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  • Open Access


    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 method appears to be a… More >

  • Open Access


    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 between these parameters. The remainder… More >

  • Open Access


    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


    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


    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


    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 the three-dimensional vortex flow streaming… More >

  • Open Access


    A Boundary Element Model for Underwater Acoustics in Shallow Water

    J.A.F. Santiago1, L.C. Wrobel2

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 73-80, 2000, DOI:10.3970/cmes.2000.001.375

    Abstract This work presents a boundary element formulation for two-dimensional acoustic wave propagation in shallow water. It is assumed that the velocity of sound in water is constant, the free surface is horizontal, and the seabed is irregular. The boundary conditions of the problem are that the sea bottom is rigid and the free surface pressure is atmospheric.
    For regions of constant depth, fundamental solutions in the form of infinite series can be employed in order to avoid the discretisation of both the free surface and bottom boundaries. When the seabed topography is irregular, it is necessary to divide the… More >

  • Open Access


    Non-Isothermal Three-Dimensional Developments and Process Modeling of Composites: Flow/Thermal/Cure Formulations and Experimental Validations

    N. D. Ngo, K. K. Tamma1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 57-72, 2000, DOI:10.3970/cmes.2000.001.359

    Abstract In the process modeling via Resin Transfer Molding (RTM) for thick composite sections, multi-layer preforms with varying thermophysical characteristics across the different layers, or for geometrically complex mold geometries with varying thicknesses, the assumption of a thin shell-like geometry is no longer valid. The flow in the through thickness direction is no longer negligible and current practices of treating the continuously moving flow front as two-dimensional and the temperature and cure as three-dimensional are not representative of the underlying physics. In view of these considerations, in the present study, the focus is on the non-isothermal process modeling of composites employing… More >

  • Open Access


    New insights in nonlinear static stability analysis by the FEM

    B. Pichler1, H.A. Mang1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 43-55, 2000, DOI:10.3970/cmes.2000.001.345

    Abstract In order to avoid a fully nonlinear analysis to obtain stability limits on nonlinear load-displacement paths, linear eigenvalue problems may be used to compute estimates of such limits. In this paper an asymptotic approach for assessment of the errors resulting from such estimates is presented. Based on the consistent linearization of the geometrically nonlinear static stability criterion – the so-called consistently linearized eigenvalue problem – higher-order estimation functions can be calculated. They are obtained from a scalar post-calculation performed after the solution of the eigenproblem. Different extensions of these higher-order estimation functions are presented. An ab initio criterion for the… More >

  • Open Access


    Dynamics of Machinery 2D Elastic Casing, with Central Hole, Subject to an In-Plane Deflection-Dependent Rotating Load

    F. M. A. El-Saeidy1

    CMES-Computer Modeling in Engineering & Sciences, Vol.1, No.3, pp. 33-42, 2000, DOI:10.3970/cmes.2000.001.335

    Abstract In rotating radial ball bearings supported on elastic casings with the bearing outer ring lightly fitted into the housing, the force due to the ball elastic contact is indeed a rotating load rolling over the housing. For accurate estimation of the dynamic deformations of the casing annulus (hole), which in turn affect the bearing tolerances and hence the magnitudes of the generated forces, effect of the load rotation (motion) should be considered. Considering the integral casing and the outer ring to be a plate, an isoparametric plane stress finite-element (FE) based analytical procedure is presented for the dynamic analysis of… More >

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