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  • Open Access

    ARTICLE

    A Spectral Boundary Element Method for Scattering Problems

    J. Tausch1, J. Xiao2

    CMES-Computer Modeling in Engineering & Sciences, Vol.58, No.3, pp. 221-246, 2010, DOI:10.3970/cmes.2010.058.221

    Abstract A fast method for the computation of layer potentials that arise in acoustic scattering is introduced. The principal idea is to split the singular kernel into a smooth and a local part. The potential due to the smooth part is discretized by a Nyström method and is evaluated efficiently using a sequence of FFTs. The potential due to the local part is approximated by a truncated series in the mollification parameter. The smooth approximation of the kernel is obtained by multiplication of its Fourier transform with a filter. We will show that for a rational filter the smooth part and… More >

  • Open Access

    ARTICLE

    Locking-free Thick-Thin Rod/Beam Element for Large Deformation Analyses of Space-Frame Structures, Based on the Reissner Variational Principle and A Von Karman Type Nonlinear Theory

    Y.C. Cai1,2, J.K. Paik3, S.N. Atluri4

    CMES-Computer Modeling in Engineering & Sciences, Vol.58, No.1, pp. 75-108, 2010, DOI:10.3970/cmes.2010.058.075

    Abstract This paper presents a new shear flexible beam/rod element for large deformation analyses of space-frame structures comprising of thin or thick members, based on the Reissner variational principle and a von Karman type nonlinear theory of deformation in the co-rotational reference frame of the present beam element. The C0continuous trial functions for transverse rotations in two independent directions are used over each element, to derive an explicit expression for the (16x16)symmetrictangent stiffness matrix of the beam element in the co-rotational reference frame. When compared to the primal approach wherein C1continuous trial functions for transverse displacements over each element are necessary,… More >

  • Open Access

    ARTICLE

    BEM Solutions for 2D and 3D Dynamic Problems in Mindlin's Strain Gradient Theory of Elasticity

    A. Papacharalampopoulos2, G. F. Karlis2, A. Charalambopoulos3, D. Polyzos4

    CMES-Computer Modeling in Engineering & Sciences, Vol.58, No.1, pp. 45-74, 2010, DOI:10.3970/cmes.2010.058.045

    Abstract A Boundary Element Method (BEM) for solving two (2D) and three dimensional (3D) dynamic problems in materials with microstructural effects is presented. The analysis is performed in the frequency domain and in the context of Mindlin's Form II gradient elastic theory. The fundamental solution of the differential equation of motion is explicitly derived for both 2D and 3D problems. The integral representation of the problem, consisting of two boundary integral equations, one for displacements and the other for its normal derivative is exploited for the proposed BEM formulation. The global boundary of the analyzed domain is discretized into quadratic line… More >

  • Open Access

    ARTICLE

    Convergence of Electromagnetic Problems Modelled by Discrete Geometric Approach

    Lorenzo Codecasa1, Francesco Trevisan2

    CMES-Computer Modeling in Engineering & Sciences, Vol.58, No.1, pp. 15-44, 2010, DOI:10.3970/cmes.2010.058.015

    Abstract This paper starts from the spatial discretization of an electromagnetic problem over pairs of oriented grids, one dual of the other, according to the so called Discrete Geometric Approach(DGA) to computational electromagnetism; the Cell Method or the Finite Integration Technique are examples of such an approach. The core of the work is providing for the first time a convergence analysis when the discrete counter-parts of constitutive relations are computed by means of an energetic framework. More >

  • Open Access

    ARTICLE

    New Interpretation to Variational Iteration Method: Convolution Iteration Method Based on Duhamel's Principle for Dynamic System Analysis

    Yunhua Li1,2, Yunze Li3, Chieh-Li Chen4, Cha’o-Kuang Chen5

    CMES-Computer Modeling in Engineering & Sciences, Vol.58, No.1, pp. 1-14, 2010, DOI:10.3970/cmes.2010.058.001

    Abstract Addressing the identification problem of the general Lagrange multiplier in the He's variational iteration method, this paper proposes a new kind of method based on Duhamel's principle for the dynamic system response analysis. In this method, we have constructed an analytical iteration formula in terms of the convolution for the residual error at the nth iteration, and have given a new interpretation to He's variational iteration method. The analysis illustrates that the computational result of this method is equal to that of He's variational iteration method on the assumption of considering the impulse response of the linear parts, or equal… More >

  • Open Access

    ARTICLE

    Shell-specific Interpolation of Measured 3D Displacements, for Micromechanics-Based Rapid Safety Assessment of Shotcrete Tunnels

