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  • Open AccessOpen Access

    ARTICLE

    Application of Multi-Region Trefftz Method to Elasticity

    J. Sladek1, V. Sladek1, V. Kompis2, R. Van Keer3
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 1-8, 2000, DOI:10.3970/cmes.2000.001.453
    Abstract This paper presents an application of a direct Trefftz method with domain decomposition to the two-dimensional elasticity problem. Trefftz functions are substituted into Betti's reciprocity theorem to derive the boundary integral equations for each subdomain. The values of displacements and tractions on subdomain interfaces are tailored by continuity and equilibrium conditions, respectively. Since Trefftz functions are regular, much less requirements are put on numerical integration than in the traditional boundary integral method. Then, the method can be utilized to analyse also very narrow domains. Linear elements are used for modelling of the boundary geometry and More >

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    1233

  • Open AccessOpen Access

    ARTICLE

    An Integer Programming Method for CPM Time-Cost Analysis

    A. P. Chassiakos, C. I. Samaras, D. D. Theodorakopoulos1
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 9-18, 2000, DOI:10.3970/cmes.2000.001.461
    Abstract Time and cost to complete a project is an important tradeoff problem in project planning and control. Existing methods have not provided an accepted solution in terms of both accuracy and efficiency. In an attempt to improve the solution process, a method is presented for developing optimal project time-cost curves based on CPM analysis. Using activity succession information, project paths are developed and duration is calculated. Following that, duration is reduced in an optimal way employing integer programming. Two alternative formulations are proposed which lead to corresponding algorithms, a progressive duration reduction and a direct More >

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    1881

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    1436

  • Open AccessOpen Access

    ARTICLE

    Crack Linkup by Stable Crack Growth

    L. Ma1, A.S. Kobayashi2, S. N. Atluri3, P.W. Tan4
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 19-26, 2000, DOI:10.3970/cmes.2000.001.471
    Abstract Experimentally determined Tε* and CTOA resistance curves were used to simulate numerically, stable crack growth and the ensuing crack linkup in 0.8 mm thick 2024-T3 aluminum tension specimen with multiple site damage (MSD) subjected to monotonically/cyclically increasing loading. The Tε* integral correctly predicted the crack growth and linkup history as well as the onset of rapid fracture in MSD specimens. The CTOA criterion also predicted the crack growth history but in its present form, could not predict crack linkup and rapid fracture. More >

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    1129

  • Open AccessOpen Access

    ARTICLE

    A 3-D Boundary Element Method for Dynamic Analysis of Anisotropic Elastic Solids1

    M. Kögl, L. Gaul2
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 27-44, 2000, DOI:10.3970/cmes.2000.001.479
    Abstract A Boundary Element formulation is presented for the solution of three-dimensional problems of anisotropic elastodynamics. Due to the complexity of the dynamic fundamental solutions for anisotropic materials and the resulting high computational costs, the approach at hand uses the fundamental solution of the static operator. This leads to a domain integral in the representation formula which contains the inertia term. The domain integral can be transformed to the boundary using the Dual Reciprocity Method. This results in a system of ordinary differential equations in time with time-independent matrices. Several general questions concerning the anisotropic solutions, More >

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    1610

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    1312

  • Open AccessOpen Access

    ARTICLE

    A Spectral Scheme to Simulate Dynamic Fracture Problems in Composites

    Changyu Hwang1, Philippe H. Geubelle2
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 45-56, 2000, DOI:10.3970/cmes.2000.001.497
    Abstract This paper presents the formulation and numerical implementation of a spectral scheme specially developed to simulate dynamic fracture events in unidirectional and cross-ply fiber-reinforced composites. The formulation is based on the spectral representation of the transversely isotropic elastodynamic relations between the traction stresses along the fracture plane and the resulting displacements. Example problems involving stationary or dynamically propagating cracks in fiber-reinforced composites are investigated and compared with reference solutions available in the literature and/or experimental observations. More >

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    1645

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    1352

  • Open AccessOpen Access

    ARTICLE

    Simulation of Dynamic Failure Evolution in Brittle Solids without Using Nonlocal Terms in the Strain-Stress Space

