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25 May 2007, Volume 24 Issue 3 Previous Issue    Next Issue

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An Advancing Reference Jacobian Optimization-based Grid Rezone Method YAO Yanzhong, YUAN Guangwei, NI Guoxi 2007, 24(3): 253-260.  Abstract ( )   PDF (736KB) ( )   Combining reference Jacobian method(RJM) with advancing-front method,we present a strategy named advancing reference Jacobian method(ARJM).It advances the optimization process step by step from one part of the computational region boundary to the remaining parts.In each step,two neighboring rows(or columns) are taken as the boundaries of the sub-region and the rear row(column) nodes are the optimized ones and the middle row(or column) is optimized by RJM. Analyses and numerical experiments show that the ARJM is much faster than RJM.The geometric qualities of rezoned grids by ARJM are equal to or even better than those by RJM.The rezoned grids obtained by ARJM are closer to Lagrangian grids than those by RJM.

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An Arbitrary Lagrangian-Eulerian Method with Adaptive Moving Mesh WANG Yongjian, ZHAO Ning, MAO Junfeng, WANG Donghong 2007, 24(3): 261-267.  Abstract ( )   PDF (405KB) ( )   A finite volume scheme is developed for Lagrangian equations in hydrodynamics.With ENO(essentially non-oscillatory) interpolating polynomials on structure grids,a high accurate finite volume scheme is constructed by modifying a first order finite volume scheme on rectangular meshes.Numerical experiments are made with an adaptive moving mesh and arbitrary Lagrangian-Eulerian method.It shows effectiveness of the method.

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Assistant Mesh Difference Method for Parabolic Equations on Distorted Meshes with Large Aspect Ratio HANG Xudeng, LI Jinghong, YUAN Guangwei 2007, 24(3): 268-276.  Abstract ( )   PDF (649KB) ( )   Construction of difference schemes for parabolic equations on distorted meshes with large aspect ratio is discussed.The limitation of 9-point scheme is provided.An assistant mesh difference method is proposed for distorted meshes with large aspect ratio to improve precision and efficiency.Based on the conservation law,applying appropriate rezone methods for meshes we modify the 9-point method to reduce computation error due to poor regularity of the meshes and low precision due to the approximation to vertices values by an average of neighboring cell values.The nonlinear system obtained is a different system from the 9-point scheme.Its solution approximates to the solution with the original meshes.The designed scheme is implemented easily and adapts well to distorted meshes.Numerical experiments show good precision and stability.

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CGNS API and FVM in Unstructured Hybrid Grid Computational Method LEI Guodong, LIU Gongmin, MING Pingjian, ZHANG Wenping, ZHU Minggang 2007, 24(3): 277-281.  Abstract ( )   PDF (365KB) ( )   An unstructured hybrid grid computational method is proposed,in which CGNS API(CFD General Notation System Application Programming Interface) is taken as pre- and post-processing and FVM(Finite Volume Method) is taken as a PDE(Partial Differential Equation) solver.In the pre-processing,the interior mesh faces and boundary mesh faces are indexed with hash table method for the requirment of the FVM solver.The results of the solver are written into original CGNS files with which the post-processing is dealt with by post-processing softwares,such as tecplot,fluent and CFX.For the solver,a cell centered FVM is applied to solve the coupled pressure and velocities with the SIMPLEC(Semi Implicit Method for Pressure Linked Equation Consistent).Two numerical examples are shown.

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Numerical Study of Natural Convection Heat Transfer in a Porous Cavity Under Time-periodic Boundary Conditions WANG Gang, ZENG Min, HUANG Zipeng, WANG Qiuwang 2007, 24(3): 282-286.  Abstract ( )   PDF (274KB) ( )   Unsteady natural convection heat transfer of incompressible fluid in an inclined cavity filled with saturated porous medium is studied numerically.The temperature of the cold sidewall maintains constant and the temperature of the opposite sidewall varies sinusoidally with time.The Brinkman-extended Darcy model and SIMPLER algorithm are adopted.Comprehensive numerical solutions are acquired at a fixed Prandtl number Pr=1 and a Rayleigh number Ra=106.The inclination angle of the enclosure α varies from 0° to 90°.The effects of α and dimensionless oscillation frequency f on the natural convection are analyzed.The maximum heat transfer is reached at f=60π and α=43°.

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Piecewise Parabolic Method for Compressible Multi-fluid Flows with van der Waals Equation of State ZHENG Jianguo, MA Dongjun, SUN Dejun, YIN Xieyuan 2007, 24(3): 287-294.  Abstract ( )   PDF (391KB) ( )   In a compressible fluid-mixture model based on volume fraction, a high-order piecewise parabolic method(PPM) is employed to solve multi-fluid flows characterized by the van der Waals equation of state.A double shock approximation is used in the Riemann solver.Simulation on a pure interface problem indicates that the pressure and velocity profiles do not show any spurious oscillation at the contact discontinuity and the numerical diffusion is limited within two or three cell grids.It shows that the method deals with such physical problems as contact discontinuity,shock, multi-dimensional slip line efficiently.

