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Evaluation of high-order spectral volume method for benchmark computational aeroacoustic problems

AIAA JOURNAL 2005年第2期43卷 337-348页

作者： Wang, ZJ Michigan State Univ Dept Mech Engn E Lansing MI 48824 USA

A time-accurate, high-order finite volume method named spectral volume (SV) method has been developed recently for conservation laws on unstructured grids and successfully demonstrated for Euler equations. In this paper, the SV method is evaluated for several benchmark problems in computational aeroacoustics (CAA) to demonstrate its potential for CAA applications. Both one-dimensional and two-dimensional problems are tested in the evaluation. It is shown that the higher-order SV schemes can achieve the same accuracy at a much lower cost than the lower-order ones.

关键词： Finite Volume Method Euler Equations Computational Aeroacoustics Unstructured Grid Riemann Problem Shape Functions Flow Conditions DG Method numerical algorithms Specific Heat

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Decrease of the effective Reynolds number with eddy-viscosity subgrid-scale modeling

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AIAA JOURNAL 2005年第2期43卷 437-439页

作者： Bogey, C Bailly, C Ecole Cent Lyon CNRS UMR 5509 Lab Mecan Fluides & Acoust F-69134 Ecully France

The present simulations of jets illustrate the effects of sub-grid modelingbased on eddy viscosity in LES. The effective flow Reynolds number is found to be dramaticallydecreased using the dynamic Smagorinsky model, whereas it seems to be preserved and to correspond tothe initial jet conditions using the selective filtering alone, This basic deficiency of theeddy-viscosity subgrid modeling can question its use for the study of free shear flows where theReynolds number is a key parameter, as for instance for the investigation of jet noise.

关键词： Reynolds Number Velocity Profiles Large Eddy Simulation Isotropic Turbulence Shear Layers Strouhal Numbers Turbulent Flow Overall Sound Pressure Level Navier Stokes Equations numerical algorithms

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Multiscale modeling for the long-term behavior of laminated composite structures

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AIAA JOURNAL 2005年第8期43卷 1815-1822页

作者： Muliana, A Haj-Ali, R Texas A&M Univ Dept Mech Engn College Stn TX 77843 USA Georgia Inst Technol Sch Civil & Environm Engn Atlanta GA 30332 USA

A multiscale modeling framework for the long-term behavior of fiber-reinforced-polymeric (FRIP) laminated. composite materials and structures is presented. Each unidirectional layer is idealized as a doubly periodic array, of rectangular fibers. The authors' previously developed unit cell with four fiber and matrix subcells is used. The, constitutive models for the elastic linear fiber and nonlinear viscoelastic matrix constituents are performed at the lowest level of the micromodel. This nonlinear micromodel is integrated with both, three-dimensional and shell-based finite elements. A plane-stress constraint is added to the three-dimensional micromodel in the case where shell elements are used. Long-term experimental creep data from the literature for graphite/epoxy are used in order to characterize the material properties. The effect of material nonlinearity on the long-term, behavior of FRP composites,is also investigated. Applications are presented for long-term creep responses of a notched composite panel under surface pressure and a single lap joint under tensile loads This modeling approach is general and can include temperature, moisture, and physical aging effects.

关键词： Composite Structures Fiber Reinforced Composites Transverse Shear Material Properties Creep Test Elastic Deformation Graphite Epoxy Composites numerical algorithms Structural Analysis Elastic Properties

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Finite deformations of metal cylinders subjected to electromagnetic fields and mechanical forces

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2005年第3期53卷 525-544页

作者： Bilyk, SR Ramesh, KT Wright, TW USA Res LabTD Weapons & Mat Res DirectorateWM AMSRDAR Aberdeen Proving Ground MD 21005 USA Johns Hopkins Univ Dept Engn Mech Baltimore MD 21218 USA

Strong electromagnetic (EM) fields coupled with mechanical loads may have a profound effect on deforming bodies. The continuum description of the plastic deformation of solids under electric fields and mechanical loads essentially involves the coupling of the field equations of continuum mechanics with Maxwell's equations. This analysis considers the effects of large EM fields on solid metal cylinders undergoing plastic deformations. Other researchers have used an electroplastic effect to explain previous EM and mechanically loaded experimental results. We examine whether it is 'necessary to invoke this controversial mechanism. First, we consider only EM loading and solve the transient EM distribution in a solid metal cylinder. This determines the EM time scales as compared to thermal diffusion time scales. Next, at the continuum level, we present the mechanical problem of quasi-static finite compressive deformations incorporating thermal expansion, strain hardening, strain rate sensitivity, thermal softening, and heat conduction. A viscoplastic model that is applicable over a wide range of strain rates (10(-4)-10(6) S-1) Characterizes the material response. Finally, we consider a metal cylinder subjected to uni-axial mechanical loading as well as high axial current pulses. The material is assumed, to be isotropic with. the plastic incompressibility constraint. The deformations are assumed to remain axisymmetric and no instabilities in the cylinder are considered. Coupled effects of Joule heating and the Lorentz force on the quasi-static deformations are examined. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： electromechanical processes strengthening and mechanisms thermomechanical finite deformation viscoplastic materials numerical algorithms

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Identification of point sets by quasidifferentiable functions

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OPTIMIZATION 2005年第4-5期54卷 411-420页

作者： Herklotz, A Luderer, B Chemnitz Univ Technol Dept Math D-09107 Chemnitz Germany

The aim of this article is to realize some ideas of Demyanov ( 2001) by means of numeric algorithms designed for quasidifferentiable functions.

