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25 May 2011, Volume 28 Issue 3 Previous Issue    Next Issue

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Self-adaptive Method for Energy Deposition of Photons and Electrons QIU Youheng, YING Yangjun, WANG Min, CHEN Xingliang 2011, 28(3): 317-322.  Abstract ( )   PDF (338KB) ( )   A method is proposed for choosing electron cutoff energy,which is self-adaptive with cell size,background material and electron position.As residuary range of an electron defined by total stopping power is less than distance to the nearest cell boundary,the electron is killed.Compared with the CUT model used in MCNP program,efficiency and precision of self-adaptation method is higher.The most important is that cutoff energy of electron is selected automatically in program in all models,without consideration of energy of particles or dimension of model.

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High Efficiency Monte Carlo Sample Method for Super-high Energy Neutrons LI Shu, TIAN Dongfeng, DENG Li 2011, 28(3): 323-328.  Abstract ( )   PDF (309KB) ( )   An adding weight sample method is developed for neutron transportation in inertial confinement fusion.It aims to increase samples in important zone and decrease samples in non-important zone.Weight of each sample is corrected for keeping calculated results non-bias.Typical model is simulated.It indicates that the method improves effectively neutron samples in fusion zone,while collisions between neutrons increase obviously.Calculation error of super-high energy neutron flux is decreased remarkably.Calculation efficiency of super-high energy neutrons is improved.

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One-dimensional Simulation of RF CH_4 Plasma in a Fluid Model LV Shaobo, LIN Zeng, BA Dechun, WANG Qing 2011, 28(3): 329-340.  Abstract ( )   PDF (717KB) ( )   A one-dimensional fluid model for RF methane plasma is presented.Equations of particle balance with drift-diffusion approximation for fluxes,and electron energy balance are solved.Totally 20 species(neutrals,radicals,ions,and electrons) are included in the model,as well as 49 reactions(27 electron reactions,7 ion-neutral reactions,and 15 neutral-neutral reactions).It is found that high electron reaction-rate occurs at high electric-field region.Besides inlet gas CH4,neutral gases H2,C2H6,C3H8,C2H4,and C2H2 also show high densities in the plasma.The main radical in plasma is CH3,with a density of about 1019m-3.At low pressures(e.g.,18Pa) the most important ion is CH5+.At high pressures(e.g.,67Pa) C2H5+ becomes the dominant ion.Radical and ion fluxes towards electrode(except C2H5+) increase slightly with power.

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A Parallel Contact Detection Algorithm for Explicit Finite Element Analysis BAI Xiaoyong, HE Yingbo, CHEN Chengjun 2011, 28(3): 341-346.  Abstract ( )   PDF (289KB) ( )   A parallel contact detection algorithm for explicit finite element analysis is introduced.A parallel bucket sort algorithm is developed with domain decomposition and message passing.Contacts can occur between surfaces that own by two arbitrary computational nodes.Potential contact pairs are sorted into three categories according to communication requirements.It is shown that the parallel algorithm achieves high speedup and efficiency.

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Numerical Simulation of Viscous Incompressible Flow with Variational Multiscale Method ZHU Haitao, OUYANG Jie, WANG Xiaodong 2011, 28(3): 347-354.  Abstract ( )   PDF (774KB) ( )   Velocity filed is decomposed into "coarse" and "fine" scales with a variational mulitiscale method.The "fine" scale is modeled by bubble functions,and solved with Petrov-Galerkin method.A stabilized term and stabilization parameter are introduced by coupling the "fine" and "coarse" scales.A variational multiscale equation which preserves properties of both "fine" and "coarse" scales is solved with a finite element method.It shows that the method is stable and accurate.It eliminates spurious oscillations caused by dominated advection term and uncoupling between velocity and pressure in numerical simulation of incompressible flows.The stabilization parameter can be applied to structure and unstructure meshes as well.