    Z. Chen1, W. Hu1, E.P. Chen2
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 57-62, 2000, DOI:10.3970/cmes.2000.001.509
    Abstract To simulate the dynamic failure evolution without using nonlocal terms in the strain-stress space, a damage diffusion equation is formulated with the use of a combined damage/plasticity model that was primarily applied to the case of rock fragmentation. A vectorized model solver is developed for large-scale simulation. Two-dimensional sample problems are considered to illustrate the features of the proposed solution procedure. It appears that the proposed approach is effective in simulating the evolution of localization, with parallel computing, in a single computational domain involving different lower-order governing differential equations. More >

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    1551

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    1183

  • Open AccessOpen Access

    ARTICLE

    MAADLY Spanning the Length Scales in Dynamic Fracture

    Farid F. Abraham1
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 63-70, 2000, DOI:10.3970/cmes.2000.001.515
    Abstract A challenging paradigm in the computational sciences is the coupling of the continuum, the atomistic and the quantum descriptions of matter for a unified dynamic treatment of a single physical problem. We described the achievement of such a goal. We have spanned the length scales in a concerted simulation comprising the finite-element method, classical molecular dynamics, quantum tight-binding dynamics and seamless bridges between these different physical descriptions. We illustrate and validate the methodology for crack propagation in silicon. More >

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    1524

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    1227

  • Open AccessOpen Access

    ARTICLE

    Damage Analysis for Mixed Mode Crack Initiation

    Y. Wei, C.L. Chow1, C.T. Liu2
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 71-78, 2000, DOI:10.3970/cmes.2000.001.523
    Abstract The paper presents a numerical simulation for mixed mode crack initiation based on the concepts of damage mechanics. A model with two scalar damage variables is introduced for characterization of damage in a material element. Then a tangent modulus tensor is derived for damage-coupled constitutive equations. A failure criterion is developed with the concept of damage accumulation not only to identify the location of damaged element where the crack initiation angle but also to determine the critical load for mixed mode fracture. The damage model developed is incorporated in a general-purpose finite element program ABAQUA More >

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    1468

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    1212

  • Open AccessOpen Access

    ARTICLE

    Wave Scattering by 2D Smooth Topographical Elastic Deformations Caused by a Point Blast Source

    Paulo Santos, Julieta António, António Tadeu1
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 79-98, 2000, DOI:10.3970/cmes.2000.001.531
    Abstract This paper presents the three-dimensional scattering field obtained when 2D smooth topographical deformations are subjected to a dilatational point load placed at some point in the medium. The solution is formulated using boundary elements for a wide range of frequencies and spatially harmonic line loads, which are then used to obtain time series by means of (fast) inverse Fourier transforms into space-time. The topographical surface is modeled with a number of boundary elements, defined according to the excitation frequency of the harmonic source, and in such a way that the free surface can be discretized More >

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    1515

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    1185

  • Open AccessOpen Access

    ARTICLE

    Structured Adaptive Control for Poorly Modeled Nonlinear Dynamical Systems

    John L. Junkins1, Kamesh Subbarao2, Ajay Verma3
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 99-118, 2000, DOI:10.3970/cmes.2000.001.551
    Abstract Model reference adaptive control formulations are presented that rigorously impose the dynamical structure of the state space descriptions of several distinct large classes of dynamical systems. Of particular interest, the formulations enable the imposition of exact kinematic differential equation constraints upon the adaptation process that compensates for model errors and disturbances at the acceleration level. Other adaptive control formulations are tailored for redundantly actuated and constrained dynamical systems. The utility of the resulting structured adaptive control formulations is studied by considering examples from nonlinear oscillations, aircraft control, spacecraft control, and cooperative robotic system control. The More >

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    1660

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    1181

  • Open AccessOpen Access

    ARTICLE

    Implicit Boundary Conditions for Direct Simulation Monte Carlo Method in MEMS Flow Predictions

    W.W. Liou1, Y.C. Fang1
    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.4, pp. 119-128, 2000, DOI:10.3970/cmes.2000.001.571
    Abstract A simple implicit treatment for the low speed inflow and outflow boundary conditions for the direct simulation Monte Carlo (DSMC) of the flows in microelectromechanical systems (MEMS) is proposed. The local mean flow velocity, temperature, and number density near the subsonic boundaries were used to determine the number of molecules entering the computational domain and their corresponding velocities at every sample average step. The proposed boundary conditions were validated against micro-Poiseuille flows and micro-Couette flows. The results were compared with analytical solutions derived from the Navier-Stokes equations using first-order and second order slip-boundary conditions. The More >

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