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25 March 2007, Volume 24 Issue 2 Previous Issue    Next Issue

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Nonlinear Initial Values in the Iterative Solution of 2-D 3-T Heat Conduct Equations AN Hengbin, MO Zeyao, XU Xiaowen 2007, 24(2): 127-133.  Abstract ( )   PDF (369KB) ( )   As 2-D 3-T heat conduct equations are discretized in a fully implicit method,it is very difficult to solve the nonlinear algebraic equations obtained due to strong nonlinearity.Efficient initial guesses for iterative solutions of discretized nonlinear algebraic equations are presented.Numerical results for two media with different properties show that the proposed initial guesses improve computational efficiency and reduce the influence of nonlinear solver on the time step as well.

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Finite Element Scheme for Fokker-Planck Equation in Plasmas WENG Suming, SHENG Zhengming 2007, 24(2): 134-140.  Abstract ( )   PDF (377KB) ( )   A numerical scheme for the Fokker-Planck equation is proposed with a finite element method,which is relatively simple for implementation and physically clear. It assures a positive distribution function and particle-number conservation without specific requirement on grid and time step.The scheme is confirmed in one-dimensional simulations.It can be extended easily to multi-dimensional cases.

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Numerical Simulation and Parallel Efficiency of Internal Transport with Barrier Trigger in Tokamak Plasmas LONG Yongxing, MU Zongze, DONG Jiaqi, ZHANG Jinhua 2007, 24(2): 141-145.  Abstract ( )   PDF (245KB) ( )   Numerical simulation of dynamic behaviour of internal transport with a barrier trigger in Tokamak plasmas in splitting domain and its parallel computation are shown.The parallel efficiency increases with the computing scale.Numerical results agree well with theoretical analysis.The code adapts to the simulation of nonlinear tearing mode (specially mutiple mode) as well.

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Parallelization of the 2D Multi-Group Radiation Transport Code LARED-R-1 ZHANG Aiqing, MO Zeyao 2007, 24(2): 146-152.  Abstract ( )   PDF (424KB) ( )   In order to realize the parallelization of LARED-R-1,a serial code for numerical simulation of two-dimensional radiation transport,a directed graph is used to accurately describe the data dependencies.A parallel pipeline flux sweeping algorithm is applied to parallelize the code efficiently.Moreover,a special technique of buffering short messages for less communications is presented to improve the parallel performance.For a typical model discretized by 3 800 cells,100 energy groups and 40 directions,tests on a parallel machine show that the parallel LARED-R-1 achieves parallel efficiency by 80% with 64 processors and by 53% with 128 processors,respectively.

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A Spectral Method for Fokker-Planck-Landau Equation WANG Yibo, WANG Shangwu 2007, 24(2): 153-158.  Abstract ( )   PDF (338KB) ( )   A spectral method with FFT transformation is introduced in the numerical solution of the Fokker-Planck-Landau equation in describing charged particle transport in plasma.The time evolution of the distribution function in the velocity-space is studied with a "space-homogeneous" condition.Numerical results show that conservations of mass,momentum and energy are held precisely.In addition,the computation cost is reduced considerably due to the adoption of FFT transformation.

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Moving Least Squares Particle Hydrodynamics with Riemann Solvers HU Xiaoyan, LIN Zhong, NI guoxi 2007, 24(2): 159-165.  Abstract ( )   PDF (327KB) ( )   The moving least squares particle hydrodynamics (MLSPH) is presented and a 1D MLSPH algorithm is discussed.To reduce oscillations near contact discontinuities,two meshfree Riemann problem initial value methods with different accuracy are introduced.The effect of contact interaction between particles is decreased by the Riemann solver.Efficiency of the method is demonstrated by numerical tests of a 1D shock tube.

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A Uniform Method for Unsteady Flows at Arbitrary Mach Number OU Ping, MA Handong, WANG Yiyun 2007, 24(2): 166-170.  Abstract ( )   PDF (303KB) ( )   A uniform method for unsteady flows at arbitrary Mach number is developed.The preconditioned dual-time compressible Navier-Stokes equations for unsteady flows are obtained by incorporating a pseudo-time derivative term and preconditioning.The inviscid flux vectors and the viscous flux vectors are differentiated by a Roe-scheme of three-order and a general central difference scheme,respectively.A pseudo-time subiteration with an implicit ADI-LU scheme is implemented based on state-vector flux linearization.A two-order precision for physical-time step is achieved.Taking low speed flows as examples,the flow over a circular cylinder and the dynamic stall of the NACA0015 airfoil with identical pitching rate are simulated.Computed results agree with published results.It shows that the method simulates unsteady flows at arbitrary Mach number well.

