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25 March 2011, Volume 28 Issue 2 Previous Issue    Next Issue

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Lagrangian Finite Point Method for Two-dimensional Compressible Flows SUN Shunkai 2011, 28(2): 159-166.  Abstract ( )   PDF (579KB) ( )   A Lagrangian finite point method for two-dimensional compressible hydrodynamics problems is presented.The numerical scheme is based on scattered points inside a computational domain without need for a specific connectivity.A cloud of five neighbors is selected around each point at each time step,and this cloud is used to implement finite point schemes based on five-point approximation formulas to gather information about flow derivatives.For numerical stability concerns,four artificial Laplace operators are introduced and added to corresponding conservative equations,respectively.Furthermore,an adaptive strategy for time step is also provided.Numerical results show validity and potential interest on this approach.

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Improvement on Window Embedment Technology with High Order Conservative Remapping ZHANG Yufei, CHEN Haixin, FU Song 2011, 28(2): 167-173.  Abstract ( )   PDF (910KB) ( )   High-order conservative remapping method is developed to improve flow information exchange accuracy of window embedment technology on non-matched grid-block interface with preservation of conservative property and robustness.Remapping methods with various order of accuracy combined with various stencil selection strategy are compared.Constant distribution,linear and quadratic polynomial distributions are tested for reconstruction of conservative variables on interface.Accuracy and efficiency of linear polynomial WENO remapping are balanced well for engineering application.Numerical study of DLR-F4 wing-body configuration with a mending plate patched on the wing is conducted by a in-house developed code NSAWET.A sharp pressure jump brought by the mending plate is predicted.

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An Adaptive Explicit Time Integration Algorithm for Hydrodynamic Equations and Application in ICF LIU Qingkai, XU Xiaowen, WU Junfeng 2011, 28(2): 174-180.  Abstract ( )   PDF (609KB) ( )   An adaptive time integration algorithm is proposed for ADE(alternating direction explicit based on dimension splitting) scheme.Based on the algorithm,a parallel adaptive program for multi-material hydrodynamics is developed on JASMIN.An implosion experiment in ICF(inertial confinement fusion) is simulated on 512 processors.Both simulation results and performance analysis demonstrate correctness and efficiency of the algorithm and the code.

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Parallel Finite Element Algorithms Based on Fully Overlapping Domain Decomposition for Time-dependent Navier-Stokes Equations SHANG Yueqiang, HE Yinnian 2011, 28(2): 181-187.  Abstract ( )   PDF (309KB) ( )   Based on fully overlapping domain decomposition,three parallel finite element algorithms for time-dependent Navier-Stokes equations are proposed.Basic idea of algorithms is to discretize spatial space with fully overlapping domain decomposition technique,and then to solve ordinary differential equations with respect to time independently in backward Euler scheme on overlapped subdomains.The nonlinear convective term is dealt with semi-and fully-implicit schemes,respectively.In these algorithms,each subproblem is a global problem with vast majority of degrees of freedom associated with a particular subdomain that is responsible for,which allows algorithms to be implemented easily with low communication costs.Numerical test illustrates efficiency and good parallel performance of the algorithms.

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High-order Hybrid DG/FV Schemes Based on“Static Re-construction”and“Dynamic Re-construction”for Two-dimensional Conservation Law ZHANG Laiping, LIU Wei, HE Lixin, HE Xin, DENG Xiaogang 2011, 28(2): 188-198.  Abstract ( )   PDF (647KB) ( )   With study of finite volume(FV) methods and discontinuous Galerkin(DG) method,"static reconstruction" and "dynamic reconstruction" are proposed for high-order numerical schemes.Based on the concept of "hybrid reconstruction",a new class of hybrid DG/FV schemes is presented for two-dimensional(2D) unstructured grids to solve the 2D conservation law,including 2D scalar equations and Euler equations.In the hybrid DG/FV schemes,lower-order derivatives of the piecewise polynomial are computed locally in a cell by a traditional DG method(called "dynamic reconstruction"),and the higher-order derivatives are reconstructed by the "static reconstruction" of the FV method by using lower-order derivatives in the cell and immediate neighbour cells.Typical 2D cases are given,and accuracy study is carried out.Numerical results show that the hybrid DG/FV scheme reaches desired order of accuracy.In addition,the hybrid DG/FV scheme saves great CPU time and memory compared with same order DG schemes.

