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  • Open 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 >

  • Open 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 >

  • Open Access

    ARTICLE

    Solving Rolling Contact Problems Using Boundary Element Method and Mathematical Programming Algorithms

    José A. González, Ramón Abascal1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 141-150, 2000, DOI:10.3970/cmes.2000.001.443

    Abstract In this work an approach to the two-dimensional steady-state rolling contact problem, with and without force transmission, is presented. The problem is solved by the combination of the Boundary Element Method with a formulation of the variational inequalities that govern the problem in the contact area, producing finally a mathematical programming problem. This formulation avoids the direct use of the contact constrains, but it drives to the minimisation of a non-differentiable function, being necessary the use of an specific numerical tool as the modified Newton's method. More >

  • Open Access

    ARTICLE

    General Application of Numerical Green's Functions for SIF Computations With Boundary Elements

    S. Guimarães1, J.C.F. Telles2

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 131-139, 2000, DOI:10.3970/cmes.2000.001.433

    Abstract The paper discusses further applications of the hyper-singular boundary integral equation to obtain the Green's function solution to general geometry fracture mechanics problems, such as curved multifracture crack simulation, static and transient dynamic in 2-D, 3-D and plate bending problems. This numerical Green's function (NGF) is implemented into alternative boundary element computer programs, as the fundamental solution, to enhance the scope of alternative applications of the NGF procedure.
    The results to some typical linear fracture mechanics problems are presented. More >

  • Open Access

    ARTICLE

    BEM / FEM Comparison Studies for the Inelastic Dynamic Analysis of Thick Plates on Elastic Foundation

    C.P . Providakis1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 123-130, 2000, DOI:10.3970/cmes.2000.001.425

    Abstract Boundary and Finite Element methodologies for the determination of the inelastic response of thick plates resting on Winkler-type elastic foundations are compared and critically discussed. For comparison reasons the domain/boundary element and the finite element methodology use isoparametric elements of the same accuracy level. After a discretizaton of the integral equations of motion in both methodologies an efficient step-by-step time integration algorithm is used to solve the resulting matrix equations. Comparison studies are shown for impacted elastoplastic thick plates with smooth boundaries and supported on different Winkler-type foundations. The numerical results reveal that boundary element More >

  • Open Access

    ARTICLE

    A Numerical Method for Schwarz-Christoffel Conformal Transformation with Application to Potential Flow in Channels with Oblique Sub-channels

    P.M.J. Trevelyan1, L. Elliott1, D.B. Ingham1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 117-122, 2000, DOI:10.3970/cmes.2000.001.419

    Abstract The potential flow in a semi-infinite channel with multiple semi-infinite oblique sub-channels is determined using the Schwarz-Christoffel transformation and complex potential theory. The standard iterative technique, i.e. the Newton-Raphson method with the Jacobian matrix approximated by a finite-difference quotient matrix, was employed with an alternative integration region to that found elsewhere in the literature is employed after integrating across the boundaries to determine the Schwarz-Christoffel transformation parameters which solely depend on the dimensions of the region being considered. Each semi-infinte channel permits integration at infinity perpendicularly across the channel and sub-channels, yielding some analytical relationships… More >

  • Open Access

    ARTICLE

    An Inverse Boundary Element Method for Determining the Hydraulic Conductivity in Anisotropic Rocks

    R. Mustata1, S. D. Harris2, L. Elliott1, D. Lesnic1, D. B. Ingham1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 107-116, 2000, DOI:10.3970/cmes.2000.001.409

    Abstract An inverse boundary element method is developed to characterise the components of the hydraulic conductivity tensor K of anisotropic materials. Surface measurements at exposed boundaries serve as additional input to a Genetic Algorithm (GA) using a modified least squares functional that minimises the difference between observed and BEM-predicted boundary pressure and/or hydraulic flux measurements under current hydraulic conductivity tensor component estimates. More >

  • Open Access

    ARTICLE

    An Iterative Boundary Element Method for the Solution of a Cauchy Steady State Heat Conduction Problem

    N.S. Mera, L. Elliott, D.B. Ingham, D. Lesnic1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 101-106, 2000, DOI:10.3970/cmes.2000.001.403

    Abstract In this paper the iterative algorithm proposed by [Kozlov and Maz'ya (1990)] for the backward heat conduction problem is extended in order to solve the Cauchy steady state heat conduction problem and the accuracy, convergence and stability of the numerical algorithm are investigated. The numerical results which are obtained confirm that this new iterative BEM procedure is accurate, convergent and stable with respect to increasing the number of boundary elements and decreasing the amount of noise which is added into the input data. More >

  • Open Access

    ARTICLE

    Fracture Mechanics Analysis in 2-D Anisotropic Thermoelasticity Using BEM

    Y.C. Shiah1, C.L. Tan1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 91-99, 2000, DOI:10.3970/cmes.2000.001.393

    Abstract In the direct formulation of the boundary element method (BEM), a volume integral arises in the resulting integral equation if thermal effects are present. The steps to transform this volume integral into boundary ones in an exact analytical manner are reviewed in this paper for two- dimensional anisotropic thermoelasticity. The general applicability of the BEM algorithm for fracture mechanics applications is demonstrated by three crack problems with slanted cracks. The numerical results of the stress intensity factors are presented and compared with those obtained using superposition. More >

  • Open Access

    ARTICLE

    A Numerical Variational Approach for Rotor-Propeller Aerodynamics in Axial Flight

    F. Simonetti1, R. M. Ardito Marretta2

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 81-90, 2000, DOI:10.3970/cmes.2000.001.383

    Abstract Advanced propellers are being developed to improve the performance and fuel economy of future transport aircraft. To study them, various aerodynamic prediction models and systems (from theory to experiment) have been developed via several approaches (Free Wake Analysis, helicoidal source methods, scale model tests). This study focuses on the development of an efficient numerical method to predict the behaviour of rotor or propeller in forward flight. Based on a variational approach, the present numerical technique allows a significant reduction of computer resources used in the calculation of instantaneous velocities to determine the wake geometry and More >

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