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  • Open Access


    Coupled Electromechanical Optimization of Power Transmission Lines

    J.R. Jimenez-Octavio1, O. Lopez-Garcia2, E. Pilo1, A. Carnicero2

    CMES-Computer Modeling in Engineering & Sciences, Vol.25, No.2, pp. 81-98, 2008, DOI:10.3970/cmes.2008.025.081

    Abstract This paper presents a multidisciplinary design and optimization method of power transmission lines. This optimization method solves both mechanical and electrical problems by a new strongly coupled method that also optimizes the potential designs using a genetic algorithm. A multi-objective function is formulated to simplify a constrained typical optimization problem into an unconstrained one. The scope of this work is the sizing and configuration optimization problem with fixed topology. The method is applied to a railway overhead transmission line. The genetic algorithm is applied to mechanical, electrical and electromechanical optimization problems obtaining good results. Finally, More >

  • Open Access


    Numerical Identification of the Hydraulic Conductivity of Composite Anisotropic Materials

    S. D. Harris1, R. Mustata2, L. Elliott2, D. B. Ingham2, D. Lesnic2

    CMES-Computer Modeling in Engineering & Sciences, Vol.25, No.2, pp. 69-80, 2008, DOI:10.3970/cmes.2008.025.069

    Abstract Two homogeneous anisotropic materials are butted together to form a contact surface within a single composite material (the specimen). An inverse boundary element method (BEM) is developed to determine the components of the hydraulic conductivity tensor of each material and the position of the contact surface. A steady state flow is forced through the specimen by the application of a constant pressure differential on its opposite faces. Experimental measurements (simulated) of pressure and average hydraulic flux at exposed boundaries are then used in a modified least squares functional. This functional minimises the gap between the More >

  • Open Access


    A Meshless Modeling of Dynamic Strain Localization in Quasi-Brittle Materials Using Radial Basis Function Networks

    P. Le1, N. Mai-Duy2, T. Tran-Cong3, G. Baker4

    CMES-Computer Modeling in Engineering & Sciences, Vol.25, No.1, pp. 43-68, 2008, DOI:10.3970/cmes.2008.025.043

    Abstract This paper describes an integrated radial basis function network (IRBFN) method for the numerical modelling of the dynamics of strain localization due to strain softening in quasi-brittle materials. The IRBFN method is a truly meshless method that is based on an unstructured point collocation procedure. We introduce a new and effective regularization method to enhance the performance of the IRBFN method and alleviate the numerical oscillations associated with weak discontinuity at the elastic wave front. The dynamic response of a one dimensional bar is investigated using both local and non-local continuum models. Numerical results, which More >

  • Open Access


    Stable PDE Solution Methods for Large Multiquadric Shape Parameters

    Arezoo Emdadi1, Edward J. Kansa2, Nicolas Ali Libre1,3, Mohammad Rahimian1, Mohammad Shekarchi1

    CMES-Computer Modeling in Engineering & Sciences, Vol.25, No.1, pp. 23-42, 2008, DOI:10.3970/cmes.2008.025.023

    Abstract We present a new method based upon the paper of Volokh and Vilney (2000) that produces highly accurate and stable solutions to very ill-conditioned multiquadric (MQ) radial basis function (RBF) asymmetric collocation methods for partial differential equations (PDEs). We demonstrate that the modified Volokh-Vilney algorithm that we name the improved truncated singular value decomposition (IT-SVD) produces highly accurate and stable numerical solutions for large values of a constant MQ shape parameter, c, that exceeds the critical value of c based upon Gaussian elimination. More >

  • Open Access


    Meshless Local Petrov-Galerkin Method with Unity Test Function for Non-Isothermal Fluid Flow

    A. Arefmanesh1, M. Najafi1, H. Abdi1

    CMES-Computer Modeling in Engineering & Sciences, Vol.25, No.1, pp. 9-22, 2008, DOI:10.3970/cmes.2008.025.009

    Abstract The meshless local Petrov-Galerkin (MLPG) method with unity as the weighting function has been applied to the solution of the Navier-Stokes and energy equations. The Navier-Stokes equations in terms of the stream function and vorticity formulation together with the energy equation are solved for different test cases. This present study considers the implementation of the method on a non-isothermal lid-driven cavity flow, the lid-driven cavity flow with an inlet and outlet, and also on the non-isothermal flow over an obstacle. Nonuniform point distribution is employed for all the test cases for the numerical simulations. The More >

