G.V. Norton^*, J.C. Novarini^†

Molecular & Cellular Biomechanics, Vol.4, No.2, pp. 75-86, 2007, DOI:10.3970/mcb.2007.004.075

Abstract Ultrasonic imaging in medical applications involves propagation and scattering of acoustic waves within and by biological tissues that are intrinsically dispersive. Analytical approaches for modeling propagation and scattering in inhomogeneous media are difficult and often require extremely simplifying approximations in order to achieve a solution. To avoid such approximations, the direct numerical solution of the wave equation via the method of finite differences offers the most direct tool, which takes into account diffraction and refraction. It also allows for detailed modeling of the real anatomic structure and combination/layering of tissues. In all cases the correct… 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 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. 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… 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 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 More >

Shunde Yin¹, Leo Rothenburg¹, Maurice B. Dusseault¹

CMES-Computer Modeling in Engineering & Sciences, Vol.19, No.2, pp. 111-120, 2007, DOI:10.3970/cmes.2007.019.111

Abstract Subsidence problem is of great importance in petroleum engineering and environmental engineering. In this paper, we firstly apply a hybrid Displacement Discontinuity-FEM modeling to this classic problem: the evaluation of subsidence over a compacting oil reservoir. We use displacement discontinuity method to account for the reservoir surrounding area, and finite element methods in the fully coupled simulation of the reservoir itself. This approach greatly reduces the number of degrees of freedom compared to an analyzing fully coupled problem using only a finite element or finite difference discretization. More >

Heng Xie¹, Seiichi Koshizuka², Yoshiaki Oka²

CMES-Computer Modeling in Engineering & Sciences, Vol.18, No.1, pp. 1-16, 2007, DOI:10.3970/cmes.2007.018.001

Abstract A model of a single liquid drop colliding on solid surface is developed based with Moving Particle Semi-implicit (MPS) method. The mathematical model involves gravity, viscosity and surface tension. The wettability between the impact liquid and the solid surface is modeled by the contact angle model and the non-slip boundary condition. The particles of the drop are divided into four types in which the model varies to simulate the liquid particles in different area. The model is validated by the comparison of the theoretical results. The complete dynamic process including the spreading, the recoiling, re-bouncing More >

Joseph G. Lawrence, John P. Dismukes, Arunan Nadarajah¹

FDMP-Fluid Dynamics & Materials Processing, Vol.3, No.3, pp. 255-264, 2007, DOI:10.3970/fdmp.2007.003.255

Abstract The atmospheric chemical vapor deposition process on continuous glass sheets is a well developed one and the parameters that affect it are relatively well understood. When this process is converted to coat discrete glass plates it introduces a new variable, the gap between the glass plates, which can significantly impact the quality of the coatings. In this study a 2D pseudo steady state model of the process was developed to study the effect of the gap, and the ratio of outlet to inlet gas flow rates (called the bias), on the coating quality. The model… More >