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Lattice Boltzmann Simulation of Gas-Solid Flow in a Driven Cavity CAI Xintao, GUO Zhaoli, ZHENG Lin, ZHENG Chuguang 2011, 28(3): 355-360.  Abstract ( )   PDF (365KB) ( )   We present an extension of lattice-Boltzmann-lattice-gas method proposed by Masselot and Chopard for gas-solid flows,in which the drag force between gas and solid is considered.The method is applied to particles in a driven cavity flow.Effects of Stokers number and total number of particles are analyzed.Simulation results are compared with previous works.It shows that the proposed LBE-LGA method can serve as a promising tool for simulating gas-particle flows.

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Lattice Boltzmann Method for Heat Transfer in Melting with Natural Convection GAO Dongyan, CHEN Zhenqian 2011, 28(3): 361-367.  Abstract ( )   PDF (383KB) ( )   A lattice Boltzmann model is developed to simulate melting with natural convection.In a lattice Boltzmann model for non-linear convection diffusion equations,an evolution equation of temperature distribution is constructed with selecting an equilibrium distribution function and a nonlinear source term properly.Thermal properties of solid phase and liquid phase are accomplished by using an adjustable relaxation time.Simulation results agree well with analytical solution and correlation in previous studies.It indicates that natural convection has importanct influence on total heat transfer,and heat conduction of solid phase affects total heat transfer,melting velocity and temperature distribution.

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A Modified PUFF Equation of State for Anisotropic Materials HUANG Xia, TANG Wenhui, JIANG Banghai, WANG Daorong 2011, 28(3): 368-374.  Abstract ( )   PDF (348KB) ( )   A modified PUFF equation of state is proposed with considenation of both non-linear volume change and anisotropic strength of material under compression and dilation.Taking 2-D impact of orthotropic material and thermal shock wave under X-ray radiation as examples,a finite element program is developed.The mean stresses obtained by traditional and modified PUFF equation of state are compared.They are obviously different at low compression and tension states.With increase of stress,they tends to be consistent gradually.

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A modified PUFF equation of state is proposed with considenation of both non-linear volume change and anisotropic strength of material under compression and dilation.Taking 2-D impact of orthotropic material and thermal shock wave under X-ray radiation as examples,a finite element program is developed.The mean stresses obtained by traditional and modified PUFF equation of state are compared.They are obviously different at low compression and tension states.With increase of stress,they tends to be consistent gradually. QIANG Hongfu, CHEN Fuzhen, GAO Weiran 2011, 28(3): 375-384.  Abstract ( )   PDF (745KB) ( )   Modified equations for surface tension are derived by modifying normal and curvature with corrected smoothed particle method(CSPM).It is based on smoothed particle hydrodynamics(SPH) method with surface tension proposed by Morris.Both Morris and our method are tested via a semicircular problem.Factors that affect accuracy are investigated including surface definition,normal and curvature calculation.Smoothed length in curvature calculation is also confirmed reasonable.Furthermore,formation of a liquid drop with initial square shape under surface tension is simulated.Compared with Morris method and grid-based volume of fluid method,it is proved that the accuracy of our method is higher and particle distribution is more homogeneous.Finally,coalescence process of two oil drops in water under surface tension is simulated.

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A Study on Heavy Oil Well Test DU Dianfa, LI Dongdong, SHI Dayou, XU Tao 2011, 28(3): 385-396.  Abstract ( )   PDF (419KB) ( )   Nine kinds of heavy oil thermal recovery models are summarized,including non-Newtonian power-law fiuids model,two-region composite reservoir model,three-region composite reservoir model,multi-region composite reservoir model,model with consideration of gravity override and interference testing well model,etc.Pressures and pressure derivatives are briefly analyzed.Advantages and disadvantages of models are compared.Problems in current models and trends in research of heavy oil well test are pointed out.

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Boundary Element Analysis of Thin-walled Structures in Elasticity Problems with Exact Geometrical Representation GU Yan, ZHANG Yaoming, LI Gongsheng 2011, 28(3): 397-403.  Abstract ( )   PDF (381KB) ( )   An exact geometrical representation,arc element,is introduced for thin bodies with circular boundary.A general nonlinear transformation available for arc elements is constructed.With exact geometrical representation,numerical accuracy of nearly singular integrals is greatly improved,which makes possible to deal with ultra-thin structures.

