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25 July 2010, Volume 27 Issue 4 Previous Issue    Next Issue

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Conservative Parallel Schemes for Diffusion Equations YUAN Guangwei, HANG Xudeng 2010, 27(4): 475-491.  Abstract ( )   PDF (916KB) ( )   In numerical simulation of radiation hydrodynamics problems,diffusion computation costs most part of simulation time.It is urgent to construct parallel schemes which are conservative,of high precision and unconditionally stable.The aim of the paper is to devise conservative parallel schemes based on methods of "prediction and/or correction" for nonlinear diffusion equations.Numerical results are presented to examine performance of conservative parallel schemes,such as accuracy,stability and parallel speedup.

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Adaptive Discontinuous Galerkin Method for Euler Equations WU Di, YU Xijun 2010, 27(4): 492-500.  Abstract ( )   PDF (485KB) ( )   We combine Runge-Kutta discontinuous finite element method(RKDG) with adaptive method to solve Euler equations.Domain is divided into unstructured tetrahedral meshes.Local mesh refinement technique is used.According to changes in numerical solution,mesh is refined or coarsened locally.Therefore,number of overall grids is reduced and computational efficiency is increased.We give four different adaptive strategies and analyze advantages and disadvantages.Finally,several examples validate the method.

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Improvements on Definition of Interficial Riemann Problem in Real Ghost Fluid Method DING Yan, YUAN Li 2010, 27(4): 501-508.  Abstract ( )   PDF (392KB) ( )   In conventional ghost fluid method,Riemann problems are defined by taking direatly states at grid points as initial conditions.In this article,we improve this approach by taking states at interpolated points as initial conditions.States at interpolated points are obtained by area average of states at four surrounding grid points.Since initial conditions are smooth,our method gives results with less numerical oscillations.Numerical experiments illustrate that the method is effective.

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Runge-Kutta Discontinuous Galerkin Method for Detonation Waves ZHANG Lei, YUAN Li 2010, 27(4): 509-517.  Abstract ( )   PDF (633KB) ( )   A Runge-Kutta discontinuous Galerkin(RKDG) method for conservation law with source term is shown.The method is implemented with Strang split or unsplit methods,and is applied to solve one-dimensional conservation law with source term as well as one and two-dimensional detonation wave problems.In order to compare with the fifth-order finite volume WENO method,a special reconstruction method is proposd to calculate integration of the source term with high-order spatial accuracy.Numerical tests in one dimension show that the RKDG method has smaller errors than WENO method for nonstiff problems and is more accurate in capturing position of discontinuity in stiff problems.Numerical simulations of detonation waves demonstrate that the RKDG method is more effcient in resolving detailed structure of detonation waves and location of detonation front.

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Turbulent Particle Dispersion Modeling with PDF Equation Based on Langevin Equation of Fluid Velocity XU Jiangrong, ZHANG Ping, CHEN Jiangxing, DING Ning 2010, 27(4): 518-526.  Abstract ( )   PDF (342KB) ( )   A Langevin equation of fluctuating velocity of fluid ‘seen’ by particle is simplified in Minier's model.Autocorrelation of turbulence fluctuating velocity is obtained,which has non-isotropic property.Corresponding PDF model of particle is obtained and a simplified form is used to predict turbulent particle dispersion in grid-generating turbulence flow.PDF model is solved analytically and solutions are compared with experimental results of Wells and Stock.

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An Efficient Lagrange Point Tracking Algorithm for Fixed Grids LIU Yongfeng, MING Pingjian, ZHANG Wenping, ZHU Minggang, NI Daming 2010, 27(4): 527-532.  Abstract ( )   PDF (311KB) ( )   An improved particle tracking algorithm based on unstructured grids and hybrid grids with arbitrary polygon faces is presented.A dummy triangulation of non-planar polygon faces is carried out as tracking particles across arbitrary hybrid cell faces.Feasibility and reliability are shown through numerical examples.cpu time of the algorithm is compared with that of two algorithms introduced by Haselbacher et al for particles spray into a fixed chamber.The speed up can reach as high as 47% for 10000 particle tracking.

