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  • Open Access


    Materials Modeling from Quantum Mechanics to The Mesoscale

    G. Fitzgerald1, G. Goldbeck-Wood2, P. Kung1, M. Petersen1, L. Subramanian1, J. Wescott2

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 169-184, 2008, DOI:10.3970/cmes.2008.024.169

    Abstract Molecular modeling has established itself as an important component of applied research in areas such as drug discovery, catalysis, and polymers. Algorithmic improvements to these methods coupled with the increasing speed of computational hardware are making it possible to perform predictive modeling on ever larger systems. Methods are now available that are capable of modeling hundreds of thousands of atoms, and the results can have a significant impact on real-world engineering problems. The article reviews some of the modeling methods currently in use; provides illustrative examples of applications to challenges in sensors, fuel cells, and More >

  • Open Access


    Strain Energy on the Surface of an Anisotropic Half-Space Substrate: Effect of Quantum-Dot Shape and Depth

    E. Pan1,2, Y. Zhang2, P. W. Chung3, M. Denda4

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 157-168, 2008, DOI:10.3970/cmes.2008.024.157

    Abstract Quantum-dot (QD) semiconductor synthesis is one of the most actively investigated fields in strain energy band engineering. The induced strain fields influence ordering and alignment, and the subsequent surface formations determine the energy bandgap of the device. The effect of the strains on the surface formations is computationally expensive to simulate, thus analytical solutions to the QD-induced strain fields are very appealing and useful. In this paper we present an analytical method for calculating the QD-induced elastic field in anisotropic half-space semiconductor substrates. The QD is assumed to be of any polyhedral shape, and its… More >

  • Open Access


    Buckling in Wurtzite-Like AlN Nanostructures and Crystals: Why Nano can be Different

    C. J. F. Solano, A. Costales, E. Francisco, A. Martín Pendás, Miguel A. Blanco1, K.-C. Lau, H. He, Ravindra Pandey2

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 143-156, 2008, DOI:10.3970/cmes.2008.024.143

    Abstract The buckling of hexagonal layers in bulk and nanostructures of AlN is analyzed in the framework of atomistic and first principles techniques. At ambient conditions, the wurtzite structure (B4) of AlN consists of buckled hexagons. On the other hand, a non-buckled Bk structure is found to be metastable at zero pressure, being favored at higher pressures. It is suggested that the energy ordering of B4 and Bk may change in finite systems; an assertion tested in this study by considering finite slabs, nanobelts, and nanorings, and comparing the results with the previous studies on small clusters,… More >

  • Open Access


    Phonon Transport and Thermal Conductivity Percolation in Random Nanoparticle Composites

    Weixue Tian1, Ronggui Yang2

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 123-142, 2008, DOI:10.3970/cmes.2008.024.123

    Abstract In this paper, we investigated the effective thermal conductivity of three dimensional nanocomposites composed of randomly distributed binary nanoparticles with large differences (contrast ratio) in their intrinsic (bulk) thermal conductivity. When random composites are made from particles with very different thermal conductivity (large contrast ratio), a continuous phase of high thermal conductivity constituent is formed when its volumetric concentration reaches beyond the percolation threshold. Such a continuous phase of material can provide a potentially low resistance pathway for thermal transport in random composites. The percolation theory predicts the thermal conductivity of the random composites to… More >

  • Open Access


    Evaluation of Effective Material Parameters of CNT-reinforced Composites via 3D BEM

    F.C. Araújo1, L.J. Gray2

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 103-122, 2008, DOI:10.3970/cmes.2008.024.103

    Abstract In recent years, carbon nanotubes (CNTs) have been widely employed to build advanced composites. In this work, a Boundary Element Method (BEM) is applied to 3D representative volume elements (RVEs) to estimate mechanical properties of CNT-based composites. To model the thin-walled nanotubes, special integration procedures for calculating nearly-strongly-singular integrals have been developed. The generic BE substructuring algorithm allows modeling complex CNT-reinforced polymers, containing any number of nanotubes of any shape (straight or curved). The subregion-by-subregion strategy, based on Krylov solvers, makes the independent generation, assembly, and storage of the many parts of the complete BE More >