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Numerical Schemes for Detonation Front on Curvature on Unstructured Quadrilateral Meshes CHENG Junxia 2011, 28(2): 199-206.  Abstract ( )   PDF (509KB) ( )   Assuming that detonation normal velocity is a linear function of curvature,we study propagation of detonation front on unstructured quadrilaterals with level set method.Convection term in leve set equation is solved by positive scheme,and curvature term is solved by Galerkin isoparametric finite element method and semi-implicit time stepping.On Cartesian meshes and random meshes,the scheme of level set equations containing curvature is more than first order accuracy in L2 and L∝ norms.Examples of nonsmooth level sets shortening and three detonation fronts colliding show that the schemes can be used to simulate propagation of detonation front on curvature.

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Numerical Simulation of Hypervelocity Impact with Subdomains in SPH Computation BIAN Liang, WANG Xiaojun, ZHANG Jie, ZHAO Kai 2011, 28(2): 207-212.  Abstract ( )   PDF (585KB) ( )   Considering the fact that large deviatoric deformations are always localized in a small narrow region in hypervelocity impact problems,a method named subdomain computation for SPH(smoothed particle hydrodynamics) is developed.The entire computational domain is divided into several subdomains.In subdomains where large deformation is developed more particles are placed,and in subdomains where only small deformation is developed fewer particles are placed.Computational instability induced at interface of two subdomains is discussed and a method to handle the instability is proposed.Numerical simulations of a rod projectile penetrating into a thick target are carried out with the method and traditional SPH.It shows that computation accuracy as well as computation efficiency are improved.

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A General Study on Post-processing of Smoothed Particle Hydrodynamics ZHENG Jun, YU Kaiping, WEI Yingjie, ZHANG Jiazhong 2011, 28(2): 213-218.  Abstract ( )   PDF (423KB) ( )   We propose a method for data-visualization of smoothed particle hydrodynamics(SPH).Data calculated with SPH on convex or non convex continuum domain are processed.Particle set is discretized into a set of triangular elements by Delaunay triangulation,and only those elements on which nodes interact with each other are kept.With kept elements and data on their nodes a finite element interpolation is employed to derive values on interior points of the elements.A free surface is easily extracted with the method.Feasibility of the method is tested.Methods dealing with walls,severe particle splashing or multi-materials are provided,respectively.They supply feasible ways for realizing a general post-processing software package for SPH and even for gridless methods.

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A Coupling Algorithm of Finite Element and Smoothed Particle Hydrodynamics XIAO Yihua, HU Dean, HAN Xu 2011, 28(2): 219-224.  Abstract ( )   PDF (580KB) ( )   A coupling algorithm of finite element(FE) and smoothed particle hydrodynamics(SPH) is introduced.It couples FE calculation with SPH calculation by attaching particles to element segments.In the algorithm,a particle can be fixed to an arbitrary position of an element segment and an element segment can be attached to many particles simultaneously.This makes arrangements of particles and elements at the coupling interface free.The algorithm is applied to simulate stress-wave propagation and high-velocity impact problems.It shows that the algorithm has good accuracy in simulation of stress-wave propagation.In high-velocity impact problems it achieves nearly same accuracy with higher efficiency compared with pure SPH algorithms.

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Lattice Boltzmann Simulation of Flow in a Micro-channel ZHANG Renliang, DI Qinfeng, WANG Xinliang, GU Chunyuan, WANG Wenchang 2011, 28(2): 225-229.  Abstract ( )   PDF (371KB) ( )   A droplet with constant driving force moving inside a micro-channel is studied in a lattice Boltzmann model and a Shan-Chen multiphase model.Flow regimes under different wall wettability and topography are investigated.It is clarified that hydrophobic surface with certain roughness can reduce fluid flow resistance.It is found that flow behaviors are strongly affected by wall wettability and surface roughness.It shows that the method is efficient and accurate.It has good prospect on the study of drag reduction of microscopic seepage of reservoirs.

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A Computational Method for Productivity of Horizontal Well in Naturally Fractured Reservoirs CHENG Linsong, PI Jian, LIAN Peiqing, HUANG Shijun 2011, 28(2): 230-236.  Abstract ( )   PDF (329KB) ( )   Based on flow characteristics of horizontal wells in naturally fractured reservoirs,vadose area is divided into two zones: near wellbore zone and far wellbore zone.The far wellbore zone is featured by its continuous homogeneity.In near wellbore zone,a coupling model is established considering fluid flow in fracture and horizaontal well simultaneously.Principles of potential superposition and mirror reflection as well as the concept of infinitesimal line congruence are used in the model.Combining flow characteristics of the far and near wellbore zones,a comprehensive computational method for fractured hoizontal well productivity is presented.A practical case is used to verify this method.Computational result shows that productivity of horizontal well calculated with this method is closer to actual flow rate than theoretical formula.Productivity of horizontal well increases as fracture density rises,but increment of productivity decreases as fracture density increases.

