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 compare favourably with those obtained… More >

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 nanocomposites; and finally discusses prospects… More >

Shueei-Muh Lin¹, Sen-Yung Lee², Yu-Sheng Lin³

CMES-Computer Modeling in Engineering & Sciences, Vol.23, No.3, pp. 175-186, 2008, DOI:10.3970/cmes.2008.023.175

Abstract The blade of a horizontal-axis wind power turbine is modeled as a rotating beam with pre-cone angles and setting angles. Based on the Bernoulli-Euler beam theory, without considering the axial extension deformation and the Coriolis forces effect, the governing differential equations for the bending vibration of the beam are derived. It is pointed out that if the geometric and the material properties of the beam are in polynomial forms, then the exact solution for the system can be obtained. Based on the frequency relations as revealed, without tedious numerical analysis, one can reach many general qualitative conclusions between the natural… More >

A.P.S. Selvadurai¹, H. Ghiabi²

CMES-Computer Modeling in Engineering & Sciences, Vol.23, No.1, pp. 53-74, 2008, DOI:10.3970/cmes.2008.023.053

Abstract This paper deals with the problem of the consolidation of a composite consisting of alternate layers of soft clay and a granular material. A series of experiments were conducted on components to develop the constitutive models that can be implemented in a computational approach. The constitutive response of the soft clay is represented by a poro-elasto-plastic Cam clay-based model and the granular medium by an elasto-plastic model with a Drucker-Prager type failure criterion and a non-associated flow rule. The computational poro-elasto-plastic model is used to calibrate the experimental results derived from the one-dimensional tests and to establish the influence of… More >

Ya Yan Lu¹, Jianxin Zhu²

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.3, pp. 235-248, 2007, DOI:10.3970/cmes.2007.022.235

Abstract The perfectly matched layer (PML) is a widely used technique for truncating unbounded domains in numerical simulations of wave propagation problems. In this paper, the PML technique is used with a standard one-way model to solve a benchmark problem for underwater acoustics modeling. Accurate solutions are obtained with a PML layer with a thickness of only a quarter of the wavelength. The effect of a PML is analyzed in a perturbation analysis for waveguides. More >

Shamsh Tabrez, Mira Mitra, S. Gopalakrishnan¹

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.1, pp. 77-90, 2007, DOI:10.3970/cmes.2007.022.077

Abstract In this paper, wave propagation is studied in degraded composite beam due to moisture absorption. The obtained wave responses are then used for diagnosis of the degraded zone. Moisture absorption causes an irreversible hygrothermal deterioration of the material. The change in temperature and moisture absorption changes the mechanical properties. Thus this affects the structure in dimensional stability as well as material degradation due to reduction in mechanical properties. Here, the composite beam is modeled as Timoshenko beam using wavelet based spectral finite element (WSFE) method. The WSFE technique is especially tailored for simulation of wave propagation. It involves Daubechies scaling… More >

L.N. Gergidis, D. Kourounis, S. Mavratzas, A. Charalambopoulos¹

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.2, pp. 157-176, 2007, DOI:10.3970/cmes.2007.021.157

Abstract A new complete set of scattering eigensolutions of Helmholtz equation in spheroidal geometry is constructed in this paper. It is based on the extension to exterior boundary value problems of the well known Vekua transformation pair, which connects the kernels of Laplace and Helmholtz operators. The derivation of this set is purely analytic. It avoids the implication of the spheroidal wave functions along with their accompanying numerical deficiencies. Using this novel set of eigensolutions, we solve the acoustic scattering problem from a soft acoustic spheroidal scatterer, by expanding the scattered field in terms of it. Two approaches concerning the determination… More >

Anuj Pratap Singh, V. Mani, Ranjan Ganguli¹

CMES-Computer Modeling in Engineering & Sciences, Vol.21, No.2, pp. 133-148, 2007, DOI:10.3970/cmes.2007.021.133

Abstract This paper investigates the use of Genetic Programming (GP) to create an approximate model for the non-linear relationship between flexural stiffness, length, mass per unit length and rotation speed associated with rotating beams and their natural frequencies. GP, a relatively new form of artificial intelligence, is derived from the Darwinian concept of evolution and genetics and it creates computer programs to solve problems by manipulating their tree structures. GP predicts the size and structural complexity of the empirical model by minimizing the mean square error at the specified points of input-output relationship dataset. This dataset is generated using a finite… More >

S. Sabchevski¹, I. Zhelyazkov², M. Thumm³, S. Illy⁴, B. Piosczyk⁵, T.-M. Tran^6,7, J. Gr. Pagonakis⁸

CMES-Computer Modeling in Engineering & Sciences, Vol.20, No.3, pp. 203-220, 2007, DOI:10.3970/cmes.2007.020.203

Abstract Computer aided design of powerful gyrotrons for electron cyclotron resonance heating and current drive of fusion plasmas requires adequate physical models and efficient software packages for analysis, comparison and optimization of their electron-optical systems through numerical experiments. In this paper, we present and discuss the current status of the simulation tools available to the researchers involved in the development of multi-megawatt gyrotrons for the ITER project, review some of their recent upgrades and formulate directions for further modifications and improvements. Illustrative examples used represent results from recent numerical investigations of real constructions. Some physical problems that are outside of the… More >

T.C. Theodosiou¹, D.A. Saravanos²

CMES-Computer Modeling in Engineering & Sciences, Vol.19, No.2, pp. 121-134, 2007, DOI:10.3970/cmes.2007.019.121

Abstract In this paper a new method is introduced for carbon nanotube modeling combining features of Molecular Mechanics and Finite Element Analysis. Repetitive atomic cells are treated as finite elements, whose internal energy is determined by the semi-empirical Brenner molecular potential model; internal forces and linearized stiffness matrices are formulated analytically in order to gain in speed and accuracy, and the resultant discrete system is formulated and solved using the Newton-Raphson method. The presented method is validated through comparisons to numerical and experimental results provided by other researchers. The bending and shearing of CNTs is also simulated. More >