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numerical analysis and elastic-plastic deformation behavior of anisotropically damaged solids

INTERNATIONAL JOURNAL OF PLASTICITY 2002年第9期18卷 1237-1270页

作者： Brünig, M Univ Dortmund Lehrstuhl Baumech Stat D-44221 Dortmund Germany

The present paper is concerned with the numerical modelling of the large elastic plastic deformation behavior and localization prediction of ductile metals which are sensitive to hydrostatic stress and anisotropically damaged. The model is based on a generalized macroscopic theory within the framework of nonlinear continuum damage mechanics. The formulation relies on a multiplicative decomposition of the metric transformation tensor into elastic and damaged-plastic parts. Furthermore, undamaged configurations are introduced which are related to the damaged configurations via associated metric transformations which allow for the interpretation as damage tensors. Strain rates are shown to be additively decomposed into elastic, plastic and damage strain rate tensors. Moreover, based on the standard dissipative material approach the constitutive framework is completed by different stress tensors, a yield criterion and a separate damage condition as well as corresponding potential functions. The evolution laws for plastic and damage strain rates are discussed in some detail. Estimates of the stress and strain histories are obtained via an explicit integration procedure which employs an inelastic (damage-plastic) predictor followed by an elastic corrector step. numerical simulations of the elastic-plastic deformation behavior of damaged solids demonstrate the efficiency of the formulation. A variety of large strain elastic-plastic-damage problems including severe localization is presented, and the influence of different model parameters on the deformation and localization prediction of ductile metals is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： damage elastic plastic material finite strain finite element numerical algorithms

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Matchsticks, scramjets, and black holes: numerical simulation faces reality

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AIAA JOURNAL 2002年第8期40卷 1481-1494页

作者： Oran, ES USN Res Lab Lab Computat Phys & Fluid Dynam Washington DC 20375 USA

The evolution of the science and art of numerical simulation of complex, complicated fluid flows has made enormous strides in the past 40 years. We have progressed from relatively simplified one-dimensional steady-state results to fully three-dimensional, time-dependent simulations including very complex physics. These advances have been driven by new computational hardware, new algorithms for solving the equations, and the real need for this technology. The broad range of applications that are possible are emphasized and some of what we can now do, what we have learned, and where we might go with this exciting technology in the future is described.

关键词： numerical Simulation Scramjet Conservation Equations Detonation High Performance Computing Vortices Torpedoes Electromagnetic Radiation MHD numerical algorithms

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Experimental and numerical investigation of the Bridgman growth of a transparent material

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2002年第3期16卷 324-335页

作者： Simpson, JE Garimella, SV de Groh, HC Purdue Univ Sch Mech Engn W Lafayette IN 47907 USA NASA John H Glenn Res Ctr Micrograv Sci Div Cleveland OH 44135 USA

A combined experimental and numerical study of the horizontal Bridgman growth of pure succinonitrile has been performed. The effect of convection on interface propagation and shape is quantified and discussed. Measurements were obtained both under conditions of no-growth and for a 40-mum/s growth rate. The quantities measured include interface shape and location, melt velocities, and temperature boundary conditions on the ampoule exterior. The melt velocities were measured using a new technique that employed digital cameras to image the locations of seed particles in the melt. The growth front was stable and nondendritic but was significantly distorted by the influence of convection in the melt and, for the growth case, by the moving temperature boundary conditions along the ampoule. Both two- and three-dimensional numerical simulations of the growth process were performed. Temperatures throughout the phase-change material and ampoule, as well as melt velocities, were obtained from the simulations. The predicted interface shapes and melt velocities agree well with experimental results. Two different numerical algorithms were used;the utility of each for simulating phase-change problems is discussed. This combined experimental and numerical study provides a database for the validation of phase-change numerical models, in addition to furnishing detailed information about the influence of convection on the Bridgman growth process. In ongoing work, the computer models presented are being used to simulate alloy solidification problems.

关键词： Natural Convection numerical Stability numerical Simulation Phase Change Materials numerical algorithms Thermocouples Flow Visualization Thermal Boundary Condition Isotherms Transient Conduction

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Robust fault detection for uncertain discrete-time systems

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2002年第2期25卷 291-301页

作者： Wang, HB Lam, J Univ Hong Kong Hong Kong Hong Kong Peoples R China

The fault detection problem under structured uncertainties in the system matrices is considered. The sensitivity of robust fault detection is one of the important issues considered in the fault detection and isolation development. To enhance this characteristic, an unconstrained optimization approach is taken to design a robust fault detection observer. The approach aims at enhancing the fault detection robustness to uncertainties without sacrificing the fault detection sensitivity, which was seldom addressed before. Furthermore, other objectives related to the observer gain and the eigenstructure conditioning of the observer system are also taken into account. The gradient-based optimization approach is facilitated by the explicit gradient expressions derived. numerical simulation has also demonstrated the tradeoffs between different objectives as well as the effectiveness of the present methodology.

关键词： Fault Detection numerical Simulation Observability Gramian MATLAB Vertical Takeoff and Landing Mathematical Models Collective Pitch Control numerical algorithms Aerospace System

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Compensating for order variation in mesh refinement for direct transcription methods II: Computational experience

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JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS 2002年第2期143卷 237-261页

作者： Betts, JT Biehn, N Campbell, SL Huffman, WP N Carolina State Univ Coll Phys & Math Sci Dept Math Raleigh NC 27695 USA Boeing Co Math & Engn Anal Seattle WA 98124 USA N Carolina State Univ Operat Res Program Raleigh NC 27695 USA

The numerical theory for Implicit Runge Kutta methods shows that there can be order reduction when these methods are applied to either stiff or differential algebraic equations. A previous paper introduced a way to try and compensate for this order reduction in designing mesh refinement strategies. This paper presents the results from a number of computational studies on the effectiveness of this approach. In addition, we present a new test problem which can be used to examine the efficiency of codes developed for a particular class of applications. (C) 2002 Elsevier Science B.V. All rights reserved.