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Two-step Interpolation Method for Multilevel Fast Multipole Algorithm XIANG Daopu, ZHOU Dongming, HE Jianguo 2011, 28(2): 237-242.  Abstract ( )   PDF (303KB) ( )   A multilevel fast multipole algorithm(MLFMA),based on fast multipole method(FMM),is implemented with aggregation,translation and disaggregation stages to optimize computational complexity.Local interpolations are required in aggregation and disaggregation stages of MLFMA in order to match sampling rates of radiated and incoming fields in consecutive levels.A conventional one-step method is decomposed into two one-dimensional interpolations applied successively.Due to significant acceleration in processing time,the proposed two-step method is especially useful for large-scale objects discretized with millions of unknowns.

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An Arithmetic for Filtrating High-frequency Noise in Particle-in-cell Simulation LIU Dagang, ZHOU Jun, YANG Chao, MENG Lin 2011, 28(2): 243-249.  Abstract ( )   PDF (360KB) ( )   Mechanism of high-frequency noise in particle-in-cell(PIC) simulation is analysed.An effective finite-difference time-domain(FDTD) method called High_Q FDTD method is developed in which high-frequency noise is filtrated and high quality factor device is calculated with PIC simulation.Formulation of the method is derived on the basis of time-biased and centered-difference FDTD method.Stability and convergence of this method are well analysed.Filter efficiency and calculation precion of this method are compared with those of the time-biased and centered-difference FDTD method in computation of a relativistic backward wave oscillator(RBWO).

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Electron Energy Distribution in Radio-frequency CH4 Plasma LV Shaobo, LIN Zeng, WANG Qing, BA Dechun 2011, 28(2): 250-258.  Abstract ( )   PDF (1338KB) ( )   Electron energy distribution function(EEDF) in RF methane plasma is calculated with Boltzmann equation and Lorentz approximation. Instead of a self-consistent RF field satisfying Poisson's equation,a simple electric field distribution is used.6 neutrals are included,as well as 27 electron-neutral reactions.EEDF yields information about electron reaction rates in plasma,electron average energy,and transport coefficients.In the sheath region,EEDF is Maxwellian,and in the bulk region a Druyvesteyn EEDF is found.An electron average energy peak occurs in the sheath region,together with electron reaction rates.Differing from constant transport coefficients used in references,electron diffusion and mobility coefficients strongly depend on RF period and space.

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High-order CIP Numerical Method and Applications in Vlasov-Poisson Equation FU Deyue, PENG Xiaodong 2011, 28(2): 259-267.  Abstract ( )   PDF (496KB) ( )   A high-order CIP(Constrained Interpolation Profile,HCIP) method is developed by constructing a high-order interpolation function based on high-order spatial derivatives.Numerical errors of both HCIP scheme and a standard CIP(SCIP) scheme proposed by Yabe and et al are studied.With HCIP method,we investigate numerically physical problems in the famous Vlasov-Poisson equation,such as Landau damping and two-stream instability.It shows that HCIP method is a fifth-order accuracy scheme.Its accuracy is higher than that of SCIP method.Dynamical evolution due to Landau damping in an electrostatic plasma simulated by HCIP method agrees well with previous results.By reducing the number of grids calculation speed is increased with same accuracy.

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Self-optimizing Cumulative Inversion of Particle Size Distribution with Photon Correlation Spectroscopy QIU Jian, YANG Guanling, HAN Peng, CHEN Chaoxiong 2011, 28(2): 268-274.  Abstract ( )   PDF (382KB) ( )   A self-optimizing cumulative inversion for particle size distribution with photon correlation spectroscopy is proposed.It improves precision and stability of measurement.From a detailed fundamental of photon correlation spectroscopy and conventional cumulative inversion,we analyze instability of cumulative inversion.A self-optimizing method is presented by using the minimum mean-square error.It inverts particle size distribution stably with scattered autocorrelation curve with random noise.Experimental results illustrate validity and feasibility of the approach.

