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25 March 2013, Volume 30 Issue 2 Previous Issue    Next Issue

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Multi-Block Lattice Boltzmann Method for Flows Around two Tandem Rotating Circular Cylinders TAO Shi, ZHOU Li, ZONG Zhi 2013, 30(2): 159-168.  Abstract ( )   PDF (3386KB) ( )   Flows past a pair of rotating circular cylinders in tandem arrangement at Re=100 are studied numerically.Multi-block lattice Boltzmann method(LBM) is used.Basic features of vortex shedding and forces acting on rotating circular cylinders are studied with comprehensive analysis of impact of cylindrical center spacing ratio S/D and rotational speed α.There exists a critical rotating speed at S/D=1.2,exceeding which the former cylinder produces a negative Magnus lift;As S/D=2,flow field emerges a second unstable mode similar to a single rotating cylinder;At relative large spacings(S/D=4、6),vortex sheds between cylinders.Wake flows of the later cylinder present a variety of forms of 2S、2S*、2P、P+S and so on.

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Reynolds-averaged Navier-Stokes Method with Laminar Kinetic Energy Turbulent Model GAN Wenbiao, ZHOU Zhou 2013, 30(2): 169-179.  Abstract ( )   PDF (2464KB) ( )   We set up simulation principles,and build simulation method and codes with laminar kinetic energy turbulent model,in which natural,bypass and separation translation are considered.Time derivatives of three-dimensional Navier-Stokes equations are preconditioned with Weiss-Smith preconditioning matrix.Effect of turbulent eddy viscosity is considered.Time split,spatial split and boundary conditions are specially treated to diagonal dominant matrix.Boundary layer and airfoil flow simulations are available.It is shown that the method is efficient and robust for basic aerodynamic flows.It provides reference to more complex flows.

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Configuration Design and Aerodynamic Research of New Type Tandem Buoyancy-Lifting Airships LI Feng, YE Zhengyin, GAO Chao 2013, 30(2): 180-186.  Abstract ( )   PDF (1816KB) ( )   Based on NACA airfoils,a new type of tandem buoyancy-lifting airships with both higher utility and economy efficiency was developed.With numerical simulations aerodynamic and configuration design for buoyancy-lifting airships was investigated and buoyancy-lifting characteristics were evaluated and analyzed synthetically.It shows that a tandem buoyancy-lifting airship has considerable volume efficiency.Its lift-drag ratio is increased 50% than single wing resulted from block of airflow by posterior flying-wing and speedup of airflow in overlay field.Its deadweight can be decreased and payload is increased as velocity is higher than 30 m·s-1.At the same time,chord wise size of tandem airship is comparatively small so that surface tension of skin material can be reduced availably.It provides a wider scope for skin flexible material selection of high altitude aircrafts.

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Free Surface Effect and Spike of a Cylinder Piercing Water Surface SUN Shili, SUN Yilong, HU Jingzhong, HU Jian 2013, 30(2): 187-193.  Abstract ( )   PDF (1770KB) ( )   To analyze force of fluid on a rigid object near free surface,a mathematical model with free surface effect is developed based on potential flow theory.It is calculated with boundary element method.Nonlinear kinematic and dynamic boundary conditions are taken into consideration.With control equation and boundary conditions,piercing cylinder through free surface and phenomena of spike are simulated.A comparison between numerical and experimental results shows that the method is appropriate.Pressure on moving objects,transform of free surface,resultant hydrodynamic force and velocity of flow field are analyzed in detail.It shows that the nonlinear method with free surface effect predicts precisely force on moving objects in vicinity of free surface.

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Convective Velocity Effect on Flame Shape and Combustion of Fuel Droplets HE Bo, FENG Songjiang, NIE Wansheng 2013, 30(2): 194-202.  Abstract ( )   PDF (2422KB) ( )   Considering gas phase unsteadiness and droplet internal recirculation,we developed an unsteady evaporation and combustion model for moving droplets.It adopts dynamic grid method tracking droplet interface location and conservation equations updating interface boundary conditions.Based on one step global chemical reaction,flame shape and combustion characteristics of n-heptance droplets at different convective velocity are simulated and analyzed.It shows that internal recirculation of moving droplet promotes low temperature area moving to the center of recirculation.Envelop flame translates into wake flame as convective velocity exceeding a critical value.Area of fuel rich and high temperature region and combustion rate at envelop flame are higher than those of wake flames remarkably.Droplet surface temperature and evaporation rate distribution at an envelop flame are different from those of wake flame obviously as well.

