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25 September 2007, Volume 24 Issue 5 Previous Issue    Next Issue

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A Rezone Strategy of Adaption to Variation of Flow Variables YONG Heng, YUAN Guoxing, CHENG Juan, WANG Zheng 2007, 24(5): 505-511.  Abstract ( )   PDF (346KB) ( )   A nine-point rezone strategy is presented,which improves geometric quality of computational grids and keeps the rezoned grids close to Lagrangian meshes.The scheme is proved an approximation to elliptic equation with spherical symmetry.Numerical examples demonstrate robustness and effectiveness of the scheme in ALE (Arbitrary Lagrangian Eulerian) calculation of high speed impact and denotation driving.

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An Adaptive Method Based on Variational Principle in a Unified Coordinate System YAO Wen, ZHAO Guiping, WANG Shuanghu 2007, 24(5): 512-518.  Abstract ( )   PDF (240KB) ( )   Variational methods are used in a unified coordinate system.The mesh spacing, smoothness,orthogonality and regularity of grids are considered to obtain an elliptic equation for h.Typical examples demonstrate that it is possible to use variational methods in a unified coordinate system,and the distribution of h satisfies different boundary conditions.

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Unified Coordinate System for Axisymmetric Compressible Flow GAO Bo, WU Ziniu 2007, 24(5): 519-525.  Abstract ( )   PDF (313KB) ( )   We extend the unified coordinate system proposed by Hui et al.to axisymmetric Euler equations.The form and hyperbolicity of axisymmetric Euler equations are discussed.Solution of 1-D Riemann problem solved by axisymmetric Euler equations after dimensional splitting is shown.Axisymmetric Euler equations are numerically solved using Godunov scheme with MUSCL update.Numerical results show advantages of unified coordinates.

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Unstructured Subzonal Pressure Method GE Quanwen, LIN Zhong, WANG Ruili 2007, 24(5): 526-532.  Abstract ( )   PDF (396KB) ( )   The subzonal pressure is obtained with subzonal Lagranian masses and corresponding densities. It results in subzonal corner forces and eliminates hourglass motion and spurious vorticity.We extend the compatible Lagranian hydrodynamics algorithm including subzonal pressures to unstructured zone and develope the code.Numerical examples of Saltzman piston demonstraste that this algorithm captures shock discontinuity,eliminates hourglass motion and restraines spurious vorticity accuratly and efficiently.

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A High-order Unsteady Shock-fitting Scheme ZHANG Yudong, FU Dexun, MA Yanwen, LI Xinliang 2007, 24(5): 533-536.  Abstract ( )   PDF (196KB) ( )   Based on a high-order compact upwind scheme,a high-order shock-fitting finite difference scheme is studied for numerical simulation of the generation of boundary layer disturbance waves due to free-stream waves.Both steady and unsteady flow solutions of the receptivity problem are obtained by computing full Navier-Stokes equations.Numerical simulation of receptivity to free-stream disturbances for hypersonic boundary layers is performed.

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Numerical Study on Several Godunov-type Schemes with ALE Formulation TIAN Baolin, SHEN Weidong, LIU Yan, CHENG Junbo, WANG Shuanghu 2007, 24(5): 537-542.  Abstract ( )   PDF (263KB) ( )   A Godunov-type ALE (Arbitrary Lagrangian-Eulerian) method based on finite volume technique is developed to simulate compressible multimaterial flows with large deformation.The method adapts well to Lagrangian,ALE or Eulerian formulations due to its arbitrary moving speed of meshes.Numerical features are studied in the formulations.Numerical traits of several Godunov-type schemes are studied.Resolutions of scheme for shock and contact are compared.

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A Finite Volume ALE Method Based on Approximate Riemann Solution JIA Zupeng, YU Xijun 2007, 24(5): 543-549.  Abstract ( )   PDF (263KB) ( )   ALE (Arbitrary Lagrangian Eulerian) finite volume method for compressible fluid flows on moving quadrilateral meshes in two dimensional planar coordinates and axisymmetric coordinates is studied.A vertex-centered finite volume method and an HLLC numerical flux adapted to various equations of state are employed.A second order accuracy in space is achieved by using a reconstruction of primitive variables based on WENO approach.An explicit two-stage Runge-Kutta time-stepping scheme is used in discretization of time.The method offers accurate and robust solutions in capturing strong shock,contact discontinuities and material interface on arbitrarily moving grids.

