use of directions of negative curvature in a modified Newton method, Math. Program. 16(1) (1979), pp. 1-20], for which two different multilevel variants will be analysed. Some preliminary numerical comparisons are also presented.

关键词： nonlinear optimization trust-region subproblem numerical algorithms multilevel methods

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Three-dimensional discrete element models for the granular statics and dynamics of powders in cavity filling

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2009年第1期57卷 10-31页

作者： Bierwisch, C. Kraft, T. Riedel, H. Moseler, M. Fraunhofer Inst Werkstoffmech IWM D-79108 Freiburg Germany

Rapid granular flow from a moving container and angle of repose formation were investigated by numerical simulations using the discrete element method (DEM) and experiments. Grain models of various geometrical complexity were studied and their ability to reproduce the experiments in those regimes was explored. The predictive power of the most realistic model for gravity driven cavity filling was assessed. Good agreement between computed and measured density distributions within the filled cavities provides a basis for numerical process variations aiming at homogenized density distributions. The effect of numerical coarse graining was found to be negligible for all properties of interest provided that force laws are scaled properly and corrections for boundary effects are taken into account. The proposed scaling was tested for a certain set of force laws but could be applied to different DEM forces as well. An analytic mass flow law for powder discharge from a moving container was derived and verified by our DEM simulations. (C) 2008 Elsevier Ltd. All rights reserved.

关键词： Dynamics Granular material Contact mechanics numerical algorithms Cavity filling

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Computational Procedures for Analysis of Two Schemes of Channel Assignment in Wireless Communication Networks

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AUTOMATIC CONTROL AND COMPUTER SCIENCES 2009年第2期43卷 96-103页

作者： Melikov, A. Z. Velibekov, A. M. Azerbaijan Natl Acad Sci Inst Cybernet 9F Agayev St AZ-1141 Baku Azerbaijan Azerbaijan Natl Acad Sci Inst Informat Technol AZ-1141 Baku Azerbaijan

propose numerical procedures for computing quality of service parameters in wireless cellular communication networks. We consider two schemes of isolated channel reservation for impatient handover calls. New calls can... 详细信息

关键词： wireless networks channel distribution quality of service parameters numerical algorithms

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The Nano-Jackhammer effect in probing near-surface mechanical properties

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INTERNATIONAL JOURNAL OF PLASTICITY 2009年第11期25卷 2045-2058页

作者： Cordill, M. J. Lund, M. S. Parker, J. Leighton, C. Nair, A. K. Farkas, D. Moody, N. R. Gerberich, W. W. Austrian Acad Sci Erich Schmid Inst Mat Sci A-8700 Leoben Austria Univ Minnesota Dept Chem & Mat Sci Minneapolis MN 55455 USA Virginia Tech Blacksburg VA 24061 USA Sandia Natl Labs Livermore CA 94550 USA

Because of its ease of implementation and insensitivity to indenter drift, dynamic indentation techniques have been frequently used to measure mechanical properties of bulk and thin film materials as a function of indenter displacement. However, the actual effect of the oscillating tip on the material response has not been examined. Recently, it has been shown that the oscillation used with dynamic indentation techniques alters the measured hardness value of ductile metallic materials, especially at depths less than 200 nm. The alteration in the hardness is due to the added energy associated with the oscillation which assists dislocation nucleation. Atomistic simulations on nickel thin films agree with experiments that more dislocations are nucleated during dynamic indents than with quasi-static indents. Through the analysis of quasi-static and dynamic indents made into nickel single crystals and thin films, a theory to describe this phenomenon is presented. This is coined the Nano-jackhammer effect, a combination of dislocation nucleation and strain rate sensitivity caused by indentation with a superimposed dynamic oscillation. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： Cyclic loading Mechanical testing Dislocations Dynamic fracture numerical algorithms

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Solving the Chemical Master Equation with the Aggregation-Disaggregation Method 18

Solving the Chemical Master Equation with the Aggregation-Di...

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IMACS World Congress/Modelling and Simulation Society-of-Australia-and-New-Zealand (MSSANZ)/18th MODSIM09 Biennial Conference on Modelling and Simulation

作者： Hegland, M. Australian Natl Univ CMA Inst Math Sci Canberra ACT 0200 Australia

ISBN: (纸本)9780975840078

Originally, aggregation and disaggregation were considered as acceleration techniques similar to multigrid methods for the solution of linear systems of equations. Recently we have demonstrated that these methods can also be used for the numerical solution of the chemical master equation. Here three scenarios are discussed where aggregation and disaggregation accelerate convergence, reduce complexity and lead to approximate solutions.