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A Combined Method of Rosseland Method and Two-flux Method for Combustion Within Porous Media LI Debo, SONG Zhengchang 2013, 30(2): 203-208.  Abstract ( )   PDF (1758KB) ( )   A combined method of Rosseland method and two-flux method is used for radiation heat transfer in premixed methane combustion within porous media.Numerical results show that the method is effective for computation of radiation heat transfer near boundary.

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Regularity of Gas Leakage from Scaled Underground Chemical Explosions WANG Tieliang, TIAN Zhou, WANG Zhanjiang, CAO Yuan, ZHANG Jianxin 2013, 30(2): 209-213.  Abstract ( )   PDF (1237KB) ( )   To forecast gas leakage of a planned experiment,harmful gas leaking time from a scaled underground explosion cavity and ratio of leaked harmful gas to entire harmful gas are studied with theoretical analysis and numerical simulation.The leakage mechanisms are:(1) gas leaks through uniform porous media,(2) gas leaks through non-uniform porous media,(3) gas leaks through fractures.It shows that leakage time is proportional to two thirds power of explosive amount in scaled underground explosions.Percentages of leaked gas are approximately same for scaled explosions in same media.Theoretical results about leakage time is basically in line with scaled experimental results.

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A Modified Levenberg-Marquardt Algorithm for Relevant Parameter Identification of Defect with Infrared Inspection LV Shigui, YANG Li, FAN Chunli, SUN Fengrui, WANG Weiqing 2013, 30(2): 214-220.  Abstract ( )   PDF (881KB) ( )   To overcome disadvantage of Levenberg-Marquardt(LM) algorithm,which can not keep geometric correlation of defect parameters,a modified method with fast convergence is presented.In a heat transfer model for a two-dimensional test piece with a subsurface rectangular defect,numerical experiments are conducted to verify effectiveness of the modified LM algorithm.Factors of initial guess and infrared temperature measurement error are considered.Conclusions are drown as follows: The modified LM algorithm keeps geometric correlation of defect parameters well and influence of initial guess is negligible;Identification accuracy of different defect parameters differs due to infrared temperature measurement errors.

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Simulation of Electronic Transport in Micro-channel Plate WANG Honggang, QIAN Yunsheng, WANG Yong, SHI Feng, CHANG Benkang, REN Ling 2013, 30(2): 221-228.  Abstract ( )   PDF (2304KB) ( )   To improve resolution of a low-light image intensifier,simulation of electronic transport in a micro-channel plate(MCP) is made.Field distribution is obtained by calculating electron optics with numerical method.Distribution of photoelectron on fluorescent screen is determined by tracing electron trajectory in MCP.Influence of MCP tilt angle,channel diameter,voltage on electronic transport and resolution of image intensifier are studied.It shows that MCP has good electronic transport characteristics,image intensifier has good modulation transfer function(MTF) and high resolution at a title angle of 14°,channel diameter of 5.0 μm,a voltage of 900 V.

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Meshless Models for Numerical Calculation of Scattering Coefficients of Periodic Structures WANG Haitao, ZENG Xiangyang 2013, 30(2): 229-236.  Abstract ( )   PDF (1363KB) ( )   Details for implementation of a Boundary Meshless Model (BMM) and a Meshless Plane Wave Decomposition Model (MPWD) calculating scattering coefficients of periodic structures with arbitrary shaped profiels are provided. BMM based on Mommertz's determination is applicable for finite samples. In contrast, numerical calculation is performed in a groove of one period in MPWD, which is applicable for samples with infinite surfaces. Random-incidence scattering coefficients of a sine-shaped sample and corresponding infinite sample are calculated using BMM and MPWD. Comparisons with measurements demonstrate that both models have good accuracy. Directional distributions of directional scattering coefficients are similar. At last, performances of the two models are discussed.

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Analysis of NMR Transversal Relaxation Based on ADI-FDTD Numerical Simulation GE Xinmin, FAN Yiren, ZENG Qingdong, WANG Mingfang, XU Yongjun 2013, 30(2): 237-243.  Abstract ( )   PDF (2276KB) ( )   To study influence of diffusion coefficient, relaxation rates, pore component ratio and pore width on NMR T2 distributions, a complex rock-pore system is simplified to an equivalent dual porosity medium in a mathematical physics model with Bloch's equation. ADI-FDTD and SIRT methods are used in numerical simulations of NMR transversal response and decomposition of NMR T2 spectrum, respectively. It shows that transversal magnetization vector decay rate is proportional to diffusion coefficient and micro porosity, inversely proportional to pore width and nearly irrelevant to surface relaxation rate. NMR T2 spectrum hardly reflects pore components and structure as diffusion coefficient is small and pore width is large. Special attentions should be paid to influence of diffusion coefficient and pore-size as evaluating pore structure by NMR.

