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  • Open Access


    A Flexible Approach for the Calibration of Biplanar Radiography of the Spine on Conventional Radiological Systems

    Daniel C. Moura1, Jorge G. Barbosa1, Ana M. Reis2, João Manuel R. S. Tavares3

    CMES-Computer Modeling in Engineering & Sciences, Vol.60, No.2, pp. 115-138, 2010, DOI:10.3970/cmes.2010.060.115

    Abstract This paper presents a new method for the calibration of biplanar radiography that makes possible performing 3D reconstructions of the spine using conventional radiological systems. A novel approach is proposed in which a measuring device is used for determining focal distance and have a rough estimation of translation parameters. Using these data, 3D reconstructions of the spine with correct scale were successfully obtained without the need of calibration objects, something that was not previously achieved. For superior results, two optional steps may be executed that involve an optimisation of the geometrical parameters, followed by a… More >

  • Open Access


    Nonlinear Vibration of the Double-Beams Assembly Subjected to A.C. Electrostatic Force

    Shueei-Muh Lin1

    CMES-Computer Modeling in Engineering & Sciences, Vol.60, No.1, pp. 95-114, 2010, DOI:10.3970/cmes.2010.060.095

    Abstract In this study, the mathematical model of double-beams assembly subjected to the a.c. electrostatic force is established. This is helpful for designing sensors and actuators. The boundary condition of this system is nonlinear and time-dependent. Obviously, this system is very complicated. A new solution method is here developed to derive the analytical solution. Because the a.c. electrostatic force includes the static and harmonic forces, the system is divided into the nonlinear static and dynamic subsystems. The exact static solution is presented. In the other hand, the boundary conditions of the dynamic subsystem are nonlinear and More >

  • Open Access


    A Topology Optimization of Moderately Thick Plates Based on the Meshless Numerical Method

    S.L. Li1,2, S.Y. Long1, G.Y. Li1

    CMES-Computer Modeling in Engineering & Sciences, Vol.60, No.1, pp. 73-94, 2010, DOI:10.3970/cmes.2010.060.073

    Abstract A new implementation of topology optimization for the plate described by the Reissner-Mindlin theory based on the meshless natural neighbour Petrov-Galerkin method (NNPG) is proposed in this work. The objective is to produce the stiffest plate for a given volume by redistributing the material throughout the plate. We try to couple the advantages of the meshless numerical method with the topology optimization of moderately thick plate. The numerical approach presented here is based on the solid isotropic material with penalization (SIMP) formulation of the topology optimization problem. The natural neighbour interpolation shape function is employed More >

  • Open Access


    Mesh Effects in Predictions of Progressive Damage in 3D Woven Composites

    R. Valisetty1,2, A. Rajendran1,3, D. Grove2

    CMES-Computer Modeling in Engineering & Sciences, Vol.60, No.1, pp. 41-72, 2010, DOI:10.3970/cmes.2010.060.041

    Abstract A multi-scale model exhibiting progressive damage is considered for a 3D-woven composite. It is based on the evolution of some fundamental damage modes in a representative volume element (RVE) of a composite's woven architecture. The overall response of a woven composite due to a variety of damage modes is computationally obtained through a transformation field analysis (TFA) that is capable of quantifying the effects of spatial distribution of micro stresses and strains on strength. Since the model is computationally intensive, its numerical requirements are to be understood before it can successfully be used in design More >

  • Open Access


    A Meshless Collocation Method Based on the Differential Reproducing Kernel Approximation

    Shih-Wei Yang1, Yung-Ming Wang1, Chih-Ping Wu1,2, Hsuan-Teh Hu1

    CMES-Computer Modeling in Engineering & Sciences, Vol.60, No.1, pp. 1-40, 2010, DOI:10.3970/cmes.2010.060.001

    Abstract A differential reproducing kernel (DRK) approximation-based collocation method is developed for solving ordinary and partial differential equations governing the one- and two-dimensional problems of elastic bodies, respectively. In the conventional reproducing kernel (RK) approximation, the shape functions for the derivatives of RK approximants are determined by directly differentiating the RK approximants, and this is very time-consuming, especially for the calculations of their higher-order derivatives. Contrary to the previous differentiation manipulation, we construct a set of differential reproducing conditions to determine the shape functions for the derivatives of RK approximants. A meshless collocation method based on More >

  • Open Access


    An Enhanced Fictitious Time Integration Method for Non-Linear Algebraic Equations With Multiple Solutions: Boundary Layer, Boundary Value and Eigenvalue Problems