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Large Eddy Simulation of Flows Around a Square Cylinder XIE Zhigang, XU Chunxiao, CUI Guixiang, WANG Zhishi 2007, 24(2): 171-180.  Abstract ( )   PDF (541KB) ( )   The flow around a square cylinder at Re=22 000 is simulated with large eddy simulation (LES).The effect of boundary condition is studied.A mixed finite-volume finite-element method with unstructured grids is adopted to solve filtered compressible Navier-Stokes equations.Though the numerical accuracy is only second order and the grids is relatively coarse,the results are satisfactory and even better than those with much finer meshes.

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Velocity Distribution of Rarefied Gas Flows Through a Rectangular Micro-channel YANG Xuejun, JIANG Jianzheng, FAN Jing 2007, 24(2): 181-186.  Abstract ( )   PDF (283KB) ( )   We employ the information preservation (IP) method and the direct simulation Monte Carlo (DSMC) method to calculate a plane Poiseuille flow from the continuum regime to the free-molecule flow regime.The Beskok-Karniadakis formula is corrected and kinetic factor of mass flow rate is re-fitted.A velocity distribution applicable to the entire flow regime is derived.

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An Improved Genetic Algorithm for Groundwater Pollution FAN Xiaoping, LI Gongsheng 2007, 24(2): 187-191.  Abstract ( )   PDF (284KB) ( )   An inverse problem method is employed to determine the average magnitude of acid pollutants in groundwater in Fengshui,Zibo,Shandong.Numerical testifications show that an improved genetic algorithm based on optimal perturbation analysis is feasible and efficient.It sucessfully estimates the magnitude of groundwater pollutions in the region.

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Effects of Geometric Parameters on Steady Laminar Heat Transfer in Wavy Channels XIE Gongnan, WANG Qiuwang, ZENG Min, LUO Laiqin 2007, 24(2): 192-196.  Abstract ( )   PDF (312KB) ( )   Periodically fully developed convective heat transfer characteristics in a two-dimensional wavy channel are investigated numerically with a constant wall temperature.The calculations are performed with Pr=0.7,Re=20~500 on non-orthogonal non-staggered grids generated by an elliptic equation system.A semi-implicit method for pressure linked equations revised (SIMPLER) algorithm in curvilinear body-fitted coordinates is employed.Effects of Reynolds number and geometric parameters,such as aspect ratio φ and shape ratio γ,on heat transfer and friction factor are studied.It shows that no recirculation region occurs through the whole channel at low Reynolds numbers,small aspect ratio or small shape ratio.With the increase of Reynolds number,aspect ratio or shape ratio,heat transfer is enhanced due to flow recirculation.Corresponding friction factor increases simultaneously.

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Non-Darcy Flow Analysis of Fluid in Deformed Fractal Reservoir with Double Porosity MA Xiaodan, TONG Dengke, MA Huawei 2007, 24(2): 197-202.  Abstract ( )   PDF (292KB) ( )   We establish a flow equation stress_sensitive to permeability for fractal and deformed double porous media and introduce permeability modulus of double porous media fractal reservoir.Numerical calculation in a fractal double porous media model with constant rate production or constant pressure production in an infinitely large system is carried out with the Douglas_Jones predictor_corrector method.Typical pressure curves are shown.

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Weighted Essentially Non-oscillatory Schemes for Image Restoration SHI Yuying, CHANG Qianshun 2007, 24(2): 203-210.  Abstract ( )   PDF (420KB) ( )   Weighted essentially non-oscillatory schemes are described in detail for a total variation-based image restoration problem with Gaussian kernel at different boundary conditions.Numerical results with three methods (weighted essentially non-oscillatory schemes,wiener algorithm and a combination of them) are compared. Experimental results demonstrate effectiveness of the combination of weighted essentially non-oscillatory schemes and wiener algorithm.

