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

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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High-Precision algorithms for Constructing Optimal Trajectories via Solving Hamiltonian Systems *

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IFAC Proceedings Volumes 2009年第2期42卷 70-75页

作者： Andrey A. Krasovskii Alexander M. Tarasyev Institute of Mathematics and Mechanics Ural Branch of RAS S. Kovalevskoi Str. 16 620219 Ekaterinburg Russia and Vienna Institute of Demography Austrian Academy of Sciences Wohllebengasse 12-14 1040 Vienna Austria Institute of Mathematics and Mechanics UrB RAS S. Kovalevskoi Str. 16 620219 Ekaterinburg Russia

The paper deals with analysis of optimal control problems arising in models of economic growth. The Pontryagin maximum principle is applied for analysis of the optimal investment problem. Specifically, the research is based on existence results and necessary conditions of optimality in problems with infinite horizon. Properties of Hamiltonian systems are examined for different regimes of optimal control. The existence and uniqueness result is proved for a steady state of the Hamiltonian system. Analysis of properties of eigenvalues and eigenvectors is completed for the linearized system in a neighborhood of the steady state. Description of behavior of the nonlinear Hamiltonian system is provided on the basis of results of the qualitative theory of differential equations. This analysis allows us to outline proportions of the main economic factors and trends of optimal growth in the model. A numerical algorithm for construction of optimal trajectories of economic growth is elaborated on the basis of constructions of backward procedures and conjugation of an approximation linear dynamics with the nonlinear Hamiltonian dynamics. High order precision estimates are obtained for the proposed algorithm. These estimates establish connection between precision parameters in the phase space and precision parameters for functional indices.

关键词： Nonlinear control systems numerical algorithms Precision measurements Economic design

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Comparison of numerical algorithms for bivariate sequential tests based on marginal criteria

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COMPUTATIONAL STATISTICS & DATA ANALYSIS 2005年第3期49卷 631-641页

作者： Zhao, YL Grambsch, PM Neaton, JD Univ Minnesota Sch Publ Hlth Div Biostat Minneapolis MN 55455 USA

Group sequential tests are widely used for interim analyses in randomized clinical trials. These tests have been extended to bivariate outcomes, but calculation of boundary values is computationally intensive. In this paper, we compare 3 algorithms: (1) quasi-Monte Carlo;(2) Schervish's MULNOR;and (3) a bivariate version of Armitage's recursive formula proposed by Jennison and Turnbull, for calculating boundary values for the L-region bivariate design which takes account of the correlation between the outcomes. Up to 5 interim analyses (stages) and a range of values for the correlation between the two endpoints were considered. The three algorithms produced very similar boundary values, but the quasi-Monte Carlo approach was much faster than the other two. The quasi-Monte Carlo method is an attractive approach for studying higher dimensions-designs with more stages and designs with more than two outcomes. The increased speed of this algorithm may permit the development of more flexible monitoring guidelines for multiple endpoints for clinical trials. (c) 2004 Elsevier B.V. All rights reserved.

关键词： group sequential monitoring bivariate responses numerical algorithms

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