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Numerical Simulation of Electromagnetic Scattering from a 3-D Target over a Randomly Rough Surface Using FDTD Method KUANG Lei, JIN Yaqiu 2007, 24(5): 550-560.  Abstract ( )   PDF (591KB) ( )   A numerical finite-difference time-domain(FDTD) approach for electromagnetic scattering from a dielectric target over randomly rough surface is developed in a three dimensional model.The rough surface is truncated in the simulation by using periodic surface extension.One period of rough surface is related to the surface correlation length.Generation of incident waves upon a rough surface is presented.Numerical model of a target on/above a rough surface is designed.Polarized bistatic scattering from the target and rough surface is obtained based on numerical distribution of near fields.A comparison of three-dimensional and conventional two-dimensional models is made.It shows that the back scattering from a rough surface is significantly enhanced due to the target on/above the rough surface.

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Edge Element Analysis of Electro-Magnetic Waveguide Based on Symplectic System YANG Hongwei, ZHONG Wanxie, SUI Yunkang 2007, 24(5): 561-565.  Abstract ( )   PDF (176KB) ( )   Based on the Hamilton formulation of electro-magnetic waveguides,a finite element semi-analytical transverse discretization with symplectic formulation is used to solve waveguides with complicated cross sections.The method is applicable to arbitrary an-isotropic materials and is easy to deal with interface conditions between different materials.It can be used to solve complicated problems difficult with analytical methods.The edge element is used in discretization.Rectangular waveguide,rectangular waveguide with T-septum and layered waveguide are studied.Numerical results approximate to theoretical results and do not show spurious solutions.

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Time-biased FDTD Method for Particle-in-cell Simulation ZHOU Jun, ZHU Dajun, LIU Dagang, LIU Shenggang 2007, 24(5): 566-572.  Abstract ( )   PDF (315KB) ( )   An effective finite-difference time-domain (FDTD) method,timebiased FDTD method,is developed to filtrate high-frequency noise for particle-in-cell (PIC) simulation.The formula is derived using time bias and relaxation iterations on the basis of centered-difference FDTD method.Stability and convergence of this method are analysed. In the computation of a relativistic magnetron,compared with the centered-difference FDTD method,filter efficiency of this method is shown.

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A Class of Meshless Methods for Heat Conduction Equations LI Shoufu, ZHANG Yuan, LIU Yuzhen 2007, 24(5): 573-580.  Abstract ( )   PDF (344KB) ( )   A class of meshless methods for heat conduction equations are constructed.They can be performed on structured or unstructured meshes.The methods are conservative and consistent.They have at least the first order accuracy when performed on irregular quadrilateral or triangular meshes,and have the second order accuracy when performed on rectangular or uniform parallelogram meshes. These meshless methods are suitable and efficient in solving linear or nonlinear parabolic problems on irregular quadrilateral meshes or mixed meshes, especially in solving two-dimensional three-temperature radiation heat conduction equations on irregular and mixed meshes.

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An Improved ICCG Method for Large Scale Sparse Linear Equations ZHANG Yongjie, SUN Qin, LI Jianghai 2007, 24(5): 581-584.  Abstract ( )   PDF (178KB) ( )   Based on incomplete Cholesky decomposition with two thresholds,we propose an improved incomplete Cholesky conjugate gradient (ICCG) method with diagonal elements modification.It ensures accurate and efficient decomposition and solution of large scale sparse linear equations. The method shows advantage in computing time and storage requirment.It is applicable to solve the systems of linear equations from FEM finite element method.

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Dynamical Simulation of Magnetic Nano-drug Targeting KANG Bin, SONG Wei, ZHANG Yan, DAI Yaodong, CHEN Da 2007, 24(5): 585-590.  Abstract ( )   PDF (351KB) ( )   We describe an unsteady flow model of blood in arterioles of normal and tumor tissues,and show effect of external magnetic field on flow field of blood considering coupling of magnetic field and flow. Traditional single-phase model is modified by a discrete method,and dynamical simulation with a finite element route is used to investigate transmission of magnetic nano-drug in arteriole.The result indicates that the capture of nano-drug by magnetic field is entirely different from that of microdrug by magnetic field.The trajectoriy of nano-drug is primarily coincident with the streamline of blood flow.However,the effect of magnetic field on the blood flow is obvious due to the presence of magnetic nano-drug.Several whirlpools are formed near the magnet.In tumor arteriole these whirlpools stay for a long time and the magnetic nano-drug is efficiently captured by external magnetic field.