关键词： Chemical master equation aggregation / disaggregation numerical algorithms

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Anasazi Software for the numerical Solution of Large-Scale Eigenvalue Problems

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ACM TRANSACTIONS ON MATHEMATICAL SOFTWARE 2009年第3期36卷 13:1-13:23页

作者： Baker, C. G. Hetmaniuk, U. L. Lehoucq, R. B. Thornquist, H. K. Sandia Natl Labs Livermore CA 94550 USA

Anasazi is a package within the Trilinos software project that provides a framework for the iterative, numerical solution of large-scale eigenvalue problems. Anasazi is written in ANSI C++ and exploits modern software paradigms to enable the research and development of eigensolver algorithms. Furthermore, Anasazi provides implementations for some of the most recent eigensolver methods. The purpose of our article is to describe the design and development of the Anasazi framework. A performance comparison of Anasazi and the popular FORTRAN 77 code ARPACK is given.

关键词： algorithms Design Performance Reliability Theory Eigenvalue problems numerical algorithms generic programming object-oriented programming large-scale scientific computing

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Mathematical modelling of particle-fluid flows in microchannels

Mathematical modelling of particle-fluid flows in microchann...

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作者： Chayantrakom, Kittisak Curtin University of Technology

学位级别：master

Flows of fluids and solid particles through microchannels have a very wide range of applications in biological and medical science and engineering. Understanding the mechanism of microflows will help to improve the development of the devices and systems in those applications. The aim of this study is to develop a sophisticated simulation and analysis technique for the study of fluid-particle flow through microchannels. This work involves construction of mathematical models, development of analytical methods and numerical algorithms, and numerical investigation and analysis.%%%%The study consists of three parts. The first part of the research focuses on the transient flow of an incompressible Newtonian fluid through a micro-annual with a slip boundary. The flow of the fluid is governed by the continuity equation and the Navier-Stokes equations, and is driven by the pressure field with a timevarying pressure gradient. By using the Fourier series expansion in time and Bessel functions in space, an exact solution is derived for the velocity field. The velocity solution is then used to obtain the exact solutions for the flow rate and the stress field. Based on the exact solutions, the influence of the slip parameter on the flow behaviour is then investigated.%%%%The second part of the research focuses on the particle-fluid flow in microchannels. The transport of fluid in the vessel is governed by the continuity equation and the transient Navier-Stokes equations, while the motion of the particles is governed by Newton’s laws. The particle-wall and particle-particle interactions are modelled by the interacting forces, while the particle-fluid interaction is described by the fluid drag force. A numerical scheme based on the finite element method and the Arbitary Lagrangian-Eulerian method is developed to simulate the motion of the particles and the fluid flow in the vessels. The influence of boundary slip on the velocity field in the fluid is also investigated numerically.%

关键词： flows fluids solid particles microchannels biological science medical science engineering microflows mathematical models analytical methods numerical algorithms numerical investigation

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Enhancement of the finite-element method for the analysis of vertical train-track interactions

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART F-JOURNAL OF RAIL AND RAPID TRANSIT 2009年第6期223卷 609-620页

作者： Yang, S. C. Korea Railroad Res Inst Vehicle & Track Res Dept Uiwang Si 437757 Gyeonggi Do South Korea

The accuracy of the simulation of train-track interaction can be improved by adding a node at the point of loading, when a contact force exists within the beam element that models the rail. This causes difficulties in the formulation and entails large computational times since the node moves along with the point of contact. In this study, a more simplified method that can represent the discontinuities of slope deflection at the location of both the sleeper and of the moving contact force, while employing the customary finite-element method, has been presented. The simulation of the existence of such an added node without explicitly including it is realized by modifying the Hertzian spring coefficient and adding the additional mass matrix to the existing mass matrix. Also, to enhance the convergence and to overcome the computational burden of load vector calculations at all iterations, a modified Newmark-beta integral scheme is proposed. The suggested model was validated by comparing the results with field-test data and other numerical models reported in the literature by other researchers.

关键词： train-track interaction finite-element Timoshenko beam discontinuity in slope deflection numerical algorithms wheel flat

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Kalman—Type Filtering for Stochastic Systems with State—Dependent Noise and Markovian Jumps

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IFAC Proceedings Volumes 2009年第10期42卷 1375-1380页

作者： A.–M. Stoica V. Dragan I. Yaesh Faculty of Aerospace Engineering University “Politehnica” of Bucharest Bucharest Romania Institute of Mathematics of the Romanian Academy Bucharest Romania IMI Advanced Systems Div. Ramat-Hasharon Israel

The paper presents a Kalman–type filtering problem for linear stochastic systems subjected both to state–dependent white noise and to Markovian jumps. The results are derived using a unified approach for the continuous–time case and for the discrete-time models of the plant. It is proved that the optimal filters gains depend on the solutions of some specific Riccati-type systems which generalize the well–known equations from the classical Kalman filtering.

关键词： Kalman filters Stochastic systems Markov parameters Riccati equations numerical algorithms

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