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Symplectic Fourier Pseudo-spectral Schemes for Klein-Gordon-Schrödinger Equation WANG Lan, MA Yuanping, KONG Linghua, DUAN Yali 2011, 28(2): 275-282.  Abstract ( )   PDF (293KB) ( )   Symplectic Fourier pseudo-spectral integrators for Klein-Gordon-Schrödinger equations(KGS) are investigated.A Hamiltonian formulation is presented.Fourier pseudo-spectral discretization is applied to the space approximation which leads to a finite-dimensional Hamiltonian system.Symplectic integrators,including Störmer/Verlet method and midpoint rule,are adopted in the time direction which leads to symplectic integrators for KGS.It suggests that the Störmer/Verlet method is explicit which can be coded effciently,and the midpoint rule captures mass of the original system exactly.Numerical experiments show that symplectic integrator can simulate various solitary well over a long period.

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An Algorithm for Two-dimensional Discrete Hartley Transform DONG Zhifang, WU Jiasong, SHU Huazhong 2011, 28(2): 283-288.  Abstract ( )   PDF (450KB) ( )   We present a moment-based fast algorithm for efficient computation of two dimensional(2-D) discrete Hartley transform(DHT).With a kernel map and Taylor expansion,2-D DHT is approximated by a linear sum of 2-D discrete moments.Computation of moments is realized in an all adder systolic structure.The algorithm is efficient and suitable for dealing sequence of any length with high precision.MRI image compressions show that the method can reach high peak signal-to-noise ratios.

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Structure of Liquid Aluminum Oxide:A Molecular Dynamics Study WU Yanning, WANG Liping, ZHU Yiqiang, HUANG Yinsheng, WANG Daimu 2011, 28(2): 289-294.  Abstract ( )   PDF (587KB) ( )   With molecular dynamics study,we investigate microstructure of liquid Al2O3 at 2663 K and 2223 K.The first and second nearest-neighbor distances are in good agreement with results of Ansell et al.Analysis on coordination numbers and angle-distribution functions show that the microstructure of liquid aluminum oxide mostly consists of three-fold coordination of oxygen,four-fold and five-fold coordination of aluminum.Evidence of liquid-liquid phase transition due to separation of high and low coordinate species is not found.

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Electronic Transport in Molecular Device of Isomers LIU Ruijin, LI Zongliang, WANG Chuankui 2011, 28(2): 295-300.  Abstract ( )   PDF (324KB) ( )   With ab initio theory and elastic scatering Green's function method,current and conductance of heterocyclic molecular isomers are investigated.It shows that expending orbits and coupling coefficients have dominant influence on electronic transport of molecular systems.Positions of nitrogen atoms and terminal atoms in molecules affect expending of molecular orbits and coupling degree,which results in difference in electronic transport.

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Filtering Features of Solid-Fluid Rectangular Doping Phononic Crystals LIU Qineng 2011, 28(2): 301-305.  Abstract ( )   PDF (336KB) ( )   Mode condition of elastic wave in solid-fluid rectangular doping phononic crystals is obtained with restriction conditions of elastic wave.Response of defect mode to mode quantum number and length of rectangle are calculated.Multichannel filters are realizated with relationship of defect mode and mode quantum number.Harmonious filters are obtained as defect mode varies with mode length of rectangle.

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Simulation and Fabrication of High-Voltage 4H-SiC PiN Diode with JTE ZHANG Fasheng, ZHANG Yuming 2011, 28(2): 306-312.  Abstract ( )   PDF (303KB) ( )   Reverse voltage characterizations of 4H-SiC PiN diodes with junction termination extension(JTE) are simulated by using a two-dimensional device simulator(ISE-TCAD 10).0.4H-SiC PiN diodes with JTE are fabricated with a planar fabrication process based on simulation.Good consistency between simulation and experiments was achieved.It shows that a 4H-SiC PiN diode with optimized JTE edge termination can reach a breakdown voltage of 1600 V,which is more than 90 percent of ideal parallel plane junction breakdown voltage.

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A Cascading Failure Model for Power Systemes ZHOU Haiping, CAI Shaohong 2011, 28(2): 313-316.  Abstract ( )   PDF (237KB) ( )   A failure cascading model for power systemes is proposed,in which energy dissipation and capability expansion are considered.Simulations are performed on both regular grids and scale-free networks.Self-organized critical phenomenon is observed in both cases.It means that energy dissipation and capability expansion are important factors in self-organized critical status.In addition,it shows that the maximum size of cascading failures in scale-free networks is much larger than that in regular networks.