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A Two-dimensional Cylindric Symmetric Radiative Transfer Benchmark Model and Code Tests YANG Rong, HANG Xudeng, LI Jinghong 2010, 27(4): 533-540.  Abstract ( )   PDF (386KB) ( )   A series of exact solutions are constructed for two-dimensional radiative transfer and radiative diffusion problems with outer source.These solutions exhibt physical characteristics with simple expressions.Moreover,transport solutions degenerate directly into solutions of corresponding diffusion equations.Test results of the diffusion model with LARED-R are presented and analyzed.

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Generalized Coarse-mesh Finite Difference Acceleration for Method of Characteristics in Unstructured Meshes CHAI Xiaoming, YAO Dong, WANG Kan, YU Yingrui, WANG Liangzi 2010, 27(4): 541-547.  Abstract ( )   PDF (413KB) ( )   Generalized coarse-mesh finite difference(GCMFD) method,which uses generalized-geometry coarse meshes to speed up the method of characteristics(MOC),is proposed.A method adjusting width factor automatically is adopted in the GCMFD method.The GCMFD method is adopted in a 3-D neutron transport MOC code TCM.Numerical tests are used to verify acceleration effect of GCMFD in TCM.It shows that the GCMFD method can use generalized-geometry coarse meshes to accelerate MOC iteration,and the GCMFD method with automatically adjusting width factor has good acceleration effect.

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Implementation of Particle-Mesh Ewald(PME) on Graphics Processing Units XU Ji, GE Wei, REN Ying, LI Jinghai 2010, 27(4): 548-554.  Abstract ( )   PDF (372KB) ( )   In this article,long range part of electrostatic interaction is accelerated using GPUs in NIVIDIA CUDA programming environment.Particle Mesh Ewald algorithm is adopted and split into 5 procedures:parameters designation,discretization of point charges into grids,Fourier transformation of grids,potential of electrostatic interaction,and force calculation of electrostatic interaction.The codes are tested by seven biomolecular systems with different sizes.Roughly 7-fold speedup over one core of mainstream CPUs is obtained.The codes can be integrated into molecular dynamic simulation software packages that already exst or used as part of GPU codes developed in the future to further speedup traditional MD simulations.

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Numerical Analysis on Flow Field and Dynamic Characteristic of a Pitching Blunt Body ZHAO Haiyang, LIU Wei 2010, 27(4): 555-560.  Abstract ( )   PDF (353KB) ( )   Flowfield around a blunt body at transonic speed is simulated numerically.It indicates that plentiful flowfield structures behind the blunt body determine base pressure distribution.Numerical simulation of free pitch oscillation shows that limited cycle oscillation is observed as a result of dynamic instability in transonic regime.During a free pitch oscillation,front part blunt body conducts work to the flow field which releases blunt body energy and inhibits swing.The rear part of the blunt body gains energy from the flow field which increases the blunt body energy and the motion is considered unstable.As energy of the front blunt body and the rear body is equal,the capsule falls into a limited cycle oscillation.

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Thermal Conductivity Inversion with Adjoint Equation Method TANG Zhonghua, QIAN Weiqi, LIU Yongli 2010, 27(4): 561-566.  Abstract ( )   PDF (397KB) ( )   A typical inverse heat conduction problem(IHCP) is converted to an optimization problem.An inversion algorithm of adjoint equation method(AEM) is developed.In order to treat ill-posedness of IHCP,a stop criteria used in iterative regularization method is employed.In a typical case,the inversion method of AEM is feasible and not very sensitive to measurement noise as noise level is relatively low.As measurement noise presents,difference between estimated thermal conductivities and exact values at boundaries x=0 and x=L is significant,which is due to the fact that gradient of objective function with respect to the change of thermal conductivity at boundaries is relatively small.Moreover,further research shows that as noise level rises,significant difference between estimated and exact values of thermal conductivity presents and initial value has great influence on estimated values.