关键词： optimal control mesh refinement numerical algorithms

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Limit-cycle oscillation induced by nonlinear aerodynamic forces

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AIAA JOURNAL 2002年第11期40卷 2197-2205页

作者： Dotson, KW Baker, RL Sako, BH Aerosp Corp Struct Dynam Dept Los Angeles CA 90009 USA Aerosp Corp Fluid Mech Dept Los Angeles CA 90009 USA

The aerodynamic How state on launch vehicle payload fairings and aircraft wings can change abruptly during transonic flight if the angle of attack reaches a critical value. The nonlinear pressure variation associated with a flow-state change induces transient structural responses that may converge to a limit-cycle oscillation (LCO). In this steady state, the work conducted during the flow-state changes balances the energy dissipation from structural damping. Analysis of this transonic LCO, phenomenon is often conducted using a semi-empirical, unsteady pressure variation in which the levels for the flow states are determined from steady wind-tunnel test data. The presented theory addresses the condition in which the flow-state changes occur near a quasi-steady, nonzero angle of attack. The analysis for the resulting asymmetric forcing function complements the authors' existing derivations for a symmetric forcing function at zero angle of attack. Both the asymmetric and the symmetric analyses develop closed-form equations for the structural response frequency and amplitude. These expressions show that the solution space contains a subcritical Hopf bifurcation when the critical angle of attack equals the quasi-steady angle of attack. They also show that a saddle-node bifurcation, or fold, corresponds to the critical angle of attack beyond which LCO will not occur for a given quasi-steady angle of attack.

关键词： Aerodynamic Damping Critical Angle of Attack Structural Damping Launch Vehicles Structural Response Aircraft Wings Wind Tunnel Tests numerical algorithms Free Vibrations numerical Analysis

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Material property identification of composite plates using neural network and evolution algorithm

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AIAA JOURNAL 2002年第9期40卷 1914-1916页

作者： Sung, BJ Park, JW Kim, YH Seoul Natl Univ Inst Adv Aerosp Technol Dept Aerosp Engn Seoul 151742 South Korea

Presents an effective nondestructive procedure for the identification of material properties of composite structures using the combined method of neural networks and an evolution algorithm. Identification procedure; N... 详细信息

关键词： Material Properties Neural Networks Dynamic Response Composite Structures numerical Analysis Perturbation Method numerical algorithms Aerospace Engineering Inverse Problems

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Simulation of laser plasma filamentation using adaptive mesh refinement

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JOURNAL OF COMPUTATIONAL PHYSICS 2002年第2期177卷 233-263页

作者： Dorr, MR Garaizar, FX Hittinger, JAF Lawrence Livermore Natl Lab Ctr Appl Sci Comp Livermore CA 94551 USA

We investigate the use of adaptive mesh refinement in the simulation of laser plasma filamentation. A numerical algorithm is constructed to solve model equations consisting of a fluid approximation of a quasineutral plasma combined with a paraxial light propagation model. The algorithm involves high-resolution plasma and light model discretizations on a block-structured, locally refined grid hierarchy, which is dynamically modified during the time integration to follow evolving fine-scale solution features. Comparisons of the efficiency of this approach to that of uniform grid calculations are presented. (C) 2002 Elsevier Science (USA).

关键词： laser plasma interaction numerical algorithms Godunov method adaptive mesh refinement plasma fluid model paraxial wave equation

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Application of large-eddy simulation to supersonic compression ramps

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AIAA JOURNAL 2002年第8期40卷 1574-1581页

作者： Rizzetta, DP Visbal, MR USAF Res Lab Computat Sci Branch Aeronaut Sci Div Wright Patterson AFB OH 45433 USA

Large-eddy simulations of supersonic compression-ramp flowfields were performed by a high-order numerical method, utilizing the Smagorinsky dynamic subgrid-scale model to account for spatially underresolved stresses. Computations were carried out at a freestream Mach number of 3.0 for ramp angles of 8, 16, 20, and 24 deg. Extensive comparisons are made between the respective solutions and available experimental data that were collected at higher Reynolds numbers. These include surface pressure, skin friction, and both mean and fluctuating velocity profiles. For the 24-deg case, a number of experimentally measured statistical quantities are compared to the simulation.

关键词： Direct numerical Simulation Freestream Mach Number Skin Friction Reynolds Averaged Navier Stokes Kinetic Energy Boundary Layer Thickness Compressibility Effect numerical algorithms Turbulence Models Vortex Breakdown

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GRAPE project

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JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS 2002年第1期149卷 131-145页

作者： Makino, J Univ Tokyo Sch Sci Dept Astron Bunkyo Ku Tokyo 1130033 Japan

We overview our GRAvity PipE (GRAPE) project to develop special-purpose computers for astrophysical N-body simulations. The basic idea of GRAPE is to attach a custom-build computer dedicated to the calculation of gravitational interaction between particles to a general-purpose programmable computer. By this hybrid architecture, we can achieve both a wide range of applications and very high peak performance. Our newest machine, GRAPE-6, achieved the peak speed of 32 Tflops, and sustained performance of 11.55 Tflops, for the total budget of about 4 million USD. We also discuss relative advantages of special-purpose and general-purpose computers and the future of high-performance computing for science and technology. (C) 2002 Elsevier Science B.V. All rights reserved.

关键词： computational science special-purpose computer numerical algorithms

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