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25 January 2015, Volume 32 Issue 1 Previous Issue    Next Issue

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A Flux Splitting Scheme Based on AUSM LI Xindong, HU Zongmin, ZHANG Deliang, JIANG Zonglin 2015, 32(1): 1-12.  Abstract ( )   PDF (5836KB) ( )   According to advection upstream splitting method,a flux splitting method called K-CUSP is proposed.The greatest difference between K-CUSP and two traditional CUSP schemes,namely H-CUSP and E-CUSP,is splitting of total energy:All kinematic quantities and thermodynamic quantities should be separately split into convective term and pressure term by K-CUSP scheme.Numerical tests indicate that:① K-CUSP scheme inherits the simplicity and robustness of FVS scheme.It is less prone to pressure overshoot after shock and no oscillations in expansion area,which is better than AUSM and WPS schemes.② K-CUSP scheme also inherits resolution of FDS scheme.Shock resolution is almost the same with H-CUSP and E-CUSP schemes.Contact discontinuity resolution is better than FVS schemes,a little worse than Roe,AUSM and WPS schemes.However,velocity of contact discontinuity in AUSM and WPS schemes exist large oscillation,while our scheme does not.

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Least-squares Finite Element Method for Unsteady Stress Formulation of Navier-Stokes Equations SUN Chenyang, LI Qiliang, YANG Zhigang 2015, 32(1): 13-19.  Abstract ( )   PDF (2754KB) ( )   To solve unsteady laminar flow problems,a method of velocity-stress-pressure formulation instead of velocity-vorticitypressure formulation is developed.With Newton's linearized method to linearize convective terms and preconditioned conjugate gradient method to solve equations,unsteady stress formulation of Navier-Stokes equations is solved.Comparison between numerical and experimental results of cavity laminar flow shows that result of stress formulation fits experiment better and has higher accuracy than vorticity formulation.The stress formulation can deal with subgrid stress with least squares finite element method.Comparison with experimental results of cavity turbulent flow reveals feasibility of the method.It lays a firm foundation for large eddy simulation computation.

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GPU Accelerated Lattice Boltzmann Simulation of Flow in Porous Media ZHU Lianhua, GUO Zhaoli 2015, 32(1): 20-26.  Abstract ( )   PDF (1861KB) ( )   A sparse lattice representation lattice Boltzmann method algorithm is implemented on Graphics Processing Units (GPU) to accelerate pore scale flow simuation.Prefomance testing shows that sparse lattice representation approach grately reduces memory requirement and maintains performance under low porosity compared with basic algorithm.Overall speedup reaches two orders of magnitude compared with serial code.Various factors including collision model,float number precision,and GPU that affect computing speed of the algorithm are invesgated independently.It indicates that MRT model runs as fast as LBGK model on new generation of GPU cards.While on old GPU cards,MRT model's computing speed matchs LBGK only when using single precision float.

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Plasma Prediction of Reentry Vehicle and Gas Components MIAO Wenbo, HUANG Fei, CHENG Xiaoli, YU Jijun 2015, 32(1): 27-32.  Abstract ( )   PDF (1573KB) ( )   Hypersonic flows around a blunt body are studied with numerical simulation and theoretical analysis.Correlations between plasma prediction and gas components are obtained.It shows that it is Mach number which affects the peak number density of electrons.Numerical simulation agrees with theoretical analysis well.Differences between two gas models get greater as Mach number increases.The differences follow same trend at back taper with stagnation region.A 11-species chemical model should be applied to increase accuracy when reentry capsule flight at height of 60 km and Mach number is over 23.

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A Post-processing Method for Smoothed Particle Hydrodynamics Data LI Fupeng, WANG Jiwen, OU Mang 2015, 32(1): 33-39.  Abstract ( )   PDF (5020KB) ( )   A post processing method for smoothed particle hydrodynamics data is presented on basis of Delaunay triangulation.Pairing particle set in scope of each particle in flow field is confirmed,and then discretized by Delaunay triangulation on condition of present pairing particle set,which leads to a set of triangle elements with particles as nodes.At last non material units are filtered.Examples indicate that SPH result with complex boundary conditions and severe deformation of fluid region can be treated.