  • Open Access


    Carbon Nanotube Transmission between Linear and Rotational Motions

    Hanqing Jiang1, Junqiang Lu2, Min-Feng Yu2, Yonggang Huang3

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 95-102, 2008, DOI:10.3970/cmes.2008.024.095

    Abstract The periodic lattice registry of multi-walled carbon nanotubes (MWCNTs) have been exploited for the possibilities of development of nanodevices. This paper studied the telescoping behaviors of double-walled carbon nanotubes (DWCNTs) by atomic-scale finite element and tight-bind Green function methods. It was found that telescoping a DWCNT (e.g., (6,3)/(12,6)) will induce a rotational motion of the inner CNT that has a chirl angle θ (0° < θ < 30°). This telescoping-induced rotational motion does not exist for armchair and zigzag DWCNTs due to the symmetry of CNTs. The rotational angle is completely determined by the chirality of More >

  • Open Access


    A Micromechanics Analysis of Nanoscale Graphite Platelet-Reinforced Epoxy Using Defect Green's Function

    B. Yang1,2, S.-C. Wong3, S. Qu3

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 81-94, 2008, DOI:10.3970/cmes.2008.024.081

    Abstract In the modeling of overall property of composites, the effect of particle interaction has been either numerically taken into account within a (representative) volume element of a small number of particles or neglected/ignored in order for efficient solution to a large system of particles. In this study, we apply the point-defect Green's function (GF) to take into account the effect of particle interaction. It is applicable to small volume fractions of particles (within 10 %). The high efficiency of the method enables a simulation of a large system of particles with generally elastic anisotropy, arbitrary… More >

  • Open Access


    A stabilized RBF collocation scheme for Neumann type boundary value problems

    Nicolas Ali Libre1,2, Arezoo Emdadi2, Edward J. Kansa3,4, Mohammad Rahimian2, Mohammad Shekarchi2

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.1, pp. 61-80, 2008, DOI:10.3970/cmes.2008.024.061

    Abstract The numerical solution of partial differential equations (PDEs) with Neumann boundary conditions (BCs) resulted from strong form collocation scheme are typically much poorer in accuracy compared to those with pure Dirichlet BCs. In this paper, we show numerically that the reason of the reduced accuracy is that Neumann BC requires the approximation of the spatial derivatives at Neumann boundaries which are significantly less accurate than approximation of main function. Therefore, we utilize boundary treatment schemes that based upon increasing the accuracy of spatial derivatives at boundaries. Increased accuracy of the spatial derivative approximation can be… More >

  • Open Access


    Line Search Partitioned Approach for Fluid-structure Interaction Analysis of Flapping Wing

    Tomonori Yamada1, Shinobu Yoshimura1

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.1, pp. 51-60, 2008, DOI:10.3970/cmes.2008.024.051

    Abstract Flight dynamics of flapping insects is still an open area of research, though it is well known that they can provide superior flight abilities such as hovering motion. The numerical analysis of flapping wing requires fluid-structure interaction (FSI) analysis to evaluate the effect of deformable wing on flight ability. Such FSI analysis is quite challenging because not only the tight coupling approach to predict flight ability accurately, but also the robust mesh control to trace the large motion of the wing with elastic deformation are required. A new iterative partitioned coupling algorithm for the FSI More >

  • Open Access


    A Hybrid Sensitivity Filtering Method for Topology Optimization

    S.Y. Wang1,2, K.M. Lim2,3, B.C. Khoo2,3, M.Y. Wang4

    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.1, pp. 21-50, 2008, DOI:10.3970/cmes.2008.024.021

    Abstract In topology optimization, filtering techniques have become quite popular in practice. In this paper, an accurate and efficient hybrid sensitivity filtering approach based on the traditional and bilateral sensitivity filtering approaches is proposed. In the present hybrid approach, the traditional sensitivity filter is applied to a sub-domain where numerical instabilities are likely to occur to overcome the numerical instabilites robustly. Filtering on mesh-independent holes identified by an image-processing-based technique is prohibited to reduce the computational cost. The bilateral approach is employed for the corresponding nearest neighboring elements of the mesh-independent holes to drive the 0-1 More >

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