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Numerical Study on Self-sustained Oscillation in Cavity Flameholders of Scramjets SUN Mingbo, LIANG Jianhan, WANG Zhenguo 2007, 24(5): 591-597.  Abstract ( )   PDF (332KB) ( )   Self-sustained oscillation of supersonic cold flowover cavities of scramjets is investigated.Unsteady flowfields are calculated by hybrid RANS/LES method.The key cavity parameters,cavity aft wall angle andthe ratio of cavitylengthto depth,are considered.The hybrid model captures the large scale unsteady characteristics and reveals the evolution process of cavityfree shearlayer.Pressure fluctuation spectra agree well with theoretical prediction.The hybrid RANS/LES data indicate that both cavity shape and size have significant effects on oscillation.Asthe ratio of cavitylengthto depth decreases,the oscillations tend to concentrate on several modes,and the frequency of maximumoscillation amplitude shifts to higher values.Most oscillations are greatly attenuate as the cavity aft wall angle decreases.Compared with a steep aft wall cavity,only highfrequency mode remains inthe cavity with small aft wall angle.

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Continuum-based Model and Its Validity for Micro-nozzle Flows ZHANG Genxuan, WANG Lu, ZHANG Xianfeng, LIU Minghou 2007, 24(5): 598-604.  Abstract ( )   PDF (328KB) ( )   Two-dimensional and three-dimensional simulations are performed to investigate supersonic cold gas flows in micro-nozzles using continuum-based no-slip and slip models,respectively.The validity of continuum-based models is examined by DSMC method.The study focuses on low Reynolds number effects,three-dimensional effect and propulsive performance of the micro-nozzle flow.It shows that compared to the prediction of propulsive performance,the simulation of local flow fields needs a more stringent model.The no slip N-S equations are able to predict propulsive performance of micro-nozzles with Kn < 0.03.Reynolds number is a key parameter in governing low Reynolds number effect and propulsive performance.The strong viscous losses can be mitigated and better propulsive performance can be achieved at higher chamber pressures.The micro-nozzle with the ratio of etch depth to throat width more than 13 has a good 2D characteristic as Re > 1000.

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Pseudo-homogeneous Modeling of Un-stabilized Filtration Combustion ZHANG Genxuan, ZHAO Pinghui, ZHU Minming, CHEN Yiliang 2007, 24(5): 605-611.  Abstract ( )   PDF (334KB) ( )   Based on a one-dimensional laminar reactive flow model,a new pseudo-homogeneous model is constructed and adopted in quasi-steady-state simulation of low-velocity filtration combustion in a packed bed under fully developed conditions.Influences of dispersion effect and reaction mechanisms are discussed in detail by comparsion of the conventional two-phase model with the pseudo-homogeneous model.Effects of various transport terms on different conservation equations are studied.The performance of quasi-steady-state and transient analytical solutions is evaluated by comparing with pseudo-homogeneous model.

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Nonlinear Prediction and Analysis of EEG in a Liley Model WANG Xingyuan, TAN Guilin 2007, 24(5): 612-618.  Abstract ( )   PDF (419KB) ( )   Nonlinear prediction and RBF (Radial Basis Functions) neural network prediction of EEG(Electroencephalogram) signal in a Liley model are studied by phase graph and NLCP (Nonlinear Cross-Prediction).It concluded that:1) RBF neural network prediction is better than nonlinear prediction;2) NLCP method is adaptive to time series with strong periodic components;3) support the exist of chaos in EEG signals.

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An Adaptive Hybrid Inversion Algorithm for Ellipsometric Measurement of Thin Films JING Xili, XU Tianfu, CHEN Xiujuan, LI Dongyu 2007, 24(5): 619-624.  Abstract ( )   PDF (279KB) ( )   A hybrid optimization algorithm is developed for solving ellipsometric measurement problem.This algorithm is based on the high ability of simulated annealing method in seeking optimum solution and the high computation efficiency of simple shape method.It seeks the global minimum solution of objective function and gets proper parameters of optical model.The computation efficiency is higher than that of simulated annealing algorithm.The selection of inversion controlling parameters is discussed to make this algorithm adaptive.

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Numerical Simulation of Sphere Packing with Arbitrary Diameter Distribution ZHAO Liang, LI Shuixiang, LIU Yuewu 2007, 24(5): 625-630.  Abstract ( )   PDF (358KB) ( )   A relaxation algorithm is developed to simulate sphere packing with arbitrary diameter distribution.An adaptive iteration period is employed to keep the packing density stable with various number of spheres.The packing density and the coordinate number of the algorithm are higher than those of previous approaches.The efficiency of contact detection is considerably increased by background grids and double link group structure.The time complexity of the algorithm is O(N),where N is the number of spheres.It needs only CPU time of 217s to achieve a packing density of 0.64 for random close packing of 10 000 equal spheres with an AMD Athlon 3200+PC.New classification of numerical methods for sphere packing is also presented.