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25 July 2005, Volume 22 Issue 4 Previous Issue    Next Issue

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Two Preconditioning Techniques for Two-dimensional Three-temperature Energy Equations WU Jian-ping, LIU Xing-ping, WANG Zheng-hua, DAI Zi-huan, LI Xiao-mei 2005, 22(4): 283-291.  Abstract ( )   PDF (514KB) ( )   In a sparse linear system derived from two-dimensional three-temperature energy equations, the diagonal dominan varies greatly from row to row and so is the magnitude of the elements. We provide a new scaling method to improve the diagonal dominance. As ILUT is used to the derived linear system, it reserves the number of elements in each row and several relatively large elements related to the photon are dropped due to the large difference among elements. To improve the equality of the ILUT, we provide a new method named multiple row ILUT (MRILUT), in which multiple rows are computed before dropping. The provided methods are embedded into a preconditioned Krylov subspace method to solve the actual two-dimensional energy equations with three temperatures. The number of iteration at each time step and the total computation time are both greatly reduced.

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The Application of CPML in Three-dimensional Numerical Simulation of Low-altitude Electromagnetic Pulse GAO Chun-xia, CHEN Yu-sheng, WANG Liang-hou 2005, 22(4): 292-298.  Abstract ( )   PDF (314KB) ( )   According to the characteristics of perfectly matched layers (PML), a convolutional PML (CPML) is chosen to truncate open boundaries used in the numerical simulation of low-altitude electromagnetic pulse. On the basis of the split-field PML and the plane-wave solution of electromagnetic field in a free space, an unsplit-field PML is constructed. With convolutional theorem in the Fourier transformation, discerete iterative equations of electromagnetic field components in the CPML media are presented in three-dimensional prolate-spheroidal coordinate system. The effectiveness of the method in numerical simulation of nuclear electromagnetic pulse is shown.

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An Interpolated Remapping Algorithm for Scattered Physics Quantities WANG Rui-li 2005, 22(4): 299-305.  Abstract ( )   PDF (337KB) ( )   The remapping or coupling of physics quantities across different grids occurs when grids are modified or distinct grids are coupled.This paper presents a few remapping algorithms via the strategies of curve fitting and interpolation.The methods are independent of grid type.

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An Interface Treating Method Based on Riemann Problems WANG Chun-wu, ZHAO Ning 2005, 22(4): 306-310.  Abstract ( )   PDF (250KB) ( )   By predicting the real fluid status rather than the ghost fluid status with a Riemann problem,a simple and efficient extension of the ghost fluid method in multi-dimension is introduced. Riemann problems are constructed at the interface and solved to define boundary conditions of fluid on both sides of the interface.Since the Riemann problem solvers describe fluid state reasonably and the normal velocity and pressure are continuous across the interface,a more accurate interface boundary condition is obtained. Conservation error shows that the method incurs minor errors. Numerical experiments show that this method captures the interface and shock waves correctly.

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Parameter Identification in a 3-D Groundwater Flow Numerical Model: an Improved Genetic Algorithm and the Gauss-Newton Method YAO Lei-hua 2005, 22(4): 311-318.  Abstract ( )   PDF (460KB) ( )   A genetic algorithm (GA) searches in the whole solving space as it deals with nonlinear optimization problems. But in the local solving space, GA is slow and the solution precision is low. The Gauss-Newton Method (GNM) has inverse characters on these points. In this paper, the GA and GNM are used in the parameter identification of ground water flow. GA solves the initial values of parameters. And then, the parameters are identified by GNM. We take 3-dimensional unsteady state flows in an inhomogeneous isotropic confined aquifer as an ideal model, and discuss application of GA and GNM to inverse problem of hydrogeology parameters with finite element method. It is shown that the improved algorithm converges faster and provides higher precision.

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A Finite-Difference Time-Domain Analysis of Electromagnetic Propagation in Magnetized Plasmas HUANG Shou-jiang, LI Fang 2005, 22(4): 319-324.  Abstract ( )   PDF (251KB) ( )   Electromagnetic propagation through a magnetized plasma is studied with the finite-difference time-domain (FDTD) method by means of Z transforms. The propagation direction is perpendicular to the biasing magnetic filed and the electric field is parallel to the biasing magnetic filed. The dependence of the reflection and transmission coefficients on frequency is obtained by discrete Fourier transform. A comparison with analytical values of homogeneous magnetized plasma is made. The reflection and transmission coefficients in an inhomogeneous magnetized plasma layer are calculated as well.

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Classical Trajectories of CO in Laser Fields in the Symplectic Scheme LIU Shi-xing, WANG Huai-min, QI Yue-ying, LIU Xue-shen, DING Pei-zhu 2005, 22(4): 325-328.  Abstract ( )   PDF (200KB) ( )   Classical trajectories of a diatomic molecule system (CO) in laser fields are calculated in the symplectic scheme. The calculated results are compared with that with Runge-Kutta (R-K) approach. The vibration trajectories, phase trajectories and vibration energy of a diatomic molecule CO are analysed.