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First-order Velocity-Stress Elastic Wave Field Separation Scheme for Biot Two-phase Isotropic Medium CHEN Keyang 2011, 28(3): 404-412.  Abstract ( )   PDF (758KB) ( )   We propose an equivalent first-order hyperbolic velocity-stress Biot two-phase isotropic medium elastic wave equation in order to separate pure fast and slow compress waves and pure shear wave in full wave field of two-phase medium.Feasibility of the method is demonstrated with divergence and curl theory.In a high-order staggered-grid finite-difference scheme forward simulating operator is constructed.PML absorbing boundary condition and stability condition are derived.Isotropic and heterogeneous layered two-phase medium models are tested.Full elastic wave field,completely separated pure compress wave and pure shear wave of the solid fluid phase components are obtained.Boundary absorbing effect is perfect,and numerical precision is high.It shows that the fast compress wave and slow compress wave are coupled which can't be separated.They belong to pure compress wave fields.Energy of slow compress wave in fluid phase is greater than that in solid phase which is important in understanding propagating laws and validating elastic wave theory for two-phase medium.

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Unified Modeling and Optimization of UPML Absorbing Boundary Conditions CHAI Yanjie, SUN Jiyin, LI Linlin, SUN Dongyang 2011, 28(3): 413-419.  Abstract ( )   PDF (505KB) ( )   Transformation of dielectric properties in uniaxial anisotropic perfectly matched layer(UPML) regions is explored and unified modeling of UPML is proposed.Two condensing optimized algorithms for auxiliary variables,six regions' intersected method and parameter-compressed method,are proposed.In three cycles all initialization of medium parameters and iterative coefficients in three directions are completed with unified modeling method.Though the six regions' intersected method saves a lot of memory,it is the slowest.The parameter-compressed method saves space,which is programmed easily and runs the fastest.

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Synthesis of Array Radiation and Scattering Patterns Including Mutual Coupling ZHANG Shuai, GONG Shuxi, GUAN Ying, GONG Qi 2011, 28(3): 420-426.  Abstract ( )   PDF (424KB) ( )   An analytical formula for radiation field of dipole arrays based on equivalent circuit theory was verified in previous works.We extend this concept to field scattered by dipole arrays.Based on analytical formulas,a method is proposed to synthesize desired radiation and scattering patterns of dipole arrays simultaneously by optimizing element positions with PSO.To verify accuracy and effectiveness of the method,a linear dipole array is designed to obtain low side lobe level radiation and scattering patterns.Good agreement between results with the proposed method and FEKO validates accuracy of the method.Maximum sidelobe level of radiation and scattering patterns at operating frequency are both reduced by optimization.Furthermore,maximum levels of MRCS patterns in-band at threat angles are also considerably reduced.

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Zero-reflectance at Surface of Periodic Grating Structures WANG Haitao, YE Hong 2011, 28(3): 427-432.  Abstract ( )   PDF (342KB) ( )   Periodic gratings with different shapes are designed to study spectral reflectivity in normal direction using finite-difference time-domain method.It shows that very low reflectivity in wavelengths can be found with proper grating structures and even zero-reflectance can be found.Influences of depth and slot width of triangle gratings on reflectance are investigated.Parameters for a triangle grating with very low reflectivity in wave bands of 2.75-3.23 μm and 3.84-4.88 μm are found.

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Particle Swarm Optimization for Automatic Optical Design in Engineering Optics QIN Hua, WAN Yunfang, ZHANG Weiyuan 2011, 28(3): 433-437.  Abstract ( )   PDF (292KB) ( )   We propose an application of Particle Swarm Optimization(PSO) in lens design.A mathematical model is constructed and a program code is developed.A fitness function is designed which combined radiuses of curvature,distances between lens surfaces and refractive indices in an optical system.Aberration correction is carried out with this function.An example using PSO is given.It shows that as a computer-aided optical design tools PSO is practical and powerful.It is no longer dependent on initial lens structure and creates arbitrarily search ranges of structure parameters,which is an important step towards automatic design with artificial intelligence.