    Chein-Shan Liu1, Weichung Yeih2, Satya N. Atluri3

    CMES-Computer Modeling in Engineering & Sciences, Vol.59, No.3, pp. 301-324, 2010, DOI:10.3970/cmes.2010.059.301

    Abstract When problems in engineering and science are discretized, algebraic equations appear naturally. In a recent paper by Liu and Atluri, non-linear algebraic equations (NAEs) were transformed into a nonlinear system of ODEs, which were then integrated by a method labelled as the Fictitious Time Integration Method (FTIM). In this paper, the FTIM is enhanced, by using the concept of arepellorin the theory ofnonlinear dynamical systems, to situations where multiple-solutions exist. We label this enhanced method as MSFTIM. MSFTIM is applied and illustrated in this paper through solving boundary-layer problems, boundary-value problems, and eigenvalue problems with More >

  • Open Access


    High Velocity Impact Simulation of Brittle Materials with Node Separation Scheme in Parallel Computing Environment

    Ji Joong Moon1, Seung Jo Kim1, Minhyung Lee2

    CMES-Computer Modeling in Engineering & Sciences, Vol.59, No.3, pp. 275-300, 2010, DOI:10.3970/cmes.2010.059.275

    Abstract This paper describes the parallelization of contact/impact simulation for fracture modeling of brittle materials using a node separation scheme (NSS). We successfully demonstrated the fracture modeling of brittle materials using a cohesive fracture model. Since a NSS continuously generates new free surfaces as the computation progresses, the methodology requires increased computational time. To perform a simulation within a reasonable time period, a parallelization study is conducted. Particular methods for effective parallelization, especially for brittle materials, are described in detail. The crucial and most difficult strategy is the management of the data structure and communication needed More >

  • Open Access


    A Backward Group Preserving Scheme for Multi-Dimensional Backward Heat Conduction Problems

    Chih-Wen Chang1, Chein-Shan Liu2

    CMES-Computer Modeling in Engineering & Sciences, Vol.59, No.3, pp. 239-274, 2010, DOI:10.3970/cmes.2010.059.239

    Abstract In this article, we propose a backward group preserving scheme (BGPS) to tackle the multi-dimensional backward heat conduction problem (BHCP). The BHCP is well-known as severely ill-posed because the solution does not continuously depend on the given data. When eight numerical examples (including nonlinear and nonhomogeneous BHCP, and Neumann and Robin conditions of homogeneous BHCP) are examined, we find that the BGPS is applicable to the multi-dimensional BHCP. Even with noisy final data, the BGPS is also robust against disturbance. The one-step BGPS effectively reconstructs the initial data from the given final data, which with More >

  • Open Access


    Developing Mechanistic Understanding of Granular Behaviour in Complex Moving Geometry using the Discrete Element Method. Part A: Measurement and Reconstruction of TurbulaMixer Motion using Positron Emission Particle Tracking

    M. Marigo1,2, D. L. Cairns1, M. Davies1, M. Cook3,A. Ingram2,4,5, E. H. Stitt1

    CMES-Computer Modeling in Engineering & Sciences, Vol.59, No.3, pp. 217-238, 2010, DOI:10.3970/cmes.2010.059.217

    Abstract In this work the complex motion of the Turbulamixer has been measured by Multiple-Positron Emission Particle Tracking (Multiple PEPT) in order to set-up a DEM numerical model. Positron emitting radioactive tracers were attached to three of the pivot bearings on the shaft of the mixer to enable the rotation and translation of the mixer chamber to be tracked in the PEPT camera. The measured movement was mathematically reconstructed and imported into DEM in order to apply the same movement to the modelled vessel. The three-dimensional motion of particles in a vessel located in the Turbula More >

  • Open Access


    A new incompressible Navier-Stokes solver combining Fourier pseudo-spectral and immersed boundary methods

    F.P. Mariano1, L.Q. Moreira1, A. Silveira-Neto1, C.B. da Silva2, J.C.F. Pereira2

    CMES-Computer Modeling in Engineering & Sciences, Vol.59, No.2, pp. 181-216, 2010, DOI:10.3970/cmes.2010.059.181

    Abstract A new numerical methodology combining Fourier pseudo-spectral and immersed boundary methods - IMERSPEC - is developed for fluid flow problems governed by the incompressible Navier-Stokes equations. The numerical algorithm consists in a classical Fourier pseudo-spectral methodology using the collocation method where wall boundary conditions are modelled by using an immersed boundary method (IBM). The performance of that new methodology is exemplified in two-dimensional numerical simulations of Green-Taylor decaying vortex, lid-driven cavity and flow over a square cylinder. The convergence rate, the accuracy, the influence of the Reynolds number and the external domain size are analyzed. More >

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