关键词： quasidifferential calculus identification of point sets numerical algorithms

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Planar three-body problem in rendezvous coordinates

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2005年第3期28卷 553-557页

作者： Humi, M Worcester Polytech Inst Dept Math Sci Worcester MA 01609 USA

The plan of this Note is as follows. At first we present the general formulation of the problem and derive the orbit equations for the colliding bodies. We then recast the equations of motion in rendezvous coordinates and apply several transformations to simplify them. Two special cases of the general problem are considered next. The first is the restricted three-body problem. The second considers the case where two of the three bodies in the system have equal mass. Finally we discuss the numerical solution of the rendezvous equations and end up with summary and conclusions.

关键词： Earth Asteroids Satellites numerical Simulation numerical algorithms Keplerian Orbit Solar System

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Calculation of finite time ruin probabilities for some risk models

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INSURANCE MATHEMATICS & ECONOMICS 2005年第2期37卷 197-215页

作者： Cardoso, RMR Waters, HR Heriot Watt Univ Dept Actuarial Math & Stat Edinburgh EH14 4AS Midlothian Scotland Univ Nova Lisboa Fac Ciencia & Tecnol CMA P-2829516 Caparica Portugal Univ Nova Lisboa Fac Ciencia & Tecnol Dept Matemat P-2829516 Caparica Portugal

In this paper we discuss the numerical calculation of finite time ruin probabilities for two particular insurance risk models. The first model allows for the investment at a fixed rate of interest of the surplus whenever this is above a given level. This is related to a model studied by Embrechts and Schmidli [Embrechts, P., Schmidli, H., 1994. Ruin estimation for a general insurance risk model. Adv. Appl. Probability 26 (2), 404-422] and by Schmidli [Schmidli, H., 1994a. Corrected diffusion approximations for a risk process with the possibility of borrowing and investment. Schweizerische Vereinigung der Versicherungsmathematiker. Mitteilungen (1), 71-82;Schmidli, H., 1994b. Diffusion approximations for a risk process with the possibility of borrowing and investment. Commun. Stat. Stochastic Models 10 (2), 365-388]. Our second model is the classical risk model but with the insurer's premium rate depending on the level of the surplus. In our final section, we discuss the extension of the these models to allow for the parameters to change over time in a deterministic way. Our methodology for calculating finite time ruin probabilities is to bound the surplus process by discrete-time Markov chains;the average of the bounds gives an approximation to the ruin probability. This approach was used by the authors in a previous paper, Cardoso and Waters [Cardoso, R.M.R., Waters, H.R., 2003. Recursive calculation of finite time ruin probabilities under interest force. Insurance Math. Econ. 33 (3), 659-676], which considered a risk process with interest earned on the surplus. (c) 2004 Elsevier B.V. All rights reserved.

关键词： Ruin probability numerical algorithms Markov chains

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Computational experience in solving algebraic Riccati equations

Computational experience in solving algebraic Riccati equati...

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44th IEEE Conference on Decision Control/European Control Conference (CCD-ECC)

作者： Sima, Vasile Natl Inst Res & Dev Informat Bucharest 011455 Romania

ISBN: (纸本)0780395670

State-of-the-art, uni-processor algebraic Riccati equation solvers for automatic control computations are investigated and compared for various problem sizes. General-purpose SLICOT solvers are very efficient for small-size problems, but they cannot compete for larger problems with specialized solvers designed for certain problem classes, such as Newton solvers using low rank Cholesky factors of the solutions of Lyapunov equations built at each iteration.

关键词： algebraic Riccati equations numerical algorithms computer-aided control system design numerical linear algebra software library

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A provably convergent algorithm for transition-time optimization in switched systems

A provably convergent algorithm for transition-time optimiza...

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44th IEEE Conference on Decision Control/European Control Conference (CCD-ECC)

作者： Axelsson, Henrik Wardi, Yorai Egerstedt, Magnus Verriest, Erik Georgia Inst Technol Sch Elect & Comp Engn Atlanta GA 30332 USA

ISBN: (纸本)0780395670

This paper concerns a mode-sequencing and switching-time optimization problem defined on autonomous switched-mode hybrid dynamical systems. The design parameter consists of two elements: (i) the sequence of dynamic-response functions associated with the modes, and (ii) the duration of each mode. The sequencing element is a discrete parameter which may render the problem of computing the optimal schedule exponentially complex. Therefore we are not seeking a global minimum, but rather a local solution in a suitable sense. To this end we endow the parameter space with a local continuous structure which allows us to apply gradient-descent techniques. With this structure, the problem is cast in the form of a nonlinear-programming problem defined on a sequence of nested Euclidean spaces with increasing dimensions. We characterize suboptimality in an appropriate sense, define a corresponding convergence criterion, and devise a provably-convergent optimization algorithm.

关键词： hybrid systems switching modes optimal control gradient descent numerical algorithms

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The automated approach to the mode-matching and S-matrix techniques: From idea to realization

The automated approach to the mode-matching and S-matrix tec...

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5th International Conference on Antenna Theory and Techniques

作者： Kirilenko, A Kulik, D Rud, L Kulishenko, S Tkachenko, V NAS Ukraine Inst Radio Phys & Elect Kharkov Ukraine

ISBN: (纸本)078392613

An attempt of combining the efficiency of problem-oriented numerical algorithms with the generality of mesh methods is made. The automatic procedure of decomposition of complicated waveguide structures is developed. It takes into account peculiarities of the given problem (symmetries, uniformity and so on) and tries to find out the best possible solution. Presented approach is successfully applied to create the electromagnetic simulator Microwave Desktop 2 (MWD 2). It allows one to solve a wide range of electromagnetic problems from analysis to optimization.

关键词： mode-matching technique decomposition approach numerical algorithms waveguide components

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