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25 March 2009, Volume 26 Issue 2 Previous Issue    Next Issue

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Adaptive Discontinuous Galerkin Methods for Hyperbolic Conservation Laws XU Yun, YU Xijun 2009, 26(2): 159-168.  Abstract ( )   PDF (980KB) ( )   For systems of nonlinear hyperbolic conservation laws,two adaptive discontinuous Galerkin finite element methods(ADGM) generating conforming unstructured triangular meshes are proposed.The first one is for structured mesh. It is simple and fast.The second one is for both structured and unstructured meshes.Based on posteriori error estimation of nonlinear hyperbolic conservation laws,a discontinuous interfacial mesh refinement indicator is shown in generating adaptive meshes. It is shown that the methods are flexible and reliable. Computation cost is decreased.

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Anti-reversal Finite Element for Soft Tissue Modeling ZHANG Qiukui, LUO Limin 2009, 26(2): 169-174.  Abstract ( )   PDF (370KB) ( )   An anti-reversal FEM model is proposed.A relationship between compression ratio and pressure within compressed element is introduced in the constitutional equation. In the model elastic energy of an element is a polynomial function of nodal displacement.It simplifies evaluation in the conjugate gradient method and improves efficiency.It shows that the method is applicable to real-time simulation of soft tissues under large deformation.

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Symmetry-preserving Finite Volume Element Scheme on Unstructured Quadrilateral Grids NIE Cunyun, SHU Shi, SHENG Zhiqiang 2009, 26(2): 175-183.  Abstract ( )   PDF (389KB) ( )   With special control volumes and finite volume element spaces,two symmetry-preserving finite volume element schemes for stationary diffusion problems are established on unstructured quadrilateral grids.Saturated order of error in L2-norm and H1-norm for discrete solutions under quasi-uniform partition is demonstrated as diffusion coefficient is smooth.Numerical examples verify theoretical results.It shows strong adaptability of the scheme on distorted quadrilateral grids and for diffusion problems with non-smooth coefficient.The second scheme shows super-approximation for flux function at central point of element as grids are orthogonal.

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One-dimensional Load Balancing Method with Memory Constraint LIU Xu, MO geyao, CAO Xiaolin 2009, 26(2): 184-190.  Abstract ( )   PDF (369KB) ( )   A one-dimensional load balancing method is proposed with memory constraint.It is an iterative method which converges to optimal partitioning linearly.Experiments on(1 024) CPUs with typical load imbalance models and a three-dimensional molecular dynamics program show effectiveness of the method.

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Parallel Incomplete Factorization Preconditioning of Block Tridiagonal Linear Systems with 2-D Domain Decomposition WU Jianping, SONG Junqiang, ZHANG Weimin, LI Xiaomei 2009, 26(2): 191-199.  Abstract ( )   PDF (447KB) ( )   Based on two-dimensional domain decomposition with small overlapping,we provide a method in which local lower and upper triangular incomplete factors are combined into an effective approximation for global incomplete lower and upper triangular factors of coefficient matrix.Parallelization method is applicable to any preconditioner of incomplete type. Parallel performance metric of two-dimensional parallel preconditioner is compared to that of one-dimensional ones.Experiments show that it is more efficient than additive Schwarz technique and two-dimensional decomposition is better than corresponding one-dimensional decomposition as more processors are used for parallel computation.

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Numerical Simulation of Flow Field with Moving and Deforming Objects DENG Shusheng, GENG Jihui, YE Jingfang, TAN Junjie 2009, 26(2): 200-210.  Abstract ( )   PDF (1003KB) ( )   Infiltration of blast waves in a structure with limited opening in the front wall is investigated numerically.Numerical methods deal with generation of moving and deforming unstructured mesh,moving boundary condition and topological change of geometry are used to blast-structure interactions.Movements of door located at the opening,collision of door with a baffle,fracture of door and displacement of fragment are considered.It is concluded that the methods are suitable to deal with blast-structure interaction.

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High-order CE/SE Method and Applications ZHANG Deliang, WANG Jingtao, WANG Gang 2009, 26(2): 211-220.  Abstract ( )   PDF (724KB) ( )   Space-time conservation element and solution element(CE/SE) method with second order accuracy is modified on hexahedral grids. High-order accuracy in space and time is obtained by expanding variables in SEs with high order.CE/SE method is used to capture shock waves in chemical reaction flows,elastic-plastic flows and unsteady multi-phase incompressible flows.Numerical results are compared with experimental and theoretical results of classical examples.It is indicated that the method is easy to implement, accurate and efficient.Application of high order CE/SE method is extended.

