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25 July 2007, Volume 24 Issue 4 Previous Issue    Next Issue

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Numerical Methods for Energy Flux of Temperature Diffusion Equation on Unstructured Grids LÜ Guixia, SHEN Longjun, SHEN Zhijun 2007, 24(4): 379-386.  Abstract ( )   PDF (380KB) ( )   Numerical methods for energy flux of temperature diffusion equation on unstructured grids are discussed.A finite point method(FPM) is used to get numerical formulae of energy flux based on two-point formula or three-point formula of FPM.These formulae are applicable to unstructured grids,such as arbitrary polygon and unmatched grids etc..A numerical formula is given to compute tem-peratures at grid nodes.Numerical experiments show that the discrete solutions based on two-point formula and three-point formula have second-order convergence rate even if grids distort heavily.Accuracy of the discrete solutions based on three-point formula is better than that of two-point formula.

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Scalability Analysis for Parallel Algebraic Multigrid Algorithms XU Xiaowen, MO Zeyao 2007, 24(4): 387-394.  Abstract ( )   PDF (507KB) ( )   We analyze scalability of parallel algebraic multigrid algorithms for large sparse linear systems.To analyze performance of the parallel iterative algorithm and its implementation,a method for analyzing scalability of parallel computing is presented. Numerical results show that the average stencil size of the grid operator and the convergence efficiency are keys in the parallel algebraic multigrid method.

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A Eulerian Approach Based on CE/SE Method for 2D Multimaterial Elastic-Plastic Flows WANG Jingtao, ZHANG Deliang, LIU Kaixin 2007, 24(4): 395-401.  Abstract ( )   PDF (409KB) ( )   We extend the CE/SE scheme and present a complete Eulerian approach for two-dimensional(plane strain and axisymmetry) elastic-plastic flows with solid features.Eulerian governing equations are adopted and solved on a fixed Cartesian grid.Johnson-Cook constituted equations and Mie-Grüneisen equation of state are used to describe materials.A hybrid particle level set method is used to trace interfaces of materials.Two types of boundary condition are presented in tracking interface.The penetration of a steel target by a WHA long rod is simulated and the computational results are carefully compared with those in other literatures.

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Hourglass Control in Finite Element Code CHENG Junxia 2007, 24(4): 402-406.  Abstract ( )   PDF (292KB) ( )   We analyze unphysical grid distortion caused by one-point quadrature in 4-node isoparametric finite element computer program.It is concluded that the rank deficiency of stiffness matrix results in hourglass distortion.A method that controlls hourglass distortion by eliminating rank deficiency is developed and validated by patch tests.

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Wall Heating and Q&H Method in Arbitrary n-polygon Lagrange Grids Finite Volume Method WANG Ruili, LIN Zhong, WEI Lan, GE Quanwen 2007, 24(4): 407-412.  Abstract ( )   PDF (398KB) ( )   Based on Noh's artificial viscosity with artificial heat flux method(Q & H),we present a Q & H scheme on arbitrary n-polygon meshes.Noh's Q & H on structured meshes is extended to unstructured meshes in two dimensions.Numerical results of Noh's problem and collision of two metals show that the Q&H method on unstructured meshes eliminates wall heating effectivly.

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Small Correlation Time Colored Noise Method for Two-phase Turbulent Flows and Simulation of Wall-jet-flow LI Zhaoxiang, XU Jiangrong, YANG Zhonghua 2007, 24(4): 413-418.  Abstract ( )   PDF (352KB) ( )   Based on a colored noise model with general Gaussian process,by functional derivation and small correlation time expansion,high-dimensional colored noises are calculated approximately and an effective Fokker-Planck equation(FPE) is derived.The effective FPE is applied to obtain probability density function transport equations of particles in two-phase flows and a second order moment model of two-phase flows.It is simplified into an algebra stress model(ASM).The finite analytic numerical method used in convective diffusion equation is applied to the second-order moment model.A wall-jet-flow loaded with solid particles is calculated with ASM and finite analytic numerical method.Numerical results are compared with experimental results.

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Computation of Non-Darcy Flow with Hybrid Grids HUANG Feng, LU Detang 2007, 24(4): 419-425.  Abstract ( )   PDF (365KB) ( )   For low non-Darcy flow in vertically fractured wells,based on the generalized Darcy's law,a series of non-Darcy flow differential equations and definite conditions of vertical fractured wells are built up.We assume that the stratum and fluid are slightly compressible and the outer edge is circular.Hybrid grids of regular and PEBI grids are used to divide solution domains.Numerical solution of bottomhole pressure is obtained with finite difference method.The bottomhole pressure and its derivative with finite conductivity considering the skin and well-bore storage effects are analysed in detail.The numerical solution closes to the theoretical result.

