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25 September 2012, Volume 29 Issue 4 Previous Issue    Next Issue

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An Adaptive Two-level Preconditioner for 2-D 3-T Radiation Diffusion Equations ZHOU Zhiyang, XU Xiaowen, SHU Shi, FENG Chunsheng, MO Zeyao 2012, 29(4): 475-483.  Abstract ( )   PDF (1392KB) ( )   Performance of physical-variable based coarsening two-level(PCTL) preconditioner is analyzed for typical linear systems discretizated from two-dimensional(2-D) radiative diffusion equations with photon,electron,ion temperatures(3-T).It reveals that performance of PCTL strongly depends on both coupling of three temperatures and diagonally dominance of three diagonal sub-matrices of coefficient matrix.An adaptive algorithm for sub linear systems in PCTL is proposed.Numerical results show efficiency and robustness of the method.For 37 2-D 3-T linear systems in simulations,PCTL based on the algorithm speeds up 2.5 times compared with classical algebraic multigrid (AMG) preconditioners.

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Parallel Algorithm of Coupled Fourier Transform and Fluid Numerical Computation HU Xiaoyan, CAO Xiaolin, GUO Hong, CHEN Jun 2012, 29(4): 484-488.  Abstract ( )   PDF (1156KB) ( )   For parallel computation,two techniques are proposed to couple Fourier transform and fluid dynamics.One is muiti-physics coupled communication technique and the other is parallel Fourier transform.By comparing efficiency of the two techniques,it is shown that the muiti-physics coupled communication technique is better than calling parallel FFTW technique as the number of cores is relatively small,while calling parallel FFTW technique is better as the number of cores is over a thousand.Scalability is demonstrated with a parallel efficiency above 50% on 16 384 processors.Numerical simulation on laser filamentation is shown.

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High-Order Numerical Simulation of Vortex Breakdown on Delta Wing WANG Guangxue, DENG Xiaogang, WANG Yuntao, LIU Huayong 2012, 29(4): 489-494.  Abstract ( )   PDF (2109KB) ( )   With a fifth-order weighted compact nonlinear scheme(WCNS-E-5),flow field of a 65° delta wing with sharp leading edges at high angles of incidence is simulated.The target is checking WCNS's ability for vortex flow at high angles of incidence and vortex breakdown location with shock-vortex interaction.We focus on sudden jump in breakdown towards apex.Unsteady Reynolds averaged Navier-Stokes(URANS) method is available including a high-order weighted compact nonlinear scheme and an SST turbulence model.It is shown that the high order scheme(WCNS-E-5) with minimum numerical dissipation and could capture discontinuities for high angles of incidence transonic flow of delta wing and the results are matched satisfactorily with experiments.Shock-vortex interaction in transonic freestream explains sudden movement of vortex breakdown as the angle of incidence is increased.

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Numerical Simulation of Explosive Dust Detonation with CE/SE Method DONG Hefei, HONG Tao, ZHANG Xiaoli 2012, 29(4): 495-502.  Abstract ( )   PDF (1647KB) ( )   Two-phase detonation of RDX particles suspended in air was numerically studied with CE/SE method.Behind leading shock front of detonation,explosive particles are accelerated and heated by the gas flow.Energy is released to support propagation of detonation wave.Dust detonation in a shock tube was numerically simulated.Distribution of physical quantity behind leading shock front was calculated.Parameters of detonation were obtained and they agree well with those in a reference.Dust detonation in a complex channel was numerically simulated.It shows that CE/SE method simulates gas-solid two-phase detonation successfully.

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A Method for Velocity Calculation of Nanoflows QI Zhenhong, ZHANG Wenfei, JIA Min 2012, 29(4): 503-510.  Abstract ( )   PDF (3999KB) ( )   A method is developed with a relationship between volume of fluid and velocity and molecular dynamics method.Flow velocity of liquid argon is calculated in simulations of three-dimensional Poiseuille flows and cavity flows.It shows that calculated flow velocities are basically consistent with that obtained from traditional molecular dynamics method.The method can be applied to various kinds of channel flows.For flows driven in square cavities,calculated velocities are roughly the same,but the boundary velocities are varied widely.Accuracy of the new method is better with a faster convergence rate.

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Brownian Dynamic Simulation of Sludge Perikinetic Flocculation with Ionization LIU Linshuang, YANG Guolu, YU Minghui 2012, 29(4): 511-518.  Abstract ( )   PDF (2199KB) ( )   A Brownian dynamic simulation of perikinetic flocculation of fine sediment with ionization is presented.Langevin equation is used as dynamical equation in tracking particles in a floc.Monte Carlo method is used in simulating random variation in particle movement.Sludge particles are supposed in uncharged and charged state in dispersion system.Electrostatic force on a particle in a simulation cell is considered as a sum of electrostatic force from other particles in the original cell.Particle initial place is decided by particle diameter and sludge density.Particle initial velocity is determined by Gauss random distribution.Effects of particle diameter and sludge density on flocculation and floc structure are discussed.On the other hand,effects of electrostatic force on flocculation are presented.The model proposed coincide well with practical situations.

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A Mathematical Model of Foam Flooding Based on Foam Microscopic Seepage Characteristics LU Teng, LI Zhaomin, LI Jing, LI Ran 2012, 29(4): 519-524