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25 March 2016, Volume 33 Issue 2 Previous Issue    Next Issue

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Geometric Free Path of Supersonic Radiative Diffusion Wave in Concentric Shell Structrues ZHAO Yingkui, WEN Wu, ZHU Ruidong, OUYANG Biyao, WANG Min 2016, 33(2): 127-135.  Abstract ( )   HTML ( )   PDF (726KB) ( )   With local thermodynamic equilibrium approximation,radial position-dependent energy flux for diffusive supersonic wave in low density filled cylinder or sphere shell structures with high density walls are given. We obtain arched-type distribution of geometric factor versus radius in cylinder and sphere shell structure. Mean geometric factor is obtained from cross-section average of total radiative energy flux. Effect of spherical shell structure on radiation process is much greaterr than that of cylinder structure. Geometrical free path must be considered in simulation of radiative diffusivity or thermal conductivity for sphere shell structures models. A fitted formula of geometric factor according to numerical solutions is given.

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Monte Carlo Simulation for Inverse Compton Scattering LONG Guangbo, ZHENG Yonggang, OU Jianwen, WANG Xinghua, HUANG Xia, WANG Yanfang 2016, 33(2): 136-146.  Abstract ( )   HTML ( )   PDF (1108KB) ( )   Monte Carlo simulation for inverse Compton scattering in homogeneous isotropic media is studied. We analyze sample efficiency of rejection method that describes electronic speed and photon scattering direction. We also improve method of inverse functions for electron velocity distribution and composition-rejection methods for photon scattering energy distribution. We define application regime of these drawing methods by comparing their efficiency.

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Lattice Boltzmann Modeling of Non-Newtonian Multiphase Fluid Displacement XIE Chiyu, ZHANG Jianying, WANG Moran 2016, 33(2): 147-155.  Abstract ( )   HTML ( )   PDF (1551KB) ( )   Non-Newtonian fluid model is introduced into multiphase LBM to investigate non-Newtonian fluid displacement in porous media. To begin with,process of a Newtonian fluid displaced by pseudo-plastic fluid and Newtonian fluid in a simple pore with a small obstacle is studied. It shows that fluid displaced by pseudo-plastic fluid is faster than that by Newtonian fluid. Besides,interface tension effects on displacement process is investigated in detail. It indicates that interface tension plays a resistant role during displacement process. Lower interface tension enhances displacement. By using quartet structure generation set (QSGS) algorithm,we perform a series of modeling of displacement in porous media systems. Impacts of interface tension,wettability and pressure difference on final production are discussed.

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Lattice Boltzmann Study of Nonlinear Characteristics of Double Diffusive Mixed Convection in an Enclosure LI Beibei, WANG Tingting, CHEN Jian, XU Hongtao, YANG Mo 2016, 33(2): 156-162.  Abstract ( )   HTML ( )   PDF (1311KB) ( )   Lattice Boltzmann method is adopted to numerically analyze nonlinear characteristics of double diffusive mixed convection in an enclosure. A heated cylinder is located at center of the enclosure. Fluid flows from an inlet at lower-left wall of enclosure and an outlet is at upper-right,upper-middle and upper-left wall respectively. Simulation results indicate that there are steady stationary solution,periodic and aperiodic oscillatory solutions in double diffusive mixed convection at different parameters. Phase path of velocity of monitoring point finally reaches a point,a closed loop and irregular curves,respectively.

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Mechanism of Transition Delay by Porous Surface in Hypersonic Boundary Layers ZHU Dehua, LIU Zhiyong, YUAN Xiangjiang 2016, 33(2): 163-169.  Abstract ( )   HTML ( )   PDF (764KB) ( )   Mechanism of transition delay by porous surface in hypersonic boundary layers is investigated. Linear stability theory (LST) is adopted to analyze characteristics of instability and comparisons with direct numerical simulation (DNS) are made. Under conditions Ma=6.0,Re=2.0×104 (length scaled by displacement thickness of boundary layer),typical flow characteristics are obtained for planar boundary layers with and without distributed pores. Disturbing growth rate of smooth and porous boundary layers are computed by LST. N-factor,which is regarded as a symbol of accumulated growing of disturbance,is calculated. It shows that pores prohibit growth of Mack's mode and therefore delay transition of hypersonic boundary layer. Sequence-distributed pores stabilize boundary-layer flow more effectively than interlace-distributed pores.