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Semi-analytical Integration for Coefficients of Charge on Plane Elements in Surface Charge Method ZHANG Yifei, ZHANG Zhiquan, CHEN Yuefeng 2010, 27(4): 567-572.  Abstract ( )   PDF (250KB) ( )   A complete analytical method for coefficient of charge on plane elements in SCM(surface charge method) is complicated under linear or high order charge density approximation.A kind of semi-analytical integration is proposed.It transforms the integral under local reference into a separable double integration under global reference.Since the inner layer integration is analytical,the original integration can be simplified to a one-dimensional problem which can be calculated by traditional numerical method.As for singular integral,eliminating singularity technique by adding auxiliary function is adopted.It indicates that high precision is achieved and the method is applicable.

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Antenna EMC Analysis with Hybrid PO-TDIE Algorithm QIN Yujian, REN Meng, LI Ying, ZHOU Dongming, HE Jianguo 2010, 27(4): 573-578.  Abstract ( )   PDF (289KB) ( )   A hybrid method of physical optics and time domain integral equation(PO-TDIE) is presented to analyze antenna electromagnetic compatibility(EMC) on electrically large platform.General formulation and computational complexity are deduced in detail.Numerical results show that the computational cost is reduced obviously compared with classical marching-on in time(MOT) solver.The hybrid method could be effectively applied in EMC analysis.

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Vibrational Energy Relaxation of Nitromethane in Collective Model ZHAO Bo, CUI Jiping, FAN Jing 2010, 27(4): 579-585.  Abstract ( )   PDF (424KB) ( )   We study vibrational energy relaxation of a "doorway model" (including the scissor,wagging and rocking mode) for nitromethane by molecular dynamics in collective interaction model.Relaxation time in vibrational cooling(VC) process agrees with experimental results.Frequency shifts for modes are consistent with experimental measurements at high-pressure in vibrational pumping(VP) process.VP process of nitromethane is observed in MD simulation in detail.It is shown that collective effects are important in vibrational energy relaxation at high-pressure and high-temperature,and energy of overtone-frequency as well as fundamental frequency of the modes must be taken into account in translational-vibrational energy transfer.

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3D Crack Propagation in Cohesive Zone Models ZHANG Zhichun, QIANG Hongfu, ZHOU Wei 2010, 27(4): 586-592.  Abstract ( )   PDF (342KB) ( )   A cohesive zone model is employed in finite element formulation using nonlinear explicit dynamic algorithm.A 4-node tetrahedron element and a 6-node triangular prism element are chosen as volumetric and cohesive stress/displacement element,respectively.A bilinear constitutive equation is used to describe cohesive tractions and displacement jumps.Interfacial penetration of adjacent layers after complete rupture is avoided.A damage criterion is formulated in displacement jump space.The final displacement jump is calculated with Benzeggagh-Kenane's propagation criterion.The onset displacement jump is calculated with Turon's initial damage surface criterion.The code(CVFEM) can simulate material interface delamination under mixed-mode ratio loading in 3D.Three examples are shown.Numerical predictions are compared with those obtained by Abaqus 6.7.

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Light Extinction of Randomly Oriented Smoke Screen with Clustered Agglomerates LEI Chengxin, WU Zhensen 2010, 27(4): 593-597.  Abstract ( )   PDF (283KB) ( )   Monte Carlo method is used to study light extinction of smoke screen with clustered agglomerates consisting of spherical primary particles in a cluster-cluster aggregation(CCA) model.Extinction factor and absorption factor of randomly oriented smoke screen with clustered agglomerates are calculated with discrete dipole approximation(DDA).It shows that exinction properties are determined by radius and number of primitive particles besides refractive index and extinction properties can be decreased by aggregation.At a given primitive particle number,maximum extinction is obtained with optimum radius of primitive particles.

