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25 November 2014, Volume 31 Issue 6 Previous Issue    Next Issue

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PML Absorbing Boundary Conditions for Nonlinear Euler Equations ZHENG Chunxiong, Tareq Amro 2014, 31(6): 631-647.  Abstract ( )   PDF (3845KB) ( )   Perfectly matched layer (PML) absorbing boundary conditions (ABC) are presented for nonlinear Euler equations in unbounded domains. The basic idea consists of two steps. First,PML technique is applied to linearized Euler equations in either a uniform mean flow or a parallel mean flow. Nonlinear PML equations are then derived by replacing flux functions in linearized Euler equations with nonlinear counterparts. Since a stiff source term gets involved in PML equations,an implicit-explicit Runge-Kutta scheme is proposed to integrate discrete ODE system. Numerical experiments are performed. They demonstrate advantage of proposed PML ABC over traditional characteristic boundary condition.

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A Shock-pinned Random Projection Method for Multi-directional Stiff Detonation Capturing WANG Jianhang, CHEN Fang, LIU Hong, WANG Lan, ZHENG Zhonghua 2014, 31(6): 648-658.  Abstract ( )   PDF (6285KB) ( )   A shock-pinned random projection method( SRPM) is proposed. To overcome difficulty of multidirectional propagation,local random projection is applied by introducing a shock indicator along with proper rules for choosing local projection zones around shocks in each reaction step. Numerical experiments are presented. It shows that SRPM is appropriate for detonation waves with multi-directional propagation,which is high-efficient in solving stiff reactive equations and extensible to 3D situations.

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Numerical Study of Shock Interactions with Rectangular Density Interface in Magnetohydrodynamics LI Yuan, LUO Xisheng 2014, 31(6): 659-667.  Abstract ( )   PDF (2906KB) ( )   A magnetohydrodynamic simulation method is developed for shock interacting with rectangular density interface in a magnetic field. The method employs 3rd WENO scheme and mixed GLM method. With circular polarized Alfvén wave propagation test and rotated shock tube problem,the method is validated. Under conditions that Mach number of shock is 10 and ratio of density of cloud to ambient gas is 10,evolutions of shocked interface in different initial orientations and strengths of magnetic field are compared.It shows that magnetic field decreases vorticity formed on surface and reduces growth of hydrodynamic instabilities; Field influences acceleration and mixing rate of cloud; And field is greatly amplified in some regions behind shock when cloud is presented. It is also found that,due to sharp corner,evolution of rectangular interface is different from circular one.

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Impact of Trajectory Deviations on Aerodynamic Characteristics of Mars Science Laboratory LV Junming, MIAO Wenbo, CHENG Xiaoli, WANG Qiang 2014, 31(6): 668-674.  Abstract ( )   PDF (4382KB) ( )   Three-dimensional Navier-Stokes equations in real gas models are solved with a parallel code to analyze aerodynamic characteristics of Mars Science Laboratory in hypersonic entry in Martian atmosphere. Good agreement between numerical results and flight data of Viking validates physical-chemical models and numerical methods. It shows that impacted by real gas effect,shock layer thickness is reduced; drag coefficient rises,lift coefficient is almost unchanged. Difference of trim angle between real gas and perfect gas is about 2.2°; As keeping altitude,greater Mach number results in greater drag and pitching moment coefficient. Difference of trim angle varies from 1.6° to 2.6°. Increasing Mach number enhances real gas effect. As keeping Mach number,increasing altitude weakens chemical reactions behind the shock,but it has weak influence on aerodynamic coefficient.

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Temperature Conditions of Bénard Convection QI Jingang, GAO Yong, ZHAO Zuofu, WANG Jiayi, LI Yang, WU Di, WANG Jianzhong 2014, 31(6): 675-680.  Abstract ( )   PDF (870KB) ( )   Disturbance equations of velocity and temperature fields are built based on Boussinesq approximation,in which second order and higher-order disturbance of Bénard convection are ignored. Transcendental equations controlling Bénard convection are obtained with non-dimensional treatment of variables. Specific parameters of Bénard convection are obtained,which provide reference and guidance for Bénard convection experiments.

