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numerical analysis of non-proportional biaxial reverse experiments with a two-surface anisotropic cyclic plasticity-damage approach

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COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2024年 419卷

作者： Wei, Zhichao Gerke, Steffen Bruenig, Michael Univ Bundeswehr Munchen Inst Mech & Statik Werner Heisenberg Weg 39 D-85577 Neubiberg Germany

This paper deals with the numerical analysis of ductile damage and fracture behavior under non -proportional biaxial reverse loading conditions. A two-surface anisotropic cyclic elastic-plastic-damage continuum model is adequately presented, which takes into account the Bauschinger effect, the stress-differential effect, and the change of hardening rate after reverse loading. An efficient Euler explicit numerical integration algorithm, based on the inelastic (plastic or plastic -damage) predictor-elastic corrector approach, is utilized to analyze the stress and finite strain loading histories. Detailed discussions are provided on different numerical integration-related consistent tangent operators that achieve convergence within the global Newton-Raphson scheme. The proposed continuum model is implemented into the commercial software Ansys as a user-defined subroutine (UMAT). Furthermore, the novel non-proportional biaxial tensile reverse experiments are performed to validate the proposed continuum model. The associated numerical simulations investigate the stability and accuracy of the proposed algorithm and material model.

关键词： Ductile damage and fracture Reverse loading Non-proportional biaxial experiments numerical algorithm Finite strains

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Novel numerical inversions of two circular-arc radon transforms in Compton scattering tomography

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INVERSE PROBLEMS IN SCIENCE AND ENGINEERING 2012年第6期20卷 809-839页

作者： Rigaud, Gael Nguyen, Mai K. Louis, Alfred K. ETIS ENSEA Univ Cergy Pontoise CNRS F-95000 Cergy Pontoise France Univ Saarland Fachbereich Math D-66041 Saarbrucken Germany

Compton scattering tomography (CST) is an alternative imaging process which reconstructs, in a two-dimensional slice, the electron density of an object by collecting radiation emitted from an external source and scattered throughout this object. The collected data at specific scattering energies appears essentially as the integral of the electron density on definite families of arcs of circles. Reconstruction of the unknown electron density is achieved by the inversion of the corresponding circular-arcs Radon transforms (CART). We review two existing CST modalities, their corresponding CART and establish their numerical inversion algorithms in the formalism of the so-called circular harmonic decomposition (CHD) for a function. The quality of the reconstructed images is illustrated by numerical simulations on test phantoms. Comparison with standard tomography performances demonstrates the efficiency and interest of this inversion method via CHD in imaging science such as biomedical imaging and non-destructive industrial testing.

关键词： compton scattering tomography inverse problems numerical algorithm biomedical imaging non-destructive testing

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A numerical procedure for analysing soil venting wells

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TRANSPORT IN POROUS MEDIA 2004年第3期57卷 297-312页

作者： Slodicka, M Univ Ghent Dept Math Anal Fac Engn B-9000 Ghent Belgium

Soil venting wells are difficult to analyse because flow occurs against a constant pressure. Here this difficulty is handled with a physically realistic but mathematically difficult nonlocal wellbore boundary condition ( BC). It is assumed that the air pressure inside the well is constant in space but time varying in an unknown fashion. A continuity equation is adopted at the boundary of the well which assumes the total well discharge consists of two parts: in flow from the surrounding unsaturated zone and release from wellbore storage. An efficient numerical algorithm is designed for dealing with the BCs at the well. The scheme is tested on two examples: the first is a simple problem with a known solution and the second problem is based on realistic data. The proposed method enables the accurate prediction of the time required to reach close to a steady state.

关键词： pneumatic well nonlocal boundary condition numerical algorithm

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numerical modeling of transverse mode competition in strongly pumped multimode fiber lasers and amplifiers

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OPTICS EXPRESS 2007年第6期15卷 3236-3246页

作者： Gong, Mali Yuan, Yanyang Li, Chen Yan, Ping Zhang, Haitao Liao, Suying Tsinghua Univ Dept Precis Instruments State Key Lab Tribol Ctr Photon & Elect Beijing 100084 Peoples R China

A model based on propagation-rate equations with consideration of transverse gain distribution is built up to describe the transverse mode competition in strongly pumped multimode fiber lasers and amplifiers. An approximate practical numerical algorithm by multilayer method is presented. Based on the model and the numerical algorithm, the behaviors of multitransverse mode competition are demonstrated and individual transverse modes power distributions of output are simulated numerically for both fiber lasers and amplifiers under various conditions. (c) 2007 Optical Society of America.