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Study on Supersonic Base Flow Using RANS/LES Methods XIAO Zhixiang, FU Song 2009, 26(2): 221-230.  Abstract ( )   PDF (639KB) ( )   RANS/LES hybrid methods are developed on the basis of shear stress transport and weakly nonlinear k-ω models with compressible corrections.Supersonic flowfields behind a cylindrical afterbody are investigated to explore rich flow structures and aerodynamic characteristics.Compressible correction shows good agreement with experiment.Results by hybrid methods present detailed and reasonable flow structures,turbulence information and unsteady characteristics.

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Aerodynamic Investigation of a 2D Wing and Flows in Ground Effect YANG Wei, YANG Zhigang 2009, 26(2): 231-240.  Abstract ( )   PDF (599KB) ( )   A numerical investigation is performed to study aerodynamics of a 2D NACA0012 wing and flows in ground effect (IGE). Lift and drag forces are obtained and pressure distribution on airfoil surfaces is recorded at different angles of attack and ground clearances. Viscous flow near ground and air compressibility are taken into account. High lift is obtained as the airfoil is in dose proximity to the ground. The stall angle decreases with reduction of the ground clearance, due to higher adverse pressure gradient. Viscous effect of floor shows less effect on airfoil. Compressibility should be taken into account at lower ground clearances.

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One-dimensional Numerical Simulation of Cl2/BHP Droplet Chemical Reaction Flows XUE Shesheng, LIU Quan, LI Shouxian, SHU Xiaojian 2009, 26(2): 241-246.  Abstract ( )   PDF (282KB) ( )   To investigate mechanism in TUDOG(Transeverse Uniform Droplet Oxygen Generator),a one-dimensional chemical reactive flow model is established to describe physical and chemical performance as mixed Cl2/He gases passing through BHP(KOH,H2O2,H2O)droplet field transeversely.Gas-phase flowfield is approximately considered as 1-D homogeneous flow according to incompressibility hypothesis.Chemical reaction in liquid droplet is described by reactive-diffusion equations with 4 gasous components.Concentration of gasous components are described with convective-diffusive equations. Droplets are gasous source or sink. It is shown that chlorine utility,singlet oxygen yield and generator efficiency are close to experiment results.The model is verified in simulating interactions between mixing gases and BHP droplets.

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Two-dimensional Simulation of Strong-coupled Radiative Transfer LI Shuanggui, HANG Xudeng, LI Jinghong 2009, 26(2): 247-253.  Abstract ( )   PDF (428KB) ( )   Strong-coupled multigroup radiative transfer in optically thick regions are analyzed.A simple conner balance method in 2D is presented.A grey transport acceleration scheme is generalized to accelerate source iteration convergence of differenced multigroup transport equations.

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Atomic Orbital Close-coupling Calculations of Charge Transfer in He2+-H- Collisions YAN Shijie, LIU Ling, WANG Jianguo 2009, 26(2): 254-260.  Abstract ( )   PDF (374KB) ( )   Charge transfer in He+-H- collisions is investigated using two-center atomic orbital close-coupling(TC-AOCC) method.All bound states of He+ (nl) with n≤7,as well as 1s bound states and ns(n=2~6) quasi-continuum states of H- are included in the AOCC basis.Energies of bound states calculated are in good agreement with NIST data and theoretical results.The total and state-selective cross sections are calculated within a range of energy from 4 to 400 keV.For low-energy collisions,dominant capturing channels are those with quantum numbers n=3-5.With increasing incident energies,transfer of charge to n=2 becomes the dominant reaction.Moreover,for low-energy collisions,cross sections for electrons capture to higher-l states are bigger than that to lower l states.For high-energy collisions,dominant channel is to l=1 states.Charge exchange spectrum due to electron captured to excited states is calculated.Importance of cascade effects is found.

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Deconvolution of Electron Energy Loss Spectrum of Diatomic Molecules LIU Wenjing, ZHU Linfan, GE Min, XU Kezun 2009, 26(2): 261-266.  Abstract ( )   PDF (323KB) ( )   A deconvolution method for electron energy loss spectrum of diatomic molecules is proposed.Fitted energy positions are locked on accurate spectroscopic data.Calculated Franck-Condon factors are adjusted by a quadratic function.Precision requirement for Franck-Condon factors is reduced.Undermined parameters in deconvolution procedure are reduced dramatically.Precision of fitted results is improved. Optimized algorithm in fitting procedure avoids a lot of integral calculations.The program is used to deconvolve electron energy loss spectrum of H_2.Vibrationally resolved optical oscillator strengths are determined.The results agree well with previous experimental and theoretical studies.