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Numerical Simulation of Coalbed Methane Displacement with Gas Injection WU Jintao, HOU Jian, LU Xuejiao, YU Bo 2014, 31(6): 681-689.  Abstract ( )   PDF (4626KB) ( )   A double medium mathematical model for coalbed methane displacement with gas injection is established. Multi-physics coupling process containing Darcy flow,adsorption/desorption and diffusion of multiple component gas and variation of porosity and permeability is involved. The model is solved numerically with finite difference method and validity of the model is verified. In example simulation calculations,improved recovery,evolution of produced gas composition and variation of coal seam properties under injection of CO2、N2and 70% N2+ 30% CO2 are contrastively analyzed. It indicates that injections of CO2、N2and their mixed gas are able to improve coalbed methane recovery significantly by a degree over 28 %. N2 breaks through rapidly after injected,while CO2 occurs in production well later. Shrinkage /swell effect plays a dominant role in variation of porosity and permeability after gas injection.Adsorption of CO2 reduces porosity and permeability,while adsorption of N2 leads their increase.

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Prediction of Steam Chamber Development and Production Performance for SAGD in Thin Heavy Oil Reservoirs WEI Shaolei, CHENG Linsong, HUANG Wenjun, ZHANG Huideng 2014, 31(6): 690-698.  Abstract ( )   PDF (3033KB) ( )   Based on analyses of SAGD field production data and numerical simulations,SAGD production process in thin heavy oil reservoirs was divided into periods: steam chamber horizontal expansion period and steam chamber downwards migration period. A model was built,which includes mass conservation equation,energy conservation equation and heat loss equation. A comprehensive mathematical expression was obtained to describe steam chamber development process. The expression is a typical Volterra integral function of the second kind,which could be solved by Laplace transformation. Comparisons were made between the model and CMG Stars'. A small relative error,less than 5% for the whole SAGD production process,was found. The model provides an accurate and quick method for determination of limited reservoir properties and proper production parameters for SAGD production.

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Effect of Solar Radiation on Evaporation of Still Water Surface SUN Fengxian, LIU Changyu, XIA Xinlin, AI Qing 2014, 31(6): 699-705.  Abstract ( )   PDF (1943KB) ( )   An evaporation model at steady state was bulit to analyse effect of solar radiation on evaporation of still water surface at low airflow velocity. It considers convective heat and mass transfer from water surface to airflow,interior heat transfer and solar radiation absorbing spectrum of water. Finite volume method combined with Monte Carlo method and spectral band model are used to simulate energy and mass transfer among water interior,surface and airflow. Effect of solar irradiance on evaporation rate of water surface was analysed at different airflow velocity,humidity,temperature,forward and inverse temperature difference. It shows that solar irradiance effect on evaporation of still water surface is great at low airflow velocity.

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Effect of Particles-piled on Energy Attenuation at High Temperature and High Pressure WANG Hongliang, TIAN Zhou, GUO Yonghui 2014, 31(6): 706-712.  Abstract ( )   PDF (2228KB) ( )   Two-dimensional axi-symmetric gas-solid two-fluid model was established. Under three conditions of source: E0/10,E0/100,E0/1 000 (initial energy per mass of gas),diminishing of gas energy and gas pressure caused by packing particles was studied. It shows that: With higher initial energy per mass of source kinetic and internal energy of gas is diminished by packing particles more quickly,gas fluid is close to stillness more quickly,gas pressure is decreased more quickly.

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Plasmon Resonances in Sodium Clusters with Triangle Structure YIN Haifeng, ZENG Chunhua 2014, 31(6): 713-718.  Abstract ( )   PDF (1629KB) ( )   Plasmon excitation in small sodium clusters with triangle structure is studied with time-dependent density functional theory. For relatively larger sodium clusters,along triangle bottom edge and perpendicular bisector of triangle bottom edge,linear shapes of absorption spectra and resonance energies of main absorption peaks are same. However,along these directions,resonance modes of main absorption peaks are different. For the main plasmon mode,field enhancement extrema are located in region of endpoints of the triangle.