关键词： .Equations modes output power multimode fiber lasers amplifiers mode competition transverse gain numerical algorithm individual transverse power distributions Tünnermann

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numerical Laplace inversion in problems of elastodynamics: Comparison of four algorithms

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ADVANCES IN ENGINEERING SOFTWARE 2017年 113卷 120-129页

作者： Adamek, Vitezslav Vales, Frantisek Cerv, Jan Univ West Bohemia NTIS Univ 8 Plzen 30614 Czech Republic AS CR Inst Thermomech Vvi Veleslavinova 11 Plzen 30114 Czech Republic AS CR Inst Thermomech Vvi Dolejskova 1402-5 Prague 18200 8 Czech Republic

The objective of this work is to find a suitable algorithm for numerical Laplace inversion which could be used for effective and precise solution of elastodynamic problems. For this purpose, the capabilities of four algorithms are studied using three transforms resulted from analytical solutions of longitudinal waves in a thin rod, flexural waves in a thin beam and plane waves in a strip. In particular, the Gaver-Stehfest algorithm, the Gaver-Wynn's rho algorithm, the Fixed-Talbot algorithm and the FFT algorithm combined with Wynn's epsilon accelerator are tested. The codes written in Maple 16 employing multi-precision computations are presented for each method. Given the results obtained, the last mentioned algorithm proves to be the best. It is most efficient and it gives results of reasonable accuracy nearly for all tested times ranging from 3 x 10(-7) s to 3 x 10(3) s. (C) 2016 Civil-Comp Ltd. and Elsevier Ltd. All rights reserved.

关键词： Inverse Laplace transform numerical algorithm Wave propagation Multi-precision computation Maple code

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numerical approximation of optimal control for distributed diffusion Hopfield neural networks

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INTERNATIONAL JOURNAL FOR numerical METHODS IN ENGINEERING 2007年第3期69卷 443-468页

作者： Wang, Q. -F. Chinese Univ Hong Kong Dept Automat & Comp Aided Engn Shatin Hong Kong Peoples R China

This work presents a numerical approximation of optimal control problems for non-linear distributed Hopfield Neural Network equations with diffusion term. For one spatial dimensional case, a semi-discrete numerical algorithm was constructed to find optimal control variable using finite element discretization, updated conjecture gradient iteration method. Furthermore, experiments demonstration will be implemented to show the effectiveness and stability through 3D graphics simulations. Copyright (c) 2006 John Wiley & Sons, Ltd.

关键词： neural networks optimal control numerical algorithm finite element methods

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A new numerical method for the boundary optimal control problems of the heat conduction equation

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INTERNATIONAL JOURNAL FOR numerical METHODS IN ENGINEERING 2002年第7期53卷 1593-1613页

作者： Park, HM Lee, WJ Sogang Univ Dept Chem Engn Map Gu Seoul South Korea

A new numerical method is developed for the boundary optimal control problems of the heat conduction equation in the present paper. When the boundary optimal control problem is solved by minimizing the objective function employing a conjugate-gradient method, the most crucial step is the determination of the gradient of objective function usually employing either the direct differentiation method or the adjoint variable method. The direct differentiation method is simple to implement and always yields accurate results, but consumes a large amount of computational time. Although the adjoint variable method is computationally very efficient, the adjoint variable does not have sufficient regularity at the boundary for the boundary optimal control problems. As a result, a large numerical error is incurred in the evaluation of the gradient function, resulting in premature termination of the conjugate gradient iteration. In the present investigation, a new method is developed that circumvents this difficulty with the adjoint variable method by introducing a partial differential equation that describes the temporal and spatial dynamics of the control variable at the boundary. The present method is applied to the Neumann and Dirichlet boundary optimal control problems, respectively, and is found to solve the problems efficiently with sufficient accuracy. Copyright (C) 2001 John Wiley Sons, Ltd.