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CFD Analysis on Pilot's Injury by Windblast at High Speed ZHANG Peng, TIAN Jialin, HAN Lujia, LIU jie 2016, 33(2): 170-176.  Abstract ( )   HTML ( )   PDF (948KB) ( )   To investigate injury of windblast at high speed,flow around a seat occupant is simulated in a scale adaptive simulation turbulence model. Numerical simulations agree well with wind tunnel experiments at Mach number 0.6 and angles of attack from -90° to 90°. Flow around seat occupant without protection is simulated. Injury of pilot during high speed ejection is investigated. It shows that high pressure zones load on pilot are face,thorax,abdomen,inside of upper arm and windward side of calves. As pitch angle increases pressure distribution on each part can improve.

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A Birth-Death Process Model for Number of Drops with Collision and Coalescence XUE Shesheng, XU Ming 2016, 33(2): 177-182.  Abstract ( )   HTML ( )   PDF (331KB) ( )   Collision and coalescence among drops is an important phenomena in gas/drop two-phase flows. To study change of number of drops caused by collision and coalescence,a special flow field is considered in which liquid phase consists of two classes of drops with big or small sizes. Probability for collision and coalescence between a big drop and a small drop is derived. Considering three factors of immigration,emigration and collision of drops,a model of birth-death process is proposed for number of drops located in a fixed observation region,and relevant unconditional probability model equation is deduced. Finally,stationary distribution is obtained. As an illustration,mass creament of a falling rain drop is calculated.

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A Parallel SPH Method with Background Grid of Adaptive Mesh Refinement GONG Xiangfei, YANG Jiming, ZHANG Shudao 2016, 33(2): 183-189.  Abstract ( )   HTML ( )   PDF (959KB) ( )   We present a distributed parallel SPH programming algorithm using adaptive mesh refinement background grids,in which size of a grid is decided based on maximal smoothed length of local particles. All neighboring particles of a given particle can be found in the grid the particle belongs to and in grids of same size adjoining to this grid. Searching bound is confined and as a result computational efficiency is improved. The method is validated in non-uniform smoothed length SPH simulation.

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Calculation of Water Breakthrough Time in Well Patterns of Ultra-low Permeability Reservoir HE Congge, FAN Zifei, XU Anzhu, FANG Sidong, LI Bokai 2016, 33(2): 190-196.  Abstract ( )   HTML ( )   PDF (619KB) ( )   As ultra-low permeability reservoir is developed by water flooding,it always presents characteristics of non-Darcy flow and permeability anisotropy. We derived water breakthrough time formula of five-spot well pattern,inverted nine-spot well pattern and rhombic nine-spot well pattern with basic non-Darcy flow formula and streamline integral method. Breakthrough time of one actual well pattern in Ordos Basin was calculated. Calculation results accorded with production data well. Effects of threshold pressure gradient, permeability anisotropy and viscosity difference between oil and water were analyzed. It shows that the greater the viscosity ratio of oil and water,the earlier the water breakthrough time; Corner well of rhombic nine-spot well pattern can realize uniform displacement both in x direction and y direction as ratio of well spacing in x direction and y direction equals to permeability anisotropy degree; The grenter the threshold pressure gradient,the latter the water breakthrough time. Effect of threshold pressure gradient became more apparent as well spacing is larger.

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Transient Analysis and Computation of Transmission Line Based on WLP-FDTD Method YU Pei, LI Xiaochun, WANG Ning, MAO Junfa 2016, 33(2): 197-204.  Abstract ( )   HTML ( )   PDF (565KB) ( )   Weighted Laguerre polynomials-finite difference time domain (WLP-FDTD) method is employed to analyze transient response of transmission line in high-speed interconnect circuit system. Based on telegraph equation in equivalent circuit networks model,current and voltage are computed with weighted Laguerre polynomials. According to orthogonality,stability condition is eliminated. Different from finite difference time domain method,WLP-FDTD method is unconditional stable,which separates time and space variables. It is fast in computing large number of dissection networks for a transmission line. It shows that WLP-FDTD method is more efficient than traditional FDTD in analysis of transmission line. At last,a program with GUI is developed.