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Numerical Simulation of Petroleum Reservoir with Anisotropic Permeability LIU Yuetian, XU Mingwang, PENG Daogui, ZHANG Hongwei, DONG Bin 2007, 24(3): 295-300.  Abstract ( )   PDF (333KB) ( )   A model for flow in a 3-dimensional 3-phase anisotropic oil reservoir is established and applied to reservoir development.The model includes a complete anisotropic permeability tensor.It characterizes the anisotropic permeability distribution with different principal directions in different regions.It calculates the fluid flow,the residual oil distribution and the pressure distribution in anisotropic reservoirs accurately.

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Interaction Between Chemical Reactions and Spherically Imploding Detonation Waves CHANG Lina, JIANG Zonglin, QIN Chengsen 2007, 24(3): 301-306.  Abstract ( )   PDF (408KB) ( )   Numerical simulation of spherically imploding detonation waves in hydrogen-oxygen is carried out in an elementary chemical reaction model.Compared with numerical results of imploding shock waves in nitrogen,the discrepancies of gas dynamic characteristics between shock and detonation waves are investigated during implosion.The effect of chemical reactions,combustion and dissociation on detonation waves is revealed.As the wave fronts converge toward the center of symmetry,the front pressures at different radii are almost the same in the two cases.However the front temperatures are different.The temperature increases more rapidly in nitrogen than in hydrogen-oxygen mixture.Higher temperature is reached near the focal point in nitrogen due to its higher dissociation temperature.The energy released at the wave front is negligible in predicting pressure,while it needs to be considered in predicting temperature.

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Natural Difference Method for Groundwater Seepage ZHANG Shifeng, LI Qian, GAO Peiling 2007, 24(3): 307-312.  Abstract ( )   PDF (296KB) ( )   With analysis of water balance in elements controlled by nodes,a stable computational scheme is proposed similar to FEM of Galerkin.It holds mass conservation automatically.A nonlinear phreatic water problem is solved conveniently by this scheme.Numerical calculation provides good result in solving a Theis problem.

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Full-vectorial Analysis of Optical Waveguides with an Improved Finite Difference Method Based on H Fields XIAO Jinbiao, Liu Xu, CAI Chun, FAN Hehong, SUN Xiaohan 2007, 24(3): 313-318.  Abstract ( )   PDF (441KB) ( )   An improved finite difference method in solving vector wave equations based on H fields for full-vectorial analysis of optical waveguides is described.A six-point finite difference scheme of high accuracy is constructed to approximate cross-coupling terms.It takes into account the discontinuities in derivatives of magnetic component at horizontal and vertical interfaces.Moreover,the scheme is independent of structure of waveguide due to explicit expressions.The guided-mode patterns and normalized propagation constants of a step-index fiber,a rectangular waveguide and a rib waveguide are presented.The hybrid nature of full-vectorial guided-modes is demonstrated.The results agree well with analytical solutions and the benchmark results of modal transverse resonance method.It demonstrates accuracy and convergence of the method.

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Structure and Property of (MgB2)n(n=1~3) Clusters:a Density Functional Study CHEN Yuhong, ZHANG Cairong, KANG Long, LUO Yongchun 2007, 24(3): 319-324.  Abstract ( )   PDF (358KB) ( )   Possible geometrical structures and relative stability of (MgB2)n(n=1~3) clusters are studied with a hybrid density functional theory(B3LYP) with 6-31G* basis sets.For the stablest isomers of (MgB2)n(n=1~3) clusters,the electronic structure,vibrational property,bond,ionization potential,polarizability and hyperpolarizability are analyzed. Most of the optimized (MgB2)n(n=1~3) clusters are planar structures and the B-B and B-Mg bonds coexist,while the Mg-Mg bonds are infrequent.The bond lengths of B-B and Mg-B are 0.153~0.182 nm and 0.218~0.231 nm,respectively. Several negative B atoms form an electronegative center and other B and Mg atoms with positive charge are located at the apex of the cluster.The natural charges of Mg atom and B atom are +0.559e~+0.920e and -0.724e~+0.197e,respectively.

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Control of Beam Halo-chaos with Soliton in a Uniform-focusing Channel ZHANG Rong, BAI Long, WENG Jiaqiang, FANG Jinqing 2007, 24(3): 325-329.  Abstract ( )   PDF (232KB) ( )   K-V beam through an axisymmetric uniform-focusing channel is studied in a particle-core model.Beam halo-chaos is observed and a soliton function controller is proposed based on halo formation and the control of halo-chaos.A multiparticle simulation to control the halo by a soliton function controller is performed.It shows that the halo-chaos and its regeneration can be eliminated.