关键词： boundary control numerical algorithm regularization

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On numerical solving a rigid inclusions problem in 2D elasticity

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ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND PHYSIK 2017年第1期68卷 1-18页

作者： Rudoy, Evgeny Lavrentyev Inst Hydrodynam SB RAS Novosibirsk 630090 Russia Novosibirsk State Univ Novosibirsk 630090 Russia

A 2D elastic problem for a body containing a set of bulk and thin rigid inclusions of arbitrary shapes is considered. It is assumed that rigid inclusions are bonded into elastic matrix. To state the equilibrium problem, a variational approach is used. The problem is formulated as a problem of minimization of the energy functional over the set of admissible displacements. Moreover, it is equivalent to a variational equality which holds for test functions belonging to the subspace of functions with the prescribed rigid displacement structure on the inclusions. We propose a novel algorithm of solving the equilibrium problem. The algorithm is based on reducing the original problem to a system of the Dirichlet and Neumann problems. A numerical examination is carried out to demonstrate the efficiency of the proposed technique.

关键词： Bulk rigid inclusion Thin rigid inclusion numerical algorithm Variational approach FEM

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Rocking sensitivity of a dual-block stack - numerical simulation and experimental evidence

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EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS 2024年第1期53卷 366-391页

作者： Ceh, Nina Jelenic, Gordan Bicanic, Nenad Univ Rijeka Fac Civil Engn Radmile Matejcic 3 Rijeka 51000 Croatia

Historic monuments, drywall structures, and graphite blocks in AGR nuclear power plants are block-like structures that have to withstand rocking when subject to seismic excitation of their base, which can lead to overturning of some of their components and results in the collapse of the whole structure. We revisit the known nonlinear equations of motion for a dual-block stack and present the conditions for transition between the eight possible rocking configurations (due to initiation of rocking, opening of new contacts, and collisions between blocks). An algorithm for the numerical simulation of rocking of the dual-block stack is developed using the Newmark integration method, the Newton-Raphson iteration method, and a novel contact detection and resolution procedure. The algorithm is used to evaluate rocking stability of five dual-block stacks, one of which is compared to the results available in the literature. In parallel, a novel experimental program is designed and implemented, to validate the numerically obtained results using a shaking table. While most of the excitation conditions leading to stable rocking and limit values leading to overturning have been successfully validated, some discrepancies between the numerically and experimentally obtained results still exist and point to the need for improvement of the algorithm used, possibly through a more realistic energy-loss mechanism. Most importantly, we have confirmed the known theoretical prediction that splitting a single block into two half-size blocks benefits its rocking stability.

关键词： dual-block stack numerical investigation numerical algorithm partial overturning rocking stability assessment total overturning

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A general technique for assessing the numerical accuracy of solute transport models

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WATER RESOURCES RESEARCH 1999年第12期35卷 3961-3966页

作者： Ruan, F McLaughlin, D Li, SG Portland State Univ Dept Civil Engn Portland OR 97207 USA GeoQuest Schlumberger Adv Technol Houston TX 77056 USA MIT Dept Civil & Environm Engn Cambridge MA 02139 USA

This note describes a procedure for evaluating the accuracy of numerical solute transport models in situations where exact closed-form solutions are difficult or even impossible to obtain. The procedure attempts to match a specified closed-form "test solution" by adding forcing terms to the original equation, which is solved numerically. The quality of the match provides valuable information about the performance of the numerical algorithm. We illustrate this "prescribed forcing method" with an example which simulates solute transport in a heterogeneous velocity field. The numerical solver considered in the example is based on the Eulerian-Lagrangian method with linear velocity and concentration interpolation. Two test solutions of different degrees of difficulty are considered. Differences between the exact and numerical test solutions for the example clearly reveal the influence of grid resolution on model accuracy. The example demonstrates that the prescribed forcing method can be used to assess numerical accuracy in practical situations where model inputs are highly variable and the true solution is unknown.

关键词： .solute transport cult solver grid resolution velocity field closed-form test forcing terms original equation numerical algorithm test solutions numerical solutions

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