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Nematic Liquid Crystal Cell with Bend Distortions Based on Modified Gruhn-Hess Pair Potential ZHOU Xuan, ZHANG Zhidong 2010, 27(4): 598-602.  Abstract ( )   PDF (208KB) ( )   Nematic liquid crystal cell with bend distortions is studied in a modified Gruhn-Hess spatially anisotropic pair potential model.Under one-constant approximation,we get continuous form of free energy density formula in a perfect order considering second rank distortions,which is consistent with elastic theory.Strong anchoring nematic liquid crystal cell with bend distortions in the model doesn't show surface discontinuities as in the elastic theory.With Monte Carlo simulation,we find that the k13 term in pair potential increases the fluctuation in the middle cell.

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Mode and Bandgap of Elastic Wave in Solid-Liquid Cylindrical Phononic Crystal LIU Qineng 2010, 27(4): 603-607.  Abstract ( )   PDF (256KB) ( )   Mode of elastic wave in 1D solid-liquid cylindrical phononic crystal is obtained with restriction conditions of elastic wave.Bandgap of elastic wave is calculated with dispersion function.New structure of bandgap in 1D solid-liquid cylindrical phononic crystal is revealed.Bandgap of 1D solid-liquid cylindrical phononic crystal is determined with quantum number of mode and cylindrical radius.

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Morphology of Magnetic Fractal Clusters on Triangular Lattice WU Yiqi, XU Xiaojun 2010, 27(4): 608-612.  Abstract ( )   PDF (306KB) ( )   In a diffusion-limited aggregation model with spin freedom in each particle,morphology and fractal dimension Df of magnetic clusters grown on two-dimensional triangular lattices are investigated with Monte Carlo study.Power-law interaction J/ra is used.It shows that as α≥5 patterns of clusters hardly vary with J.Their fractal dimensions range from 1.50 to 1.70.With decreasing α,morphology evolution of clusters exhibits rich behaviors.Fractal dimension Df changes continuously from about 1.20 to 1.90.

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Magnetic Properties of One-dimensional Antiferromagnetic Ising Diamond Chain FENG Liya, XIN Zihua, WANG Wutao 2010, 27(4): 613-618.  Abstract ( )   PDF (319KB) ( )   Monte Carlo method is used to study magnetic properties of S=1/2 one-dimensional antiferromagnetic Ising diamond chain.In this system,due to antiferromagnetic interactions and trigonal structure,there exists spin frustration.The magnetic behaviors and spin configurations of the system are investigated with different antiferromagnetic interactions.Magnetization plateaus at M=MS/3 are obtained in process of magnetization.Width of plateau exhibits variously for different antiferromangnetic interactions.Spin configurations are presented in the magnetization process as there appears the M=MS/3 plateau and the system lies in a metastable state.Consequently,conditions in which the metastable state appears are concluded.In addition,hysteresis loops of the system are studied in different temperatures.With increase of temperature the hysteresis loops become more and more unobvious,and finally disappear.

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Electrode Configurations and Coupling Modes in Organic Molecular Electronic Transport LIU Ruijin 2010, 27(4): 619-623.  Abstract ( )   PDF (261KB) ( )   With ab initio theory and elastic scattering Green's function method,electronic transport of organic molecule 1,4-phenylene diisocyanide is investigated with two electrode configurations and coupling modes.Coupling properties,electronic transport spectrums,positions of turning-on voltage,distributions of conductance platform,and responses of current with different configurations and couplings are studied.Coupling coefficients,height of conductance platform and current can be affected by changing the distance between two electrodes.

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Improved Ant Colony Optimization Algorithms for Ground State Energy of Quantum Mechanical Systems CHEN Xia, TANG Chen 2010, 27(4): 624-632.  Abstract ( )   PDF (390KB) ( )   Ant colony optimization(ACO),a global optimization method,is proposed to analyze ground state energy of quantum mechanical systems.It simulates the way that real ants find a shortest path from nest to food source and back.In order to reduce iterations and improve solutions,ACO algorithm for ground state energy is modified.The proposed method exhibits advantage compared with traditional variation method.Ground state energy of helium atom and hydrogenic donors in GaAs-(Ga,Al)As quantum dot are calculated.The algorithm is demonstrated via comparison with variational method and genetic algorithms (GAs).