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Radiative Entropy Transfer Equation and Numerical Computation of Radiative Entropy Generation in Semitransparent Graded Index Medium LIU Linhua 2009, 26(2): 267-274.  Abstract ( )   PDF (360KB) ( )   With hypothesis that radiation is incoherent, based on Planek's definition of radiative entropy, radiative entropy transfer equation and local radiative entropy generation in semitransparent graded index medium are derived. A calculation method based on discrete-ordinates approach is used to solve radiative entropy transfer equation in semitransparent graded index medium. A one-dimensional slab system filled with semitransparent graded index medium is taken as an example to verify the radiative entropy transfer equation and the calculation method. Numerical results of dimensionless radiative entropy generation of the slab system agree well with entire thermodynamics analysis.

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Effect of Groove Angle on Ejecting Mass LIU Chao, QIN Chengsen, FENG Qijing, WANG Pei 2009, 26(2): 275-280.  Abstract ( )   PDF (306KB) ( )   A two-dimensional elastic and plastic hydrodynamics Eulerian code MEPH is applied to simulate aluminium ejecting with single defect.We focus on change of maximum ejecting velocity and ejecting factor with different angle and shape.Numerical results are consistent with experiments.

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Compression of BN Nanotubes: A Molecular Dynamics Study JING Yuhang, MENG Qingyuan 2009, 26(2): 281-286.  Abstract ( )   PDF (383KB) ( )   With molecular dynamics(MD) method,axial compression of both perfect and defective armchair(7,7) single-walled BN nanotubes is simulated.Tersoff potential is used to simulate interaction among atoms.To verify the method,armchair(7,7) single-walled carbon nanotubes are calculated.It shows that compressive failure mode of BN nanotubes is almost the same of carbon nanotubes,in which locally-buckling on walls are observed.It is revealed that compressive strength of nanotubes,such as critical axial load,is related to applied strain rate and is affected by temperature especially at low temperatures.However,elastic deformation of nanotubes is not affected by strain rate.It is found that vacancy defects are quite harmful to mechanical properties.Compared with perfect nanotubes,compressive axial strength of defective nanotubes is not affected by temperature significantly.

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Anomalous Dynamic Scaling in 1+1 Dimensional Wolf-Villain Model XUN Zhipeng, TANG Gang, HAN Kui, XIA Hui, HAO Dapeng, ZHOU Wei, YANG Xiquan 2009, 26(2): 287-292.  Abstract ( )   PDF (345KB) ( )   1+1 dimensional Wolf-Villain model for molecular-beam epitaxy(MBE) growth is investigated with kinetic Monte-Carlo simulation in large scale and during long growth time so that crossover effects are eliminated.Global and local dynamic exponents are obtained.It is shown that Wolf-Villain model in 1+1 dimensions exhibits intrinsic anomalous scaling behavior in time and length simulated.The result is inconsistent with theoretical analysis by López.

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Slowing Diffusion with Coupling of Random Walkers LI Muzi, YAN Jianhua, QI Xiaohua 2009, 26(2): 293-298.  Abstract ( )   PDF (286KB) ( )   A model of coupling discrete Markovian random walkers is studied. A pair of walkers are coupled. The distribution of arguments is updated to have higher probability pointing to its conjugate walker in each step. Increasing coupling strength slows down diffusion. Stochastic distribution of arguments rather than lengths dominates in this issue. Due to coupling, a pair of walkers arrive at some synchrony state. In some sense, it is the synchrony that induces diffusion slowing.

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Radial Basis Functions and Coupled Method in Computational Electromagnetics ZHANG Huaiqing, YU Jihui, ZHENG Yali 2009, 26(2): 299-310.  Abstract ( )   PDF (660KB) ( )   For boundary conditions with functions changing rapidly,especially in charged conductors,we combine compact feature of wavelet functions and high accuracy of RBF in a coupled method and solve ground metal trough/box problems. Rectangular,ridge and round waveguides are analyzed with RBF and FEM methods.Numerical experiments show that RBF method is efficient in solving electromagnetic boundary and eigenvalue problems.RBF method is easier and more accurate with less nodes.

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Artificial Neural Network Prediction of Crosstalk Coupling Between Interconnecting Wires LI Xu, YU Jihui, LI Yongming, WANG Quandi 2009, 26(2): 311-316.  Abstract ( )   PDF (305KB) ( )   A method predicting crosstalk coupling between interconnecting wires with artificial neural networks is proposed.Parameters that influence crosstalk coupling are selected as input prediction factors.Back propagation neural network constructs a mapping relation between input prediction factors and output crosstalk coupling of interconnecting wires.Learning sample sets computed by MTL and FDTD method are used to train BP networks.A prediction BP model is obtained.BP predictions and test sample results are compared.