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Monte Carlo Simulation of Nematic Droplets with Modified Gruhn-Hess Pair Potential ZHANG Yanjun, WANG Chao, YE Wenjiang, ZHANG Zhidong 2013, 30(2): 244-250.  Abstract ( )   PDF (370KB) ( )   Nematic droplets are studied with Monte Carlo simulations with a modified Gruhn-Hess pair potential. The potential is spatially anisotropic and potential parameters are related to elastic constants K11 ,K22 ,K33 and surface-like elastic constant K13. It is assumed that nematic droplet surface is a free surface. Second order parameters and introrse intensity, which describes quantitatively intrinsic anchoring induced by surface at low temperatures, are calculated with a modified Gruhn-Hess pair potential and are compared with those in Gruhn-Hess model I. It is shown that the modified model with K13 induces intrinsic anchoring near droplet surface, orientation and intrinsic anchoring strength depend strongly on K13, and introrse intensity is related to K33/K11. Order degree of nematic droplet is lower from inner shell to outer shell due to incomplete anisotropic nematic-nematic interactions.

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Self-assembly of Asymmetric Coil-Rod-Coil ABA Triblock Copolymers:Self-consistent Field Study WANG Biao, LI Yunfei, HAN Xianggang 2013, 30(2): 251-255.  Abstract ( )   PDF (717KB) ( )   Self-assembly of asymmetric coil-rod-coil three block copolymers is simulated with self-consistent field theory in three dimensions. As volume proportions of coil and rod block equal each other, with change of volume fractions of aside coil, lamellar, gyroid, strip and cylindrical structures are observed. Interacion parameter at which phase separation occurs increases with volume fractions of aside coil. As volume fraction of aside coil equals 0.05, phase behaves especially rich. With increasing interacion parameter self-assembly structure change from lamellar into gyroid and then lamellar, which is different from coil-rod diblock copolymers. It is found that appearance of lamellar, gyroid, strip and cylindrical structures differs with corresponding coil-rod-coil symmetric tfiblock copolymers.

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First-principles Study of Structure, Elastic and Thermodynamic Properties of ZrV2 LIU Xiankun, ZHENG Zhou, LAN Xiaohua, LIU Cong 2013, 30(2): 256-264.  Abstract ( )   PDF (936KB) ( )   Structure and elastic property of ZrV2 under high pressure are investigated with first-principles calculations based on plane-wave pseudo-potetial in the framework of density functional theory within generalized gradient approximation (GGA). With a quasi-harmonic Debye model, in which phonon effects are considered, we calculated thermodynamic properties of ZrV2 in a pressure range from 0 to 20 GPa and temperature range from 0 to 1200 K. Pressure dependence of elastic constants, bulk modulus and heat capacity, and thermal expansion with pressure and temperature are presented. It shows that calculated lattice parameters of ZrV2 are in good agreement with existing experimental data and other theoretical results. Elastic constants, Debye temperature and bulk modulus increases with increasing pressure. Relative volume, heat capacity decreases with increasing pressure. Temperature effect is weaker than pressure effect in thermal expansion of ZrV2 under high pressures.

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Effect of Hydrostatic Pressure on Optical Properties of TlBr and TlCl Amrane N, Benkraouda M 2013, 30(2): 265-270.  Abstract ( )   PDF (805KB) ( )   We present first principles calculations of optical properties of binary semiconductor compounds TlBr and TlCl.Dependences of dielectric function,reflectivity and refractive index on hydrostatic pressure are calculated using self-consistent scalar relativistic full potential linear augmented plane wave method(FP-LAPW) within a generalized gradient approximation(GGA).They are compared with previous calculations and experimental measurements.Good agreements are found.

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Thermodynamic Properties of Cubic KNO2 under Atmospheric Pressures:Density Functional Study PENG Qiang, YANG Xiaoxi, DING Jing, WEI Xiaolan, LU Jianfeng, YANG Jianping 2013, 30(2): 271-276.  Abstract ( )   PDF (780KB) ( )   To understand performance of molten salt heat transfer and thermal storage in solar thermal power system, thermodynamic properties of cubic KNO2 under atmospheric pressure and temperatures between 300 and 725 K are studied with density functional theory combined with a quasi-harmonic Debye model. Temperature dependence of isobaric heat capacity, isochoric heat capacity, entropy, Debye temperature, volume thermal expansion coefficient, equilibrium volumes and bulk modulus under ambient pressure are calculated. It shows that calculated isobaric heat capacities are in good agreement with experiments under ambient pressures. Both entropy vary greatly. The average volume thermal expansion coefficient-is 1.837 8×10-5K-1 and Debye temperature is 667.13K at ambient temperatures, respectively.