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Electronic and Lattice Dynamic Properties of Ternary Intermetallic SrAlSi Under High Pressure LIU Zhichao, CUI Xuehan, GU Guangrui, WU Baojia 2014, 31(6): 719-726.  Abstract ( )   PDF (2194KB) ( )   Electronic and lattice dynamic properties of ternary intermetallic SrAlSi are studied with first-principles calculations based on density functional theory under high pressures. SrAlSi has a similar hexagon-honeycombed structure to MgB2,where Sr atoms substitute Mg atoms,Al and Si atoms randomly occupy the positions of B atoms. It is found that under high pressure electronic topological transition( ETT) occur in the band of SrAlSi near Fermi surface. Lattice dynamics of SrAlSi are studied by phonon dispersion spectra at different pressures. The calculation shows that optical branches soften along A-L-H line and phonon modes harden with increase of pressure. It is indicated that structure of intermetallic compound SrAlSi is unstable under high pressures.

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Structural,Photoelectric and Magnetic Properties of Mn(SiO2)3(M=Fe,Co,Ni;n=1-3) Clusters ZHI Lili, LI Yanqing, YANG Lianhong, ZHAO Gaofeng 2014, 31(6): 727-734.  Abstract ( )   PDF (4558KB) ( )   Equilibrium geometries,electronic and magnetic properties of Mn(SiO2)3(M= Fe,Co,Ni;n=1-3) clusters are systematically studied employing density functional theory with a generalized gradient approximation. It shows that Fe and Co atoms are easier to congregate on (SiO2)3 cluster than Ni atoms. It is found that stabler silica is an excellent matrix materials to carry islands of transition-metals. Energy gaps of Mn(SiO2)3(M=Fe,Co,Ni;n=1-3) clusters lie in near infrared radiation region. In analysis of magnetism,it is found that their magnetic moments are mainly located on transition-metal atoms. Fe2(SiO2)3 and Co3(SiO2)3 have greater magnetic moments,owing to coupling between d orbits of transition-metal atoms. Energy gap and magnetic property affirm a considerable foreground of magnetic-mulriple silica used for photodynamic target therapy in medical stage.

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Particle Aggregation in Parallel Force Field CHEN Le, YU Xiaoyan, ZHENG Rongsen 2014, 31(6): 735-741.  Abstract ( )   PDF (2823KB) ( )   In diffusion limited aggregation( DLA) model,particle aggregation in parallel field is investigated. It shows that symmetry of particle aggregation is destroyed and particle density is increased. Aggregation pattern transforms fractal into compaction and growth location of aggregation transforms into saturated growth region. As intensity of parallel force field is stronger,aggregation grows faster and particle density is higher.

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Linkage Fluctuation in Double Variables of Time Series Based on Complex Networks AN haigang 2014, 31(6): 742-750.  Abstract ( )   PDF (1504KB) ( )   To study linkage fluctuation of double variables of time series,we took London Gold and Au9999. Model of linkage fluctuation is consisted of characters {P,N,M},using coarse graining process. Nodes of complex network are 5-symbol strings. Linkage fluctuation complex network is composed of all models and link edges between them. It indicates that models have power-law distribution,clustering and periodicity. Transmission and evolution are finished mainly by few models. It provides an analyzing method for many kinds of double variables of time series and ideas for general law of multi-variables of time series,as well.

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Immunity of Rumor on Scale-free Network with Tunable Clustering HE Yuyu, ZOU Yanli, XU Xuanfeng, ZHENG Jing 2014, 31(6): 751-766.  Abstract ( )   PDF (1629KB) ( )   We present a cluster immunization strategy and study its immune effect on scale-free network with tunable clustering in a modified classic rumor propagation model. Study shows that effect of cluster immunization becomes better with increasing of network clustering coefficient. Several immunization strategies including target immunization, betweenness immunization, closeness immunization and cluster immunization are compared. It shows that betweenness immunization is always the best regardless of network clustering. As a network clustering coefficient is relatively great,effect of cluster immunization is better than that of closeness immunization and close to target immunization. With further increasing network clustering coefficient,cluster immunization exceeds target immunization and approaches to betweenness immunization.