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Determination of Dynamic Load Distribution on a Kirchhoff Plate by FEM MA Chenming 2007, 24(4): 426-432.  Abstract ( )   PDF (399KB) ( )   The determination of dynamic load distribution on a Kirchhoff plate by FEM is studied,which is an inverse problem. To determine the load distribution,we select strain values on the surface of the plate as additional information.Numerical Laplace transformation and inversion are employed to study dynamic behavior of the problem.The linear controlling system,derived from strain-deformation relation in Kirchhoff plate theory,is ill-conditioned.Tikhonov regularization and L-curve method are employed.Numerical examples indicate that the inverse strategy is efficient.

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A Fast Multiple Boundary Element Method for Two-dimensional Electrostatic Field with Arbitrary Plane Charge Distribution HE Zeng, LÜ Junchao, DAI Chenghao 2007, 24(4): 433-438.  Abstract ( )   PDF (307KB) ( )   Based on the initial FMM,an FMM algorithm is proposed to solve electrostatic field problem.The algorithm introduces diagonalization to reduce time in forming local spread coefficient and enhance the computing efficiency.The computing speed and high precision of the algorithm in dealing with large-scale issue are shown with numerical examples.

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Fast Domain Decomposition Method for Finite Periodic Electromagnetic Structures AN Xiang, LÜ Zhiqing 2007, 24(4): 439-444.  Abstract ( )   PDF (382KB) ( )   A highly efficient domain decomposition method based on finite element tearing and interconnecting algorithm is presented for analysis of finite periodic electromagnetic structures.The original domain is partitioned into several nonoverlapping subdomains to decrease computational scale and complexity.The general variational principle is employed in communicating information between subdomains with Lagrange multipliers,which yields a reduced-order coarse problem.To improve scalability of the algorithm,basic subdomains are introduced.The results show that the method is highly efficient and scalable even on a sequential computational platform.Compared with traditional methods,the proposed method is more efficient,especially for the problems with geometric repetitions,such as photonic crystals.

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MLFMA in Fast Computation of EM Scattering by a Three-dimensional Electrically Large Complex Cavity LUO Wei, GAO Zhengping, ZHANG Huaiwu 2007, 24(4): 445-451.  Abstract ( )   PDF (378KB) ( )   An iterative physical optics(IPO) method combined with multilevel fast multipole algorithm(MLFMA) is used to solve electromagnetic scattering by a three-dimensional complex cavity efficiently and rapidly.The iterative formulations of hybrid algorithm are derived.For slow bending cavities in engineering,a proper subsection structured grouping method is provided to avoid the shelter of facets between two groups.A generalized reciprocity integral(GRI) method is applied to cavities with complex termination.The methods obtain accurate results and improve computing speed.

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An FDTD Model of Photonic Crystal Laser with Four-energy-level Gain Media WANG Hong, OUYANG Zhengbiao, HAN Yanling, MENG Qingsheng 2007, 24(4): 452-456.  Abstract ( )   PDF (314KB) ( )   A model of one-dimensional photonic crystal laser with four-energy-level gain media is presented.The model consists of Maxwell-Bloch equations coupled with rate equations of electronic population in a photonic crystal laser system.The discretization of coupled equations is accomplished with finite different time domain(FDTD).Spectra,lasing mode,lasing threshold and dynamics of the photonic crystal laser are obtained.The simulation shows good agreement with theoretical predictions.

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Monte Carlo Simulation of Light Multiple Scattering in Polymers MA Changqun, TANG Zhenfang, ZHANG Jie, YE Qin 2007, 24(4): 457-462.  Abstract ( )   PDF (517KB) ( )   A mathematical model for multiple scattering of light conducted in polymers is presented.Based on the Mie scattering theory,Monte Carlo method is employed and a program is developed.By simulating scattering of a photon,we simulate problem with light source as laser or CCFL.Distribution of light out of source in polymers is obtained by statistic calculation.The results show that a plane light in polymer can be obtained with body scattering principle and intensity distribution of light escaping from polymer can be well controlled.