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Wave Equation Migration in Angle Domain CHEN Shengchang, MA Zaitian, WU Ru-Shan 2007, 24(2): 211-216.  Abstract ( )   PDF (596KB) ( )   In the wave equation depth migration of common shot gathers,the windowed Fourier frame expansion of seismic wavefield is used to obtain the receiver and source wavefields in the local angle domain.We propose a wave equation migration method in angle domain for common shot gathers seismic data.With migration in angle domain,the image matrix in local angle domain,the migration sections with different common-dip angles and reflection angles at imaging points are obtained.It provides fundamental data for processing approaches based on migration,such as analysis of amplitude versus angle,extraction of common image gather in angle domain and velocity analysis in angle domain. Numerical examples in a steep dip model and an international standard Marmousi model show that the wave equation migration method in angle domain is correct and effective.

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Error Estimation and Mean Value Interpolation on Polygonal Elements WANG Zhaoqing, LI Shuping 2007, 24(2): 217-221.  Abstract ( )   PDF (294KB) ( )   With shape functions of mean value interpolation and a bivariate Taylor expression,error estimation of mean value interpolation within polygonal elements is analyzed.Inequality of error estimation for mean value interpolation is derived.Mean value interpolation in the approxmation of temperature distributions on a convex domain is shown.

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Magnetic Properties of a Mixed One-dimensional Ferrimagnetic Spin Chain:Monte Carlo Simulation SHEN Shuangjuan, JIANG Liqin, YANG Yanmin, FENG Qian, HUANG Zhigao 2007, 24(2): 222-226.  Abstract ( )   PDF (310KB) ( )   Monte Carlo simulation is performed to study the magnetic properties of mixed spin-1 and spin-3/2 ferrimagnetic systems in a one-dimensional spin chain with single-ion anisotropy.It is found that magnetization plateaus in external fields at ground state exist.A phase diagram of mixed spin-1 and spin-3/2 ferrimagnetic systems is obtained.The magnetic plateaus and the phase diagrams of the system are explained well with analysis of energy and spin configuration.

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Optimal Design of a Multi-wavelength Broadband Raman Amplifier CHANG Jianhua, WANG Tingting, TAO Zaihong, ZHANG Mingde 2007, 24(2): 227-233.  Abstract ( )   PDF (458KB) ( )   Power coupled equations for a multi-wavelength broadband Raman amplifier (MBRA) are reasonably simplified.A multi-step average power method is used to compute composite Raman gain of multi-signal in a dense wavelength division multiplexed system (DWDM).A conventional simulated annealing algorithm is applied for optimization of MBRA.A simple object function is proposed considering the gain bandwidth,on-off gain,gain flatness and other characteristic parameters.Influences of the number of pump,input power and wavelength distribution on Raman gain are studied.Relations among gain bandwidth,on-off gain,gain flatness and the number of pump of MBRA are revealed.Simulation shows that the optimal signal bandwidth Δλ becomes boarder with the increasing of the number of pump and narrower with the increasing of Raman gain and the improvement of flatness.

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Off-lattice Model for Protein Folding TAN Xiaochao, HE Hongbo, LI Yibing 2007, 24(2): 234-238.  Abstract ( )   PDF (347KB) ( )   A simplified off-lattice model of protein is studied with a PSO algorithm.Interaction between atoms is represented by a physical-based potential.The protein's RMSD value between computed and experimental structures is 6.12Å in optimizing the potential in global space. The protein total energy and radius of gyration at PSO steps and the relation between minimum energy and corresponding RMSD value are investigated.It shows basic characteristics of protein folding.

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Domain Decomposition Explicit/Implicit Scheme with Modified Upwind Method for Parabolic Equations LI Changfeng, YUAN Yirang 2007, 24(2): 239-246.  Abstract ( )   PDF (365KB) ( )   An efficient domain decomposition scheme for parabolic equations is discussed,which applies a modified upwind approximation to the first-order derivative.For parallel computation the scheme employs implicit procedures in subdomains and adopts explicit calculations with inter-domain boundaries.With a weaker stability constraint,error estimate in a discrete l2 norm is presented.Theoretical analyses are validated by numerical experiments.

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A General-purpose Two-dimensional Semiconductor Simulator GONG Ding, WANG Jianguo, ZHANG Dianhui, ZHANG Xianghua, HAN Feng, TONG Changjiang, ZHANG Maoyu 2007, 24(2): 247-252.  Abstract ( )   PDF (309KB) ( )   We develop a general-purpose two-dimensional semiconductor simulator (GSS),by which the drift-diffusion model and hydrodynamic model are calculated.It calculates steady-state and transient responses of the devices with different materials structures and is applied to an NPN transistor and MESFET.IV curves,electron density distribution and temperature variation are obtained.