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Resonance Absorption via Mode Conversion in Magnetized Inhomogeneous Plasma HU Youjun, YANG Weihong, CHEN Yinhua, ZHANG Yu 2007, 24(3): 330-336.  Abstract ( )   PDF (398KB) ( )   Resonance absorption of p-polarized electromagnetic wave by mode conversion in magnetized inhomogeneous plasma is investigated numerically as external magnetic field is perpendicular to density gradient.Different from an unmagnetized inhomogeneous plasma,the mode conversion coefficient in a magnetized inhomogeneous plasma depends on a cooperation of the incident direction,the density gradient direction and the direction of external magnetic fied.

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Bulk Flexoelectric Effect in a Nematic Liquid Crystal Cell YE Wenjiang, XING Hongyu, YANG Guochen 2007, 24(3): 337-341.  Abstract ( )   PDF (275KB) ( )   With elastic theory of liquid crystal,we investigate bulk flexoelectric effect in a nematic liquid crystal(NLC) cell with applied voltage.The differential equation of director tilt angle θ is obtained by the variation theory. The distributions of director in a strong anchoring planar aligned cell and in a hybrid aligned nematic(HAN) cell are calculated. The transmittance characteristic of these liquid crystal cells is obtained with Jones matrix method.Influence of bulk flexoelectric effect on the distribution of director and characteristic transmittance of liquid crystal cells are analyzed.

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Radiation Probing Algorithm for Anisotropy Light Source YUAN Bin, LI Jinghong, XU Yan, WANG Hongkun 2007, 24(3): 342-346.  Abstract ( )   PDF (330KB) ( )   We provide a radiant energy probing method based on single contour integration,including annulus probing and uniform probing.It probes the radiant field of an anisotropy light source and is used as an efficient visualization method.

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FDTD Method for Electromagnetic Scattering by Body of Revolution with Obliquely Incident Pulse Plane Wave GUAN Fuhong, CHEN Bin, CHEN Hailin, FANG Dagang, YU Wenming, ZHANG Lijun 2007, 24(3): 347-352.  Abstract ( )   PDF (275KB) ( )   We present a method for electromagnetic scattering with obliquely incident pulse plane wave using BOR-FDTD(body of revolution finite-difference time-domain) method.The obliquely incident pulse plane wave is expanded in a cylindrical coordinate and a total-field/scattered-field formulation is introduced as excitation.The method is validated by comparing with the method of moments.It shows good agreement.

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Extrapolation Boundary Conditions for Total Variation-based Image Deblurring and Denoising XU Jing, SHI Yuying, WANG Xiaoyu 2007, 24(3): 353-360.  Abstract ( )   PDF (506KB) ( )   We propose extrapolation boundary conditions(BCs) for blurring removal.They lead to C1 continuity for one-dimensional signals and C0 continuity with normal derivative continuity for images.Two models and two kinds of blurring operators are used in the extrapolation BCs with Dirichlet,Neumann and antireflective BCs.We apply extrapolation BCs to fast algorithms for total variation-based image deblurring and denoising.Numerical results illustrate efficiency of the extrapolation BCs.

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Numerical Study of Grüneisen State Equation and Applications WANG Tinghui, SONG Shuncheng 2007, 24(3): 361-366.  Abstract ( )   PDF (267KB) ( )   A computational scheme of Runge-Kutta method is presented for Grüneisen state equation with adiabatic impact relation.Thermodynamic state variables,including pressure,Grüneisen coefficient,cold pressure,cold energy and pressure,as a function of specific volume are calculated.Numerical states parameters of tungsten at high-pressure are given.The curves of γ~V,EK~V,PK~V,P~V of tungsten are obtained and the P~V result agrees well with the experiment.Numerical solutions of f(P,T,V1)=0 and f(P,T,V2)=0 in two compressive states show that the effect of temperature on pressure is less than that of specific volume.

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A Method for Periodic Solutions of Stiff Differential Equations QIAO Tiantian, LI Weiguo 2007, 24(3): 367-372.  Abstract ( )   PDF (283KB) ( )   An idiographic method for calculating periodic solutions is proposed as stiff phenomena occur.Program ODE15s for stiff initial value problems is adopted.The Gear's method with variable step length is used and corresponding formula is derived.Numerical example shows good efficiency.

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Different Forms of Nonlinear Schrödinger Equation and Solutions Using Split Step Fourier Method LÜ Lixiang, ZHANG Xiaoping 2007, 24(3): 373-377.  Abstract ( )   PDF (215KB) ( )   The positive and negative frequency expressions of quasi-monochromatic optical fields of a pulse in fiber-optic communication and the positive and negative frequency forms of Fourier transformations and nonlinear Schrödinger(NLS) equations are discussed.Especially,in the solution of pulse spectrum,the negative frequency form of NLS equation should be solved by the negative frequency form of Fourier transformation,while the positive frequency form of NLS equation is solved by the positive frequency form of Fourier transformation.An example is given using split step Fourier method.