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Simulation of Lower Hybrid Wave Power Deposition and Current Drive Control in EAST DUAN Wenxue, WU Bin 2011, 28(3): 438-444.  Abstract ( )   PDF (362KB) ( )   A modified code is used to study lower hybrid wave power deposition and current drive in EAST.Lower hybrid wave power spectrum,plasma density and temperature profiles are studied in a fixed non-circular magnetic equilibrium configuration of EAST.It shows that the lower hybrid wave deposition and current drive profile can be controlled with proper lower hybrid wave power spectrum,plasma density and temperature distribution.Near-axis and off-axis current drives can be controlled through adjusting plasma temperature distribution.

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Simulation of Mixing and Segregation of RDX and Al in a Revolving Drum HUANG Decai, LU Ming, ZHAO Shengxiang 2011, 28(3): 445-450.  Abstract ( )   PDF (554KB) ( )   Molecular dynamics is used to simulate binary granular of RDX and Al in a revolving drum.It shows that mixing quality is irrelative with filling method.In a drum without baffle plate on the wall,segregation of RDX and Al granule happens due to revolution of drum.With an added baffle plate on the drum wall,mixing effect is increased.Theoretical explanation is given for mixing and segregation.

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Electronic Structures of BaMgF4 Crystal with F Color Centres KNAG Lingling, LIU Tingyu, ZHANG Qiren, XU Lingzhi 2011, 28(3): 451-455.  Abstract ( )   PDF (306KB) ( )   Electronic structure of BaMgF4 crystal containing F color centers is studied within the framework of fully relativistic self-consistent Dirac-Slater theory,using a numerically discrete variational(DV-Xα) method.2p state of H atom is added into the program.It is concluded that energy levels of F color center are located in forbidden band of the crystal.Optical transition energy from ground state to excited state of the F color center is 5.12 eV,which corresponds to 242 nm absorption bands.They are well consisted with experiments.Absorption bands resulted from an F color center in BaMgF4 crystal are located in 236-274 nm.

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First Principles Study of Thermodynamic Properties of Cubic CeO2 HUANG Duohui, LUO Huafeng, YUAN Di, WANG Fanhou, JIANG Gang 2011, 28(3): 456-462.  Abstract ( )   PDF (430KB) ( )   Thermodynamic properties of cubic CeO2 with pressures up 30 GPa and temperatures up to 2 000 K are studied with first principles combined with a quasi-harmonic Debye model,including temperature dependence of equilibrium volumes,bulk modulus,heat capacity and entropy under ambient pressures.Heat capacity,entropy,Debye temperature and volume thermal expansion coefficient under different pressures are successfully obtained.Calculated heat capacity and entropy are in good agreement with experiments under ambient pressure.

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Interference of Three Bose-Einstein Condensates in One-dimensional Time-dependent Gross-Pitaevskii Equation CHE Lixin, LUO Xiangyi, SU Minghui 2011, 28(3): 463-468.  Abstract ( )   PDF (472KB) ( )   Symplectic method is applied to solve 1D time-dependent Gross-Pitaevskii(GP) equation numerically.Interference of three Bose-Einstein condensates(BECs) is investigated with or without a trapping potential.Elastic collisions of BECs occur as trapping potential exists.If trapping potential is zero at t=0,interference of three BECs is observed and oscillation of probability density is found.

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An Improved Algorithm for Choosing Delay Time in Phase Space Reconstruction ZHANG Jing, FAN Yangyu, LI Huimin, SUN Hengyi, JIA Meng 2011, 28(3): 469-474.  Abstract ( )   PDF (321KB) ( )   With embedding theorem proposed by Takens,we study methods for choosing proper delay time in phase space reconstruction of chaotic time series.A united method to incorporate advantages of average displacement and mutual information is put forward.In mutual information calculation we employ binary tree coding to divide and mark grids which makes it implemented easily.We determine layer numbers according to percentages of sparse grid.Numerical experiments of R ssler and Lorenz systems verifies accaracy of the method.