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A Nonequilibrium Molecular Dynamics Method for Thermal Conductivity Simulation CAO Bingyang 2007, 24(4): 463-466.  Abstract ( )   PDF (268KB) ( )   A nonequilibrium molecular dynamics(NEMD) method based on construction of uniform internal heat source for simulating thermal conductivity is put forward.The method holds energy and momentum conservations and shows rapid convergence comparable to the reversed NEMD(RNEMD) method.It overcomes the local thermodynamic nonequilibrium problem of hot/cold source regimes in traditional NEMD schemes.Compared with the RNEMD method,the method may cause smaller temperature difference and density inhomogeneity in the simulated molecule system.The method is used to simulate thermal conductivity of liquid argon and is compared with the RNEMD method.

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TE & TM Waves in Four Sensing Waveguides with Non-rectangular Cross Section WEI Yiming 2007, 24(4): 467-474.  Abstract ( )   PDF (390KB) ( )   Sensing waveguides with non-rectangular cross-section are transformed to rectangular ones by means of conformal mapping.The electric field,magnetic field,critical frequency,surface current, power transmission and attenuation,as well as TE and TM modes in waveguides are discussed.Numerical results of four sensing waveguides with non-rectangular cross-section are given.

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Dielectric Characteristic and Optical Absorption of Composite Media:Graded Spherical Particles XIE Bingchuan, SHEN Tinggen, WU Yamin, HE Qin 2007, 24(4): 475-479.  Abstract ( )   PDF (276KB) ( )   We apply effective dipole approximation to investigate the equivalent dielectric constant of inclusion and the effective response and optical absorption in composites media of metal spherical particles.The dielectric constant varies along the radius of the particles.εe exhibits a monotonic decrease with the power index n while the dielectric constant shows a power law gradation.The presence of the gradation in metal particles yields a resonant optical absorption peak.It shows red-shift with mω and mν of the metal-dielectric composites.

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DFT Study on Structure and Stability of GanNm+(n=1~8,m=1~2) Clusters LI Enling, MA Hong, CHEN Guican, WANG xuewen 2007, 24(4): 480-486.  Abstract ( )   PDF (440KB) ( )   The B3LYP method of density functional theory(DFT) is used to optimize geometry configuration,stability and frequency calculation of GanN+(n=2~8) and GanN2+(n=1~7) cation clusters at the level of 6-31G*.Ground state of GanN+(n=2~8) and GanN2+(n=1~7) clusters are obtained.The geometry of clusters transforms from a planar structure to a spacial structure as cluster sizes of GanN+(n=2~8) and GanN2+(n=1~7) are increased to 6 and 7,respectively.Among GanN+(n=2~8) and GanN2+(n=1~7) cation clusters,Ga4N+,Ga6N+,Ga3N2+ and Ga5N2+ are stabler.

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Hydrogen-like Wave Functions in a Non-relativistic Average Atom Model for Plasmas GUO Yonghui, DUAN Yaoyong, KUAI Bin 2007, 24(4): 487-493.  Abstract ( )   PDF (357KB) ( )   Equations in a non-relativistic average atom model for plasmas are solved.Numerical techniques,global chart and code design are given in detail.Semi-analytical results obtained by variational method and test-potential method are compared with those by full numerical method in the same model and those in different physical models.Advantages and limitations of the model and algorithm are pointed out.

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Digital Stream Encrypt Based on SCS-PRBG WANG Xingyuan, LIU Wei, LI Ruijuan 2007, 24(4): 494-498.  Abstract ( )   PDF (413KB) ( )   Regarding to degeneration of dynamics characteristics in a traditional single chaotic system,we propose a switch controller chaos pseudo random bit generator(SCS-PRBG) based on multiple chaotic systems and switch control.Theoretic analysis of random key stream and its performance show that the key stream has better randomicity and security.With parallel computation,the speed of encryption is improved. The expriment indicates better security of this algorithm.

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Effects of Limited Velocity on Traffic Flow YANG Xianqing, ZHANG Wei, QIU Kang, SUN Dapeng, ZHAO Yuemin 2007, 24(4): 499-504.  Abstract ( )   PDF (503KB) ( )   Effect of limited velocity on traffic flow is studied with cellular automaton.The simulation indicates that a saturated traffic flow determined by limited speed exists.The limited velocity results in various phase separations.In a fixed model,as the car density is low,two free-flow phases occur.As the density is high,a separation of maximum traffic flow phase from a free flow phase is observed.In an random model,as the density is high,a maximum flow-jamming-free flow appears.The traffic flow and critical density are given.