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Seismic Wave Pre-Stack Reverse-Time Migration Imaging Condition Based on One-Way Wave Field Separation and Angle Domain Attenuation CHEN Keyang 2016, 33(2): 205-211.  Abstract ( )   HTML ( )   PDF (580KB) ( )   To improve seismic wave reverse-time migration (RTM) quality of complex structures,a new RTM imaging condition is shown. Take 2D model as example,one-way wave field and formation reflection angle with Poynting vector are obtained. Correlation calculation between up-way and down-way wave field,and between left-way and right-way wave field of shot and receiver are made, which removes migration noise components. Further,it introduces weight of cosine function of reflection angle into cross-correlation RTM imaging condition to suppress noise. Model study shows that main cause of migration noise is cross-correlation image of different shot and receiver point propagating direction wave field. Cross-correlation image of same shot and receiver point propagating direction wave field can suppress migration noise effectively and maintain imaging ability on sharp angle layer and horizontal surface as well. Imaging results can be further improved with weight of cosine function. Practical seismic data verify the method. In summary,the imaging condition provides an important method guide for improving imaging quality in complex structure area.

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Solitary Waves with Double Kinks of mBBM Equation and Their Dynamical Stabilities WANG Linxue, ZONG Jin, WANG Xueling, SHI Yuren 2016, 33(2): 212-220.  Abstract ( )   HTML ( )   PDF (548KB) ( )   We obtained a class of solitary wave solutions of modified Benjamin-Bona-Mahony (mBBM) equation with kink-antikink structure by using hybolic-function expansion method. Solitary wave solution reduces to a kink-like solution or bell-like solution under different limitations. We analyzed structures of solitary wave with double kinks. Dynamical stability is investigated numerically with a finite difference scheme. The scheme is implicit and it is absolutely stable in linearization sense. It indicates that single soliton with double kinks is stable under different disturbances. Meanwhile,collision of two solitary waves is numerically simulated. It was found that collision between two solitary waves can be either elastic or inelastic.

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First-Principles Study of Electronic and Optical Properties of BxGa1-xAs Alloy YAN Yingce, WANG Yanlong, MA Huifang 2016, 33(2): 221-228.  Abstract ( )   HTML ( )   PDF (473KB) ( )   First-principles calculations based on density functional theory are performed for zinc-blende BxGa1-xAs alloy with a special quasirandom structure (SQS) approach in a 64-atom supercell. Structural,electronic and optical properties of BxGa1-xAs alloy are comprehensively investigated under optimized geometry structures. It was found that calculated lattice constant slightly deviated from Vegard's law and significant bond length relaxation is shown. Calculated bowing parameters of energy gap are small (2.57 eV-5.01 eV) and are weakly composition-dependent. Finally,effects of boron composition on optical parameters including dielectric function, reflectivity,refractive index,absorption coefficient and energy loss function are analyzed in detail.

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Directional and Topological Orders in a Two-Dimensional Compass-XY Model on a Square Lattice LI Yushan, WAN Wenzhi 2016, 33(2): 229-233.  Abstract ( )   HTML ( )   PDF (577KB) ( )   Two-dimensional Compass-XY model on a square lattice is investigated by means of Monte Carlo method. Effects of decreasing frustration of exchange interactions on directional and topological orders are studied by adjusting crossover parameter α. It is demonstrated that crossover between directional and topological orders is a gradual process,which means that there is no distinct barrier. Two kinds of ordering are partly overlapped within a certain range,making it difficult to tell them apart. Decrease of frustration facilitates topological order while suppressing directional order. Directional order may be destroyed as frustration is weak enough.

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Time Characteristics of Group Interaction Behavior in Online Social Network LI Xujun, LIU Yezheng, JIANG Yuanchun 2016, 33(2): 234-252.  Abstract ( )   HTML ( )   PDF (3271KB) ( )   For interaction behavior of users in online social networks,we build a biased diffusion model to explain time interval distribution characteristics of group posting and event by relating task interval time τ and task execution time θ. We demonstrate that, for τ≥θ,time intervals follow power law distribution; and for τ>>θ,time intervals follow power law distribution with exponential effect. Experimental results validate the model.