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A Spectral Element Model with Atmospheric Near Space Resolved (SEMANS) LIU Xiying, LIU Chunyan, YAO Shanshan 2015, 32(1): 40-50.  Abstract ( )   PDF (4377KB) ( )   A numerical model,which solves equations with spectral element method and resolves atmospheric near space,is developed.Model validations are performed.The spectral element model with atmospheric near space resolved (SEMANS) is integrated for 10 years under configuration of 81 local elements in each projected face of cubed sphere with spectral approximation of 8th degree Gauss-Lobatto-Legendre interpolation polynomial and 66 vertical layers with top layer pressure 4.5×10-6 hPa.Through verification against ERA-Interim reanalysis dataset from ECMWF (European Center for Medium-Range Weather Forecasts) and COSPAR (Committee on Space Research) international reference atmosphere 1986,it is found that SEMANS reproduces features of 2 wave-lengths pattern along zonal circle in the northern hemisphere and 1 wave-length pattern along zonal circle in the southern hemisphere at 30hPa;SEMANS reproduces zones of low temperature at about 100 hPa,0.001 hPa and high temperature at about 1 hPa,above 0.0001 hPa;SEMANS also reproduces main features of zonal mean zonal wind in January and July below 0.001 hPa level.

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Shale Gas Seepage Mechanism and Transient Pressure Analysis DU Dianfa, WANG Yanyan, FU Jingang, SUN Zhaobo, QIAO Ni 2015, 32(1): 51-57.  Abstract ( )   PDF (1352KB) ( )   According to characteristic of shale gas reservoir,mathematical description methods of diffusion and desorption are analyzed.Three seepage models controlled by different kinds of seepage mechanisms are built:① a mathematical model which considers diffusion and interporosity of desorbed gas and free gas,② a mathematical model which considers desorption and diffusion,③ a mathematical model which considers desorption and diffusion in organic porosity and interporosity in inorganic porosity.With modified Lord Kelvin point source function pressure solutions are botained.With corresponding transformation for point source functions,formation pressure solutions for vertical fractured well and fractured horizontal well are obtained and typical curves are shown.At last,characteristics of different curves and three mechanisms' influences on pressure are analyzed.

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Mathematical Model and Numerical Simulation of Foam Plug Removal WANG Fei, LI Zhaomin, LI Songyan, DU Qingjun 2015, 32(1): 58-64.  Abstract ( )   PDF (1363KB) ( )   With a model of foam wellbore flow and a model of foam seepage flow,a mathematical model of foam plug removal is given.The model is solved with numerical method.Distributions of foam pressure,foam quality,foam density along wellbore and wellhead and bottom pressure are discussed.Furthermore,variation of bottom hole differential pressure is given as wellhead back pressure is fixed.It shows that as foam pressure and density increases,foam quality decreases with increase of well depth and bottom hole differential pressure declines.

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Influence of Femtosecond Laser Chirp on Optical Limiting and Dynamical Two-photon Absorption of 4,4'-bis (di-n-butylamino) stilbene Compounds ZHANG Yujin, ZHANG Qiuyue, SONG Yuzhi, WANG Chuankui 2015, 32(1): 65-74.  Abstract ( )   PDF (2037KB) ( )   Optical limiting (OL) and dynamical two-photon absorption (TPA) of 4,4'-bis(di-n-butylamino)stilbene (BDBAS) molecules in chirped femtosecond laser pulses are studied by solving Maxwell-Bloch equations with an iterative predictor-corrector finitedifference time-domain (FDTD) method.It shows that both sign and magnitude of chirp rate influence greatly spectrum evolution and OL behavior.Spectra exhibit obvious carrier frequency shifts depending on sign of chirp rate,blue shift for positive chirp rate and red shift for negative chirp rate.As absolute chirp rate increases,shift becomes more obvious,OL window gets narrower and saturation of output intensity becomes greater.Interestingly,self-induced transparency (SIT) appears as a negative chirp rate reduces to a certain value (-0.025 fs-2).Dynamical TPA cross section is reduced as chirp effect is considered.It provides a method for controlling nonlinear optical absorptions.

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Effect of Atomic Density on Propagation and Spectral Property of Femtosecond Gaussian Pulses WANG Zhendong, YANG Shanying, LIU Tingting, MA Jianling, XIAO Jing 2015, 32(1): 75-85.  Abstract ( )   PDF (4297KB) ( )   We investigate effect of atomic densities (N) on propagation and spectral property of femtosecond Gaussian pulses in a three-level Λ-type atomic medium by using numerical solution of full Maxwell-Bloch equations.It is shown that,for pulses with smaller area 2π,propagate in mediums with different N,pulse splitting does not occur and strength of spectral component near central frequency decreases considerably as N increases.For pulses with area 4π,pulse splitting could occur when pulses propagate in dilute medium with greater atomic density and in dense medium,and pulse spectral bandwidth and strength of spectral component with higher frequency increase with increasing of N in dilute medium.Spectrum broadening in dense medium is much smaller than that in dilute medium with greater atomic density.For pulses with larger area 8π,pulse splitting is similar to that of 4π pulses.Pulse spectral bandwidth and strength of spectral component with higher frequency increase monotonously with increasing of N.And spectrum broadening in dense medium is much larger than that in dilute medium with smaller atomic density.

