W. A. El-Askary¹

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.3&4, pp. 203-232, 2011, DOI:10.3970/cmes.2011.074.203

Abstract Large eddy simulation (LES) is a viable and powerful tool to analyze unsteady three- dimensional turbulent flows. In this paper, the method of LES is used to compute a plane turbulent supersonic boundary layer subjected to different pressure gradients. The pressure gradients are generated by allowing the flow to pass in the vicinity of an expansion-compression ramp (inclined backward-facing step with leeward-face angle of 25 degrees) for an upstream Mach number of 2.9. The inflow boundary condition is the main problem for all turbulent wall-bounded flows. An approach to solve this problem is to extract instantaneous velocities, temperature and density… More >

Xiaowei Zeng¹

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.3&4, pp. 183-202, 2011, DOI:10.3970/cmes.2011.074.183

Abstract This paper presents an atomistic field theory and its application in modeling and simulation of nano/micro materials. Atomistic formulation and finite element implementation of the atomistic field theory is briefly introduced. Numerical simulations based on the field theory are performed to investigate the material behaviors of bcc iron at coarse-grained scale and we have obtained the mechanical strength and elastic modulus, which are in good agreement with results by first principles calculations. Also the nanoscale deformation and failure mechanism are revealed in bcc iron nanorods under simple tension. It is interesting to observe that under tensile loading, iron has gone… More >

Zhen Yang¹, Xingsheng Gu², Xiaoyi Liang^1,3

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.3&4, pp. 161-182, 2011, DOI:10.3970/cmes.2011.074.161

Abstract Mesoporous carbons are synthesized by organic-organic self-assembly of triblock copolymer F127 and a new type of carbon precursor as resorcinol-furfural oligomers. Some factors will impact the mesoporous carbons pore structure and properties were studied. The main factors, such as the ratio of triblock copolymer F127 and oligomers, degree of polymerizstry of resorcinol-furfural oligomers, the ratio of resorcinol-furfural oligomers - F/R, and their mutual relations were identified. Aimed at balancing the complex characteristic of mesoporous structure and adsorption properties, a classification and optimization model based on support vector machine is developed. The optimal operation conditions of Barret-Joyner-Halenda (BJH) adsorption cumulative volume… More >

Xiao Zhao¹, Haitian Yang^1,2, Qiang Gao¹

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.2, pp. 139-160, 2011, DOI:10.3970/cmes.2011.074.139

Abstract A piecewised adaptive algorithm in the time domain is presented to solve the transient convection-diffusion heat transfer problem. By expanding all variables at a time interval, an initial and boundary value problem is decoupled into a series of recursive boundary value problems which can be solved by FEM or other well developed numerical schemes to deal with boundary value problems. A steady computing accuracy can be adaptively maintained via the power increase of the expansion, particularly when the step size varies in the whole computing process. Additionally for the nonlinear cases, there is no requirement of iteration and additional assumption… More >

Yi W. Wan¹, Huan J. Keh²

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.2, pp. 109-138, 2011, DOI:10.3970/cmes.2011.074.109

Abstract The steady rotation of an axially symmetric particle about its axis of revolution normal to two plane walls at an arbitrary position between them in a viscous fluid is studied theoretically in the limit of small Reynolds number. The fluid is allowed to slip at the surface of the particle. A method of distribution of a set of spherical singularities along the axis of revolution inside a prolate particle or on the fundamental disk within an oblate particle is used to find the general solution for the fluid velocity distribution that satisfies the boundary conditions at the confining walls and… More >

Gongsheng Li¹, De Yao², Hengyi Jiang³, Xianzheng Jia¹

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.2, pp. 83-108, 2011, DOI:10.3970/cmes.2011.074.083

Abstract This paper deals with an inverse problem of determining a time-depen -dent reaction coefficient arising from a disturbed soil-column infiltrating experiment based on measured breakthrough data. A purpose of doing such experiment is to simulate and study transport behaviors of contaminants when they vertically penetrating through the soils. Data compatibility of the inverse problem is discussed showing a sufficient condition to the solution's monotonicity and positivity with the help of an adjoint problem. Furthermore, an optimal perturbation regularization algorithm is applied to solve the inverse problem, and two typical numerical examples are presented to support the inversion algorithm. Finally, transport… More >

C. Jiang^1,2, Q.F. Zhang¹, X. Han¹, D. Li³, J. Liu¹

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.1, pp. 65-82, 2011, DOI:10.3970/cmes.2011.074.065

Abstract In this paper, an interval optimization method is developed to deal with a class of problems that there exists dependence between the interval parameters. An ellipsoidal convex model is used to model the uncertainty domain, in which the parameter dependence can be well reflected through the shape of a multi-dimensional ellipsoid. Based on an order relation and a reliability-based possibility degree of interval, the uncertain optimization can be transformed to a deterministic nesting optimization. An efficient algorithm is then constructed to solve the created nesting optimization, in which a sequence of approximate interval optimizations are created and the optimal design… More >

Fangyi Li^1,2, Zhen Luo³, Guangyong Sun⁴

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.1, pp. 39-64, 2011, DOI:10.3970/cmes.2011.074.039

Abstract This paper studies the reliability-based multiobjective optimization by using a new interval strategy to model uncertain parameters. A new satisfaction degree of interval, which is significantly extended from [0, 1] to [–∞, +∞], is introduced into the non-probabilistic reliability-based optimization. Based on a predefined satisfaction degree level, the uncertain constraints can be effectively transformed into deterministic ones. The interval number programming method is applied to change each uncertain objective function to a deterministic two-objective optimization. So in this way the uncertain multiobjective optimization problem is transformed into a deterministic optimization problem and a reliability-based multiobjective optimization is then established. For… More >

E. Schnack¹, W. Weber², Y. Zhu³

CMES-Computer Modeling in Engineering & Sciences, Vol.74, No.1, pp. 1-38, 2011, DOI:10.3970/cmes.2011.074.001

Abstract Three dimensional fracture mechanics was done by several groups in the past. One topic for these three dimensional fracture mechanics is to consider re-entrant corners or wedges for isotropic material. An algorithm was developed in the past to compute the dominant eigenvalues for those problems with high accuracy. Based on Kondratiev's Lemma for elliptic boundary value problems it is started with the asymptotic for the displacement and stress distribution around these three dimensional corners. By considering the mixed boundary value problem, the field quantities in the vicinity of corner points are computed by using a special finite element formulation, which… More >

Chein-Shan Liu¹, Satya N. Atluri²

CMES-Computer Modeling in Engineering & Sciences, Vol.73, No.4, pp. 395-432, 2011, DOI:10.3970/cmes.2011.073.395

Abstract In this paper we solve a system of nonlinear algebraic equations (NAEs) of a vector-form: F(x) = 0. Based-on an invariant manifold defined in the space of (x,t) in terms of the residual-norm of the vector F(x), we derive a system of nonlinear ordinary differential equations (ODEs) with a fictitious time-like variable t as an independent variable: x^· = λ[αF + (1−α)B^TF], where λ and α are scalars and B_ij = ∂F_i/∂x_j. From this set of nonlinear ODEs, we derive a purely iterative algorithm for finding the solution vector x, without having to invert the Jacobian (tangent stiffness matrix)… More >