W. Wei, David CC LAM¹

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.3&4, pp. 235-246, 2011, DOI:10.3970/cmes.2011.075.235

Abstract Chain rotations in macromolecular solids are constrained by entanglements. The effects of constraints on strain deformation and strain gradient deformation were investigated using molecular dynamic (MD) simulation in this paper. The effects on the chains were examined by embedding the chains inside bent beams. For thick beams, the simulated elastic moduli for styrene butyl rubber (SBR), polyimide (PI) and polyethylene (PE) were in good agreement with elastic moduli reported in the literature. The elastic moduli varied linearly with entanglements and inversely with the molecular weight. For thin beams where strain gradients were non-negligible, the results More >

Canan Köroğlu¹, Turgut Öziş²

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.3&4, pp. 223-234, 2011, DOI:10.3970/cmes.2011.075.223

Abstract He's parameter-expanding method with an adjustment of restoring forces in terms of Chebyshev's series is used to construct approximate frequency-amplitude relations for a conservative nonlinear singular oscillator in which the restoring force is inversely proportional to the dependent variable or in form of rational function of dependant variable. The procedure is used to solve the nonlinear differential equation approximately. The approximate frequency obtained using this procedure is more accurate than those obtained using other approximate methods and the discrepancy between the approximate frequency and the exact one negligible. More >

Zai You Yan¹, Qiang Zhang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.3&4, pp. 205-222, 2011, DOI:10.3970/cmes.2011.075.205

Abstract In a boundary element method, the treatment of all the possible singular integrals is very important for the correctness and accuracy of the solutions. Generally, the directional derivative of a weakly singular integral is computed by an integral in the sense of Cauchy principal value if the directional derivative of the weakly singular integral kernel is strongly singular or in the sense of Hadamard finite part integral if it is hypersingular. In this paper, we try to discover how the strongly singular and hypersingular integrals are generated and propose an idea to avoid the appearance More >

Nizami Gasilov¹, Şahin Emrah Amrahov², Afet Golayoğlu Fatullayev¹, Halil İbrahim Karakaş¹, Ömer Akın³

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.3&4, pp. 189-204, 2011, DOI:10.3970/cmes.2011.075.189

Abstract In this paper, linear systems with a crisp real coefficient matrix and with a vector of fuzzy triangular numbers on the right-hand side are studied. A new method, which is based on the geometric representations of linear transformations, is proposed to find solutions. The method uses the fact that a vector of fuzzy triangular numbers forms a rectangular prism in n-dimensional space and that the image of a parallelepiped is also a parallelepiped under a linear transformation. The suggested method clarifies why in general case different approaches do not generate solutions as fuzzy numbers. It… More >

Peng Weihong¹, Cao Guohua², Dongzhengzhu¹, Li Shuncai³

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.3&4, pp. 173-188, 2011, DOI:10.3970/cmes.2011.075.173

Abstract Numerical method is applied to investigate the Darcy-Stokes equations, which is governing the steady incompressible Stokes flow past a circular cavity in a porous medium. The free fluid flow is modeled by the incompressible Stokes equations, and the flow in the porous medium is imposed by Darcy equations. Based on domain decomposition method with D-N alternating iteration algorithm, the coupling method of finite difference method and natural boundary element method is studied for the coupling Darcy-Stokes equations under a certain pressure difference. The numerical results indicate that the finite difference and natural boundary element coupling More >

Kazuhiko Suga^1,2, Takahiko Ito¹

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.2, pp. 141-172, 2011, DOI:10.3970/cmes.2011.075.141

Abstract The multiple-relaxation-time lattice Boltzmann method for micro-scale flows (MRT µ-flow LBM) is extensively evaluated in this study. Following the study of Chai, Shi, Guo and Lu (2010), the diffusive bounce-back wall boundary condition and the collision matrix are modeled. To determine the model parameters, the first-order, 1.5-order and second-order slip-flow models are discussed. Since the mean free path of gas molecules is considered to be influenced by the wall in micro flow systems, the effects of a correction function after Stops (1970) are also evaluated. As the increase of the Knudsen number (Kn), it is… More >

L.Q. Moreira¹, F.P. Mariano², A. Silveira-Neto¹

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.2, pp. 113-140, 2011, DOI:10.3970/cmes.2011.075.113

Abstract Turbulence in fluid flow is one of the most challenging problems in classical physics. It is a very important research problem because of its numerous implications, such as industrial applications that involve processes using mixtures of components, heat transfer and lubrication and injection of fuel into the combustion chambers and propulsion systems of airplanes. Turbulence in flow presents characteristics that are fully nonlinear and that occur at high Reynolds numbers. Because of the nonlinear nature of turbulent flow, an increase in the Reynolds number implies an increase in the Kolmogorov wave numbers, and the flow… More >

B.-H. Lee¹, J.-C. Park², M.-H. Kim³, S.-C. Hwang²

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.2, pp. 89-112, 2011, DOI:10.3970/cmes.2011.075.089

Abstract The violent free-surface motions and the corresponding impact loads are numerically simulated by using the refined Moving Particle Simulation (MPS) method, which was originally proposed by Koshizuka and Oka (1996) for incompressible flows. In the present method, accuracy and efficiency are significantly improved compared to the original MPS method by using optimal source term, optimal gradient and collision models, and improved solid-boundary treatment and search of free-surface particles. The refined MPS method was verified through comparisons against Kishev et al.'s (2006) sloshing experiment. It is also demonstrated that the refined MPS method is excellent in More >

Mohsen Sadeghbeigi Olyaie¹, Mohammad Reza Razfar², Edward J. Kansa³

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.1, pp. 43-88, 2011, DOI:10.3970/cmes.2011.075.043

Abstract This paper presents integration of reliability analysis with topology optimization design for a linear mircroactuator, including multitude cantilever piezoelectric bimorphs. Each microbimoph in the mechanism can be actuated in both axial and flexural modes simultaneously. We consider quasi-static and linear conditions, and the smoothed finite element method (S-FEM) is employed in the analysis of piezoelectric effects. Since microfabrication methods are used for manufacturing this type of actuator, uncertainty variables become very important. Hence, these variables are considered as constraints during our topology optimization design process and reliability based topology optimization (RBTO) is conducted. To avoid… More >

Ali Bekir Yildiz¹

CMES-Computer Modeling in Engineering & Sciences, Vol.75, No.1, pp. 33-42, 2011, DOI:10.3970/cmes.2011.075.033

Abstract The generalized method for determination of time constants of linear circuits is introduced. Nodal and mesh analysis, conventional methods whose applications are simpler than the state-space formulation, are used in obtaining the system equations. The approach is based on the use of the relationship between transfer functions and system equations of linear circuits, obtained by the conventional methods. The examples of active and passive circuits are given to illustrate the method. More >