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Intrinsic Energies of Two-dimensional Heisenberg Magnets and Ferromagnetic Single-walled Nanotubes MI Binzhou, FENG Cuiju, QI Yunping, DING Dong, XUE Yonghong 2015, 32(1): 86-92.  Abstract ( )   PDF (1931KB) ( )   Intrinsic energy of two-dimensional square lattice single-ion anisotropic Heisenberg ferromagnets,antiferromagnets,and ferromagnetic single-walled nanotubes are calculated with many-body Green's function method in quantum statistical theory.Calculated results of ferromagnets and antiferromagnets are compared.Between zero temperature and phase transition point,including zero temperature,anti-ferromagnetic energy is always lower than that of ferromagnetic energy.Calculation method of intrinsic energy in this paper is applicable not only to ferromagnetic system,but also suitable for antiferromagnetic system and ferrimagnetic system,as well as ferromagnetic single-walled nanotubes.Intrinsic energies are greatly lower than classical energies, which shows that transverse correlation effect is important.

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Magnetic Properties of Single-wall ZnS Nanotubes Doped with Fe Atoms XIE Jianming, CHEN Hongxia 2015, 32(1): 93-100.  Abstract ( )   PDF (2467KB) ( )   Magnetic properties of single-wall ZnS nanotubes (NTs) doped with Fe atoms are studied with first-principles calculations.Formation energies of doped NTs are smaller than that of pristine one,which indicating that doping is an exothermic reaction.Monodoped NTs has atom-like magnetic moments mainly due to 3d component of Fe atoms.It indicates that Fe-doped ZnS NTs tend to adopt antiferromagnetic (AFM) configurations.To obtain room temperature ferromagnetism,we replaced an S atom by a C atom and found that C atom prefers to substitute S atom connecting two Fe atoms.Ferromagnetic (FM) state energy is lower than that of AFM state by 164 meV.It implies that room temperature ferromagnetism is expected in these systems.

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Nonzero-point Casimir Force Between Nano Devices FANG Ming, SONG Kaihong, WANG Juanjuan, HUANG Zhixiang, WU Xianliag 2015, 32(1): 101-106.  Abstract ( )   PDF (1786KB) ( )   A frequency domain electromagnetic algorithm boundary element method is applied for computation of Casimir forces between arbitrary materials with arbitrary geometry.Considering electric and magnetic surface current distributions,Casimir force of two objects in terms of interactions of surface currents is obtained.Casimir effects between dielectric objects embedded in dielectric fluid are presented and numerical conditions of repulsive Casimir force are investigated.Non-zeropoint energy Casimir force calculation method is provided.It can be used for design of realistic MEMS.

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Electronic Structure and Magnetism of BaTi_2Bi_2O WANG Guangtao, ZHANG Lin, ZHANG Huiping, LIU Chang 2015, 32(1): 107-114.  Abstract ( )   PDF (4250KB) ( )   Electronic structure and magnetic structures of BaTi2Bi2O are studied with first-principles calculations.In nonmagnetic state,density of states at Fermi level are mostly derived from dz2,dx2-y2 and dxy orbitals.Fermi surface (FS) consists of three sheets.The third FS sheet (along X-R line) nests with the first FS sheet (along M-A line) by q-vector q1=(π/a,0,0) or q2=(0,π/a,0) shift.Calculated bare susceptibility χ0(q) peaked at X-point,rather than at M-point in Fe As-based superconductors.Such peaked susceptibility induces spin density wave (SDW).Magnetic ground state is nearly two degenerate antiferromagnetism of bi-collinear antiferromagnetism (AF3) and blocked checkerboard antiferromagnetism (AF4).Peak of susceptibility χ0(q) is obviously suppressed and becomes slightly in-commensurate with hole doping,but increased with electron doping.As spin fluctuation is suppressed superconductivity appears.It explains that superconductivity appears only in hole-doped compounds,and not in electron-doped ones.

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Performance of Asymmetric Linear Doping Triple-material-gate GNRFETs WANG Wei, GAO Jian, ZHANG Ting, ZHANG Lu, LI Na, YANG Xiao, YUE Gongshu 2015, 32(1): 115-126.  Abstract ( )   PDF (3490KB) ( )   Ballistic performance of single-material-gate and triple-material-gate graphene nanoribbon field effect transistors (GNRFETs) with various doping profiles is studied in a quantum kinetic model based on non-equilibrium Green's functions (NEGF) solved self-consistently with Poisson's equations.It shows that triple-material-gate GNRFET with linear doping (TL-GNRFET) exhibits significant advantage in reducing SCEs and DIBL effects,as well as achieving better subthreshold slope and better on/off current ratio.In addition,asymmetric gate underlap is also discussed.It is revealed that as top and bottom gates are both shifted towards source on/off state current performance is improved.