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An Improvement to Compact Schemes with the Limiting Flux Method TU Guo-hua, LUO Jun-rong 2005, 22(4): 329-336.  Abstract ( )   PDF (376KB) ( )   Limiting flux method is used to improve the compact schemes for discontinuous fluid problems. A limiter is contrived. A series of calculation with third-order to 8th-order schemes are given. It is shown that the limiting flux method provides solutions with high-order accuracy and high resolutions. And it restrains numerical oscillations as well. The limited flux compact scheme is robust in a large range of Mach numbers. It is able to capture discontinuities in fewer grids.

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Associative Memory and Segmentation in a Network Composed of Spiking Neurons PENG Jian-hua, YU Hong-jie, LIU Yan-zhu 2005, 22(4): 337-343.  Abstract ( )   PDF (506KB) ( )   We present temporal segmentation and retrieval of stored memories or patterns with neural networks of a widely used model, the Fitzhugh-Nagumo neurons. For a superposition of several stored input patterns, it is shown that the proposed neuronal network is capable of segmenting out each pattern one after another in the time domain as synchronous firings of a subgroup of neurons. And as a corrupted input pattern is presented, the network is shown to be able to retrieve the perfect one. That is to say it has the function of associative memory. By adjusting parameters as coupling strength and intensity of the noise it is shown that the temporal segmentation attains its optimal performance at intermediate noise intensity, which is reminiscent of the stochastic resonance observed in the coupled spiking neuronal networks.

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Influence of a Ripplet on the Turbulent Flow Behind a Backward Facing Step Wang Xiao-hua, He Zhong-yi 2005, 22(4): 344-350.  Abstract ( )   PDF (333KB) ( )   With the second order Euler-Taylor-Galerkin (ETG) finite element method, a large eddy simulation (LES) is used to simulate turbulent flows over a backward-facing step at Re=47 625. The simulation agrees well with Armaly's experiments.The influence of a ripplet on the turbulent flow is calculated. It is shown that large scale eddies and corresponding reattachment lengths change greatly with the ripplet height and its distance to the step. We argue that adding a ripplet could be a simple and effective passive control to the turbulent flow over a backward-facing step.

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Effects of Stenosis Severity on Pulsating Flow in a Tapered Artery LIU Guo-tao, WANG Xian-ju, AI Bao-quan, LIU Liang-gang 2005, 22(4): 351-357.  Abstract ( )   PDF (374KB) ( )   A mathematical model of pulsating flow in a tapered rigid artery with an axially symmetric stenosis is established. The incompressible Navier-Stokes equation for the flow field is solved numerically and a finite difference scheme is used to implement the numerical calculation. The distributions of the wall shear stress with three stenosis severity (h/R0=1/4,1/3,1/2) are provided and discussd.The stream function contour with h/R0=1/3 is given. The result shows that the stenosis disturbs the flow flied in the vicinity of the stenosis, especially at the throat and in the downstream.

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Numerical Simulations of Detonation in Heterogeneous Explosives in a CTVD Scheme LOU Jian-feng, YU Heng 2005, 22(4): 358-364.  Abstract ( )   PDF (315KB) ( )   A simple and practical high-resolution shock-capturing numerical scheme,CTVD, is applied to numerical simulation of detonation in heterogeneous explosives,in which Lee-Tarver's ignition and growth model is employed,and JWL (Jones-Wilkins-Lee) equation of state is used to both unreacted explosives and reacted gas product. Numerical results for detonation of heterogeneous explosives PBX-9404 and TATB are shown.High resolution in detonation wave and high accuracy in smooth solution region are obtained.Especially in the complicated state equation,numerical results exhibit simplicity,efficiency, and high resolution of the CTVD scheme.

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Implicit Numerical Simulations of an Anisotropic Diffusion Model Driven by Diffusion Tensors LIU Zhao-xia, CHANG Qian-shun 2005, 22(4): 365-370.  Abstract ( )   PDF (271KB) ( )   A model of image processing for anisotropic diffusion driven by diffusion tensors is investigated. An implicit difference scheme is constructed. A large sparse matrix with 13 diagonals is formed with which general iterative methods don't work well. With algebraic multi-grid method (AMG), linear system of equations are solved.Numerical experiments are shown.

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A Study of Flame Instability Wave Propagation Algorithm DONG Gang, JIN Jian-ming, YE Jing-fang, FAN Bao-chun 2005, 22(4): 371-376.  Abstract ( )   PDF (514KB) ( )   Based on the wave propagation algorithm, a numerical scheme of multi-component reactive system is constructed. The interaction between the incident shock wave and the flame bubble, and between the reflected shock wave and distorted flame of the CH4/air mixture are investigated numerically in the Cl4/air elementary reaction model and the splitting method. The evolution and properties of the flame instability induced by incident and reflected shock waves are discussed. The computation indicates that the Helmholtz instability, Richtmyer-Meshkov instability and chemical heat release rate play important roles in the interaction between shock waves and the flame. The calculated results are compared with experimental ones, and an agreement is shown.