    S. Ullah1, B. Pichler1, S. Scheiner1,2, C. Hellmich1,3

    CMES-Computer Modeling in Engineering & Sciences, Vol.57, No.3, pp. 279-316, 2010, DOI:10.3970/cmes.2010.057.279

    Abstract Point-wise optical measurements of 3D displacement vectors over time are a key input for monitoring shotcrete tunnel shells during construction according to the New Austrian Tunnelling Method (NATM). Aiming at estimation of the stresses prevailing in the highly loaded, hydrating material, we here deal with two different interpolation strategies for reconstructing, from measured displacement vectors, the 3D displacement field histories of the inner surface of the tunnel shell. The first approach considers spatial interpolation of displacement components in a fixed Cartesian base frame, while the second (new) approach refers to displacement components in a moving base frame consisting of vectors… More >

  • Open Access

    ARTICLE

    3D Higher-OrderX-FEM Model for the Simulation of Cohesive Cracks in Cementitious Materials Considering Hygro-Mechanical Couplings

    C. Becker1, S. Jox2, G. Meschke3

    CMES-Computer Modeling in Engineering & Sciences, Vol.57, No.3, pp. 245-278, 2010, DOI:10.3970/cmes.2010.057.245

    Abstract A three-dimensional numerical model based on the Extended Finite Element Method (X-FEM) is presented for the simulation of cohesive cracks in cementitious materials, such as concrete, in a hygro-mechanical framework. Enhancement functions for the small scale resolution of the displacement jump across cracks in the context of the X-FEM is used in conjunction with a higher order family of hierarchical shape functions for the representation of the large scale displacement field of the investigated structure. Besides the theoretical and computational formulation in a multiphase context, aspects of the implementation, such as integration and crack tracking algorithms, are discussed. Representative numerical… More >

  • Open Access

    ARTICLE

    Shape Memory Alloy: from Constitutive Modeling to Finite Element Analysis of Stent Deployment

    F. Auricchio1,2,3,4,1,5,1, M. Contisup>1,5,S. Morgantisup>1,, A. Reali1,2,3

    CMES-Computer Modeling in Engineering & Sciences, Vol.57, No.3, pp. 225-244, 2010, DOI:10.3970/cmes.2010.057.225

    Abstract The use of shape memory alloys (SMA) in an increasing number of applications in many fields of engineering, and in particular in biomedical engineering, is leading to a growing interest toward an exhaustive modeling of their macroscopic behavior in order to construct reliable simulation tools for SMA-based devices. In this paper, we review the properties of a robust three-dimensional model able to reproduce both pseudo-elastic and shape-memory effect; then we calibrate the model parameters on experimental data and, finally, we exploit the model to perform the finite element analysis of pseudo-elastic Nitinol stent deployment in a simplified atherosclerotic artery model. More >

  • Open Access

    ARTICLE

    Directional Cohesive Elements for the Simulation of Blade Cutting of Thin Shells

    A. Frangi1, M. Pagani1, U. Perego1, R. Borsari2

    CMES-Computer Modeling in Engineering & Sciences, Vol.57, No.3, pp. 205-224, 2010, DOI:10.3970/cmes.2010.057.205

    Abstract This paper is concerned with the finite element simulation of a thin membrane cutting by a sharp blade. Smeared crack finite element approaches appear to be unsuitable for this purpose, since very small elements would be required to conform to the sharp edge of the cutter. Furthermore, when the membrane material is very ductile, classical interface cohesive elements, where the cohesive forces are transmitted in the direction of the crack opening displacement, cannot correctly reproduce situations where the blade crosses the process zone. A simplified approach, based on the new concept of "directional" cohesive elements, is here proposed for a… More >

  • Open Access

    ARTICLE

    Locking-free Thick-Thin Rod/Beam Element Based on a von Karman Type Nonlinear Theory in Rotated Reference Frames For Large Deformation Analyses of Space-Frame Structures

    H.H. Zhu1, Y.C. Cai1,2, J.K. Paik3, S.N. Atluri4

    CMES-Computer Modeling in Engineering & Sciences, Vol.57, No.2, pp. 175-204, 2010, DOI:10.3970/cmes.2010.057.175

    Abstract This paper presents a new shear flexible beam/rod element for large deformation analyses of space-frame structures, comprising of thin or thick beams. The formulations remain uniformly valid for thick or thin beams, without using any numerical expediencies such as selective reduced integrations, etc. A von Karman type nonlinear theory of deformation is employed in the co-rotational reference frame of the present beam element, to account for bending, stretching, torsion and shearing of each element. Transverse shear strains in two independant directions are introduced as additional variables, in order to eliminate the shear locking phenomenon. An assumed displacement approach is used… More >

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