N. Sageresan, R. Drathi

CMES-Computer Modeling in Engineering & Sciences, Vol.32, No.2, pp. 103-112, 2008, DOI:10.3970/cmes.2008.032.103

Abstract Crack propagation in concrete is computed with a simplified meshless method. The material is elastic of Neo-Hookian type until fracture. Then a discrete cohesive crack method is used. In the cohesive crack method, cohesive segments are introduced at the meshless nodes. No representation of the crack surface is needed. The method is well-suited for concrete since concrete develops many cracks. Mesh independent results are obtained due to the cohesive model that takes into account the correct energy dissipation during crack opening. We show the accuracy of our method by comparison to experimental data. More >

Delfim Soares Jr. ¹

CMES-Computer Modeling in Engineering & Sciences, Vol.32, No.2, pp. 57-68, 2008, DOI:10.3970/cmes.2008.032.057

Abstract In this work, a time-domain finite element -- boundary element iterative coupling technique is presented in order to analyse electromagnetic scattering from two-dimensional inhomogeneous objects. In the iterative coupling algorithm, the domain of the original problem is subdivided into sub-domains and each sub-domain is analysed independently (as an uncoupled model) taking into account successive renewals of variables at common interfaces. In order to improve the effectiveness of the iterative coupling approach, the evaluation of an optimised relaxation parameter is discussed, taking into account the minimisation of a square error functional. The algorithm that arises is More >

E. Ferretti¹, E. Casadio, A. Di Leo¹

CMES-Computer Modeling in Engineering & Sciences, Vol.30, No.3, pp. 163-190, 2008, DOI:10.3970/cmes.2008.030.163

Abstract In this study, the Cell Method (CM) is applied in order to investigate the failure mechanisms of masonry walls under shear force. The direction of propagation is computed step-wise by the code, and the domain is updated by means of a propagation technique of intra-element nodal relaxation with re-meshing. The crack extension condition is studied in the Mohr/Coulomb plane, using the criterion of Leon. The main advantage of using the CM for numerical analyses of masonry is that the mortar, the bricks and the interfaces between mortar and bricks can be modeled without any need… More >

A.I. Abreu¹, W.J. Mansur¹, D. Soares Jr^1,2, J.A.M. Carrer³

CMES-Computer Modeling in Engineering & Sciences, Vol.30, No.3, pp. 123-132, 2008, DOI:10.3970/cmes.2008.030.123

Abstract This paper is concerned with the numerical computation of space derivatives of a time-domain (TD-) Boundary Element Method (BEM) formulation for the analysis of scalar wave propagation problems. In the present formulation, the Convolution Quadrature Method (CQM) is adopted, i.e., the basic integral equation of the TD-BEM is numerically substituted by a quadrature formula, whose weights are computed using the Laplace transform of the fundamental solution and a linear multi-step method. In order to numerically compute space derivatives, the present work properly transforms the quadrature weights of the CQM-BEM, adopting the so-called Complex-Variable-Differentiation Method (CVDM). More >

S.S. Xu, Y. Dong, Y. Zhang

CMES-Computer Modeling in Engineering & Sciences, Vol.30, No.1, pp. 17-26, 2008, DOI:10.3970/cmes.2008.030.017

Abstract A meshless method for arbitrary crack growths is presented. The new method is based on a local partition of unity by introducing additional degrees of freedom that determine the opening of the crack. The crack is modeled with overlapping crack segments located at the nodes. The crack segments are rotated at directional changes of the principal tensile stress such that smearing of the crack is avoided. Such smearing occurs in fixed crack method probably because of inaccurate stress state around the crack tip when the crack propagates. The key feature of our method is that More >

Mira Mitra¹, S. Gopalakrishnan²

CMES-Computer Modeling in Engineering & Sciences, Vol.27, No.1&2, pp. 125-136, 2008, DOI:10.3970/cmes.2008.027.125

Abstract In this paper, the wave characteristics, namely, the spectrum and dispersion relations of multi-wall carbon nanotubes (MWNTs) are studied. The MWNTs are modeled as multiple thin shells coupled through van der Waals force. Each wall of the MWNT has three displacements, i.e, axial, circumferential and radial with variation along the axial and circumferential directions. The wave characteristics are obtained by transforming the governing differential wave equations to frequency domain via Fourier transform. This transformation is first done in time using fast Fourier transform (FFT) and then in one spatial dimension using Fourier series. These transformed equations More >

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 >

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 >

B. Srivathsa¹, N. Ramakrishnan²

CMC-Computers, Materials & Continua, Vol.7, No.1, pp. 9-24, 2008, DOI:10.3970/cmc.2008.007.009

Abstract An analytical model, describing an explosive compaction process performed axially on a powder assembly of cylindrical geometry, is discussed. The powder is encapsulated in a cylindrical metal container surrounded by an explosive pad, which is detonated parallel to the major axis of the compact. The pressure generated in the powder is a function of the nature and the thickness of the explosive material as well as the powder characteristics. The model is based on the principle of shock propagation in powder aggregate and, the detonation as well as the refraction wave characteristics of the explosives.… More >

Abdulnaser M. Alshoaibi^1,2, M. S. A. Hadi², A. K. Ariffin²

Structural Durability & Health Monitoring, Vol.3, No.1, pp. 15-28, 2007, DOI:10.3970/sdhm.2007.003.015

Abstract An adaptive finite element method is employed to analyze two-dimensional linear elastic fracture problems. The mesh is generated by the advancing front method and the norm stress error is taken as a posteriori error estimator for the h-type adaptive refinement. The stress intensity factors are estimated by a displacement extrapolation technique. The near crack tip displacements used are obtained from specific nodes of natural six-noded quarter-point elements which are generated around the crack tip defined by the user. The crack growth and its direction are determined by the calculated stress intensity factors as the maximum circumference More >