  • Open Access


    Numerical Computation of Electromagnetic Fields by the Time-Domain Boundary Element Method and the Complex Variable Method

    D. Soares Jr.1, M. P. Vinagre2

    CMES-Computer Modeling in Engineering & Sciences, Vol.25, No.1, pp. 1-8, 2008, DOI:10.3970/cmes.2008.025.001

    Abstract This work presents an alternative procedure to compute time-domain electromagnetic fields. The Boundary Element Method is here adopted to numerically analyze wave propagation problems, computing just a so-called primary field (either the electric or the magnetic field can be selected as primary field; the complementary field is here named secondary field). The secondary field is obtained following Maxwell's equations, i.e., considering space derivatives of the primary field (computed by the Complex Variable Method) and time integration procedures. This methodology is more efficient and flexible since fewer systems of equations must be solved at each time-step. More >

  • Open Access


    Molecular Dynamics Study of Size Effects and Deformation of Thin Films due to Nanoindentation

    Arun K. Nair1, Diana Farkas2, Ronald D. Kriz1

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 239-248, 2008, DOI:10.3970/cmes.2008.024.239

    Abstract The indentation response of Ni thin films of thicknesses in the nano scale was studied using molecular dynamics simulations with embedded atom method (EAM) interatomic potentials. Simulations were performed in single crystal films in the [111] orientation with thicknesses of 7nm and 33nm. In the elastic regime, the loading curves observed start deviating from the Hertzian predictions for indentation depths greater than 2.5% of the film thickness. The observed loading curves are therefore dependent on the film thickness. The simulation results also show that the contact stress necessary to emit the first dislocation under the More >

  • Open Access


    DFT Studies on Ferroelectric Ceramics and Their Alloys: BaTiO3, PbTiO3, SrTiO3, AgNbO3, AgTaO3, PbxBa1-xTiO3 and SrxBa1-xTiO3

    Mustafa Uludoğan1, D. Paula Guarin1, Zully E. Gomez1, Tahir Cagin1, William A. Goddard III2

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 215-238, 2008, DOI:10.3970/cmes.2008.024.215

    Abstract Aiming at a presentation of the utility of the state of art of first-principles methods (PBE flavor of Density Functional Theory, DFT) in the area of materials science and engineering, we present our studies of the equation of state and ferroelectric-paraelectricphase transition in several ferroelectric systems, including BaTiO3, PbTiO3, SrTiO3, AgNbO3, PbxBa1-xTiO3 and SrxBa1-xTiO3. We also report the Born effective charges, optical dielectric constant, and phonon dispersion relation properties from Density Functional Perturbation Theory. Computed results are compared with other theoretical results (which were mostly on BaTiO3, PbTiO3, cubic SrTiO3 using various approaches, as well as experiments. The studies on More >

  • Open Access


    Effects of Dopants on the Mechanical Properties of Nanocrystalline Silicon Carbide Thin Film

    Liming Xiong1, Youping Chen1

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 203-214, 2008, DOI:10.3970/cmes.2008.024.203

    Abstract This paper presents the application of an atomistic field theory (AFT) in modeling and simulation of boron- , boron/nitrogen and silicon/nitrogen-doped nanocrystalline silicon carbide (B-, BN-, SiN-SiC). Intergranular glassy films (IGFs) and nano-sized pores have been obtained in triple junctions of the grains in nanocrystalline SiC (nc-SiC). Residual tensile stress in the SiC grains and compressive stress in the grain boundaries (GBs) are observed. Under uniaxial tension, the constitutive responses of nanocrystalline SiC were reproduced from the simulations. It is found that the mechanical properties of nanocrystalline SiC are strongly dependent on the compositions of More >

  • Open Access


    Coupled Atomistic/Continuum Simulation based on Extended Space-Time Finite Element Method

    Shardool U. Chirputkar1, Dong Qian2

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 185-202, 2008, DOI:10.3970/cmes.2008.024.185

    Abstract A multiscale method based on the extended space-time finite element method is developed for the coupled atomistic/continuum simulation of nanoscale material systems. Existing single scale approach such as the finite element method has limited capability of representing the fine scale physics in both the spatial and temporal domains. This is a major disadvantage for directly incorporating FEM in coupled atomistic/continuum simulations as it results in errors such as spurious wave reflections at the atomistic/continuum interface. While numerous efforts have been devoted to eliminating the interfacial mismatch effects, less attention has been paid to developing fine More >

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