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Electronic Structures of Unsaturated and H Saturated GaN Nanowires LI Enling, XI Meng, CUI Zhen, CHENG Xuhui, XU Rui, MA Deming, LIU Mancang, WANG Xuewen 2013, 30(2): 277-284.  Abstract ( )   PDF (2295KB) ( )   Electronic structures of unsaturated and H saturated GaN nanowires with diameters of 9.5Å, 15.9Å and 22.5Å are studied with generalized gradient approximation (GGA) of density functional theory (DFT). Results show that unsaturated and H saturated GaN nanowires have direct band gaps. Band gaps of unsaturated GaN nanowires decrease with the increase of nanowire diameter, but not significantly. Band gaps of H saturated GaN nanowires decrease with the increase of nanowire diameter as well. They are more apparent than unsaturated ones. 2p electrons of N atoms in surface of unsaturated GaN nanowires locate at top of valence band, and 4p electrons of Ga atoms in surface locate at bottom of conduction band. These two kinds of electrons are local which decide the band gap. Surface effect of surface atoms can be eliminated by saturating with hydrogen atoms.

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Density Functional Study of Mg-AI-N Ternary Clusters LI Jing, LIU Xiaoyong, LIAO Liangqing, SHENG Yong 2013, 30(2): 285-295.  Abstract ( )   PDF (1991KB) ( )   Geometries of MgxAlyN (x,y=1-5) clusters are studied by using hybrid density functional theory (B3LYP) with 6-311+G* basis sets. For lowest-energy structures of MgxAlyN clusters, stabilities and electronic properties are investigated. It shows that planar structures are dominant structures of MgxAlyN (x+y≤4) clusters. The lowest-lying MgxAlyN clusters mostly derived from ground-state structures of AlnN or Mgx-1Aly+1N clusters. MgxAlyN clusters are stable with respect to fragmentation into atoms or smaller clusters. Compared with neighboring clusters, MgAl3N and Mg3Al3N clusters own higher stability. For all MgxAlyN clusters studied, we found co-existence of covalent, ionic, and metallic bonding characteristics. Furthermore, ionization potential and electron affinity exhibit weak oscillations as increasing cluster size. Ro general pattern is observed.

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Calculation of Accurate and Concise Analytic Atomic Configuration Interaction Wave Functions MA Ying, XIONG Zhuang, WANG Zhenxin 2013, 30(2): 296-302.  Abstract ( )   PDF (350KB) ( )   We developed a code for ab-initio variational configuration interaction calculation of electronic structure of atoms via generalised Laguerre type orbitals. By computing absolute minimum of energy with orbital effective charges as variational parameters optimal wave functions are obtained. Algorithm and program structure are presented in details. A convergence study of our CI method with NMCSCF is given for He 1s21S state. It shows that convergence of our CI method is faster than that of NMCSCF method. As an example, absolute minimum of energy and optimal wave functions of Ti in 5G states are calculated.

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“Detail History” Monte Carlo Method for Ion Simulation Wang Guanbo, Yang Xin, Liu Hangang, Wang Kan 2013, 30(2): 303-308.  Abstract ( )   PDF (289KB) ( )   Principles of ion interaction with target atoms including nucleus and electrons are introduced. We study "detail history" Monte Carlo method. An ion Monte Carlo simulation code ITR (ions transport and reaction) was developed. It shows that our code perform good results compared with TRIM and Corteo. It is faster than TRIM.

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Cause Analysis of Growing and Non-growing Scale-free Networks QIAO Jian, FAN Ying, LI Guoying 2013, 30(2): 309-316.  Abstract ( )   PDF (2290KB) ( )   Causes of two classes of scale-free networks are analyzed. A scale-free network evolution model is proposed and a series of numerical experiments are carried out. Theoretical analysis and numerical experiments show that if network density is sparse and stable enough, a persistently stable scale-free network can be produced by degree-based preferential attachment. Growth of network size as well as addition and deletion of vertices and edges are objective realities. They have the function of controlling network density as well. A sufficiently sparse density and degree-based preferential attachment are common necessities of scale-free networks. This deduction can be used to explain reasonably the cause of growing and non-growing scale-free networks. The results are helpful in understanding diversified real scale-free networks and design of corresponding models.