K. Han¹, Y. T. Feng¹, D. R. J. Owen¹

CMES-Computer Modeling in Engineering & Sciences, Vol.49, No.2, pp. 143-162, 2009, DOI:10.3970/cmes.2009.049.143

Abstract Motivated by Hottel's crossed-string method, this paper presents an accurate algorithm for the evaluation of the geometric view factors in a randomly packed bed of circular particles of various sizes. The radiative heat exchange can thus be predicted accurately. The solution procedure is illustrated and the solution accuracy is assessed via a numerical example. More >

Liviu Marin¹

CMES-Computer Modeling in Engineering & Sciences, Vol.46, No.3, pp. 221-254, 2009, DOI:10.3970/cmes.2009.046.221

Abstract We investigate the stable numerical reconstruction of an unknown portion of the boundary of a two-dimensional domain occupied by a functionally graded material (FGM) from a given boundary condition on this part of the boundary and additional Cauchy data on the remaining known portion of the boundary. The aforementioned inverse geometric problem is approached using the method of fundamental solutions (MFS), in conjunction with the Tikhonov regularization method. The optimal value of the regularization parameter is chosen according to Hansen's L-curve criterion. Various examples are considered in order to show that the proposed method is numerically stable with respect to… More >

Y.M. Zhang¹, Y. Gu¹, J.T. Chen²

CMES-Computer Modeling in Engineering & Sciences, Vol.45, No.3, pp. 227-248, 2009, DOI:10.3970/cmes.2009.045.227

Abstract The accurate evaluation of nearly singular integrals is one of the major concerned problems in the boundary element method (BEM). Although the current methods have achieved great progress, it is often possible only for problems defined in the simplest geometrical domains when the nearly singular integrals need to be calculated. However, engineering processes occur mostly in complex geometrical domains, and always, involve nonlinearities of the unknown variables and its derivatives. Therefore, effective methods of dealing with nearly singular integrals for such practical problems are necessary and need to be further investigated. In this paper, a general strategy based on a… More >

Francisco P. M. Oliveira¹, João Manuel R. S. Tavares¹

CMES-Computer Modeling in Engineering & Sciences, Vol.43, No.1, pp. 91-110, 2009, DOI:10.3970/cmes.2009.043.091

Abstract This paper presents a new methodology to establish the best global match of objects' contours in images. The first step is the extraction of the sets of ordered points that define the objects' contours. Then, by using the curvature value and its distance to the corresponded centroid for each point, an affinity matrix is built. This matrix contains information of the cost for all possible matches between the two sets of ordered points. Then, to determine the desired one-to-one global matching, an assignment algorithm based on dynamic programming is used. This algorithm establishes the global matching of the minimum global… More >

S. Tangaramvong¹, F. Tin-Loi¹

CMES-Computer Modeling in Engineering & Sciences, Vol.42, No.3, pp. 217-256, 2009, DOI:10.3970/cmes.2009.042.217

Abstract Classical limit analysis is extended to include the effects of 2nd-order geometric and material nonlinearities, as well as the inclusion of limited ductility constraints. For the class of frame structures considered, the material constitutive model adopted can simultaneously accommodate the effects of combined axial and flexural force as well as local softening instability through the use of piecewise linearized yield surfaces. The main feature of the approach developed is to compute, in a single step, an upper bound to the maximum load. Corresponding displacements and stresses can be obtained as a by-product of the analysis. The problem is formulated as… More >

P. Bettini, E. Brusa, M. Munteanu, R. Specogna, F. Trevisan¹

CMES-Computer Modeling in Engineering & Sciences, Vol.33, No.3, pp. 215-242, 2008, DOI:10.3970/cmes.2008.033.215

Abstract Electrostatic microactuator is a paradigm of MEMS. Cantilever and double clamped microbeams are often used in microswitches, microresonators and varactors. An efficient numerical prediction of their mechanical behaviour is affected by the nonlinearity of the electromechanical coupling. Sometimes an additional nonlinearity is due to the large displacement or to the axial-flexural coupling exhibited in bending. To overcome the computational limits of the available numerical methods two new formulations are here proposed and compared. Modifying the classical beam element in the Finite Element Method to allow the implementation of a \emph {Non incremental sequential approach} is firstly proposed. The so-called \emph… More >

L. Codecasa¹, R. Specogna², F. Trevisan³

CMES-Computer Modeling in Engineering & Sciences, Vol.31, No.3, pp. 129-144, 2008, DOI:10.3970/cmes.2008.031.129

Abstract In the paper we introduce a methodology to construct discrete constitutive matrices relating magnetic fluxes with magneto motive forces (reluctance matrix) and electro motive forces with currents (conductance matrix) needed for discretizing eddy current problems over hexahedral primal grids by means of the Finite Integration Technique (FIT) and the Cell Method (CM). We prove that, unlike the mass matrices of Finite Elements, the proposed matrices ensure both the stability and the consistency of the discrete equations introduced in FIT and CM. More >

C. K. Au¹

CMES-Computer Modeling in Engineering & Sciences, Vol.29, No.3, pp. 151-162, 2008, DOI:10.3970/cmes.2008.029.151

Abstract Ribbons may be used for the modeling of DNAs and proteins. The topology of a ribbon can be described by the linking number, while its geometry is represented by the writhe and the twist. These quantities are integrals and are related by the Cǎlugǎreanu's theorem from knot theory. This theorem also describes the relationship between the various conformations. The heart of the Cǎlugǎreanu's theorem rests in the Gauss Integral. Due to the large number of molecules, the topology and the geometry of a ribbon model can be very complicated. As a result, these integrals are commonly evaluated by numerical methods.… More >

D. Kourounis¹, L.N. Gergidis¹, A. Charalambopoulos¹

CMES-Computer Modeling in Engineering & Sciences, Vol.28, No.3, pp. 185-202, 2008, DOI:10.3970/cmes.2008.028.185

Abstract The sensitivity of analytical solutions of the direct acoustic scattering problem in prolate spheroidal geometry on the wavenumber and shape, is extensively investigated in this work. Using the well known Vekua transformation and the complete set of radiating "outwards'' eigensolutions of the Helmholtz equation, introduced in our previous work ([Charalambopoulos and Dassios(2002)], [Gergidis, Kourounis, Mavratzas, and Charalambopoulos (2007)]), the scattered field is expanded in terms of it, detouring so the standard spheroidal wave functions along with their inherent numerical deficiencies. An approach is employed for the determination of the expansion coefficients, which is optimal in the sense, that minimizes the… More >

X.Y. Cui^1,2, G. R. Liu^2,3, G. Y. Li¹, X. Zhao², T.T. Nguyen², G.Y. Sun¹

CMES-Computer Modeling in Engineering & Sciences, Vol.28, No.2, pp. 109-126, 2008, DOI:10.3970/cmes.2008.028.109

Abstract A smoothed finite element method (SFEM) is presented to analyze linear and geometrically nonlinear problems of plates and shells using bilinear quadrilateral elements. The formulation is based on the first order shear deformation theory. In the present SFEM, the elements are further divided into smoothing cells to perform strain smoothing operation, and the strain energy in each smoothing cell is expressed as an explicit form of the smoothed strain. The effect of the number of divisions of smoothing cells in elements is investigated in detail. It is found that using three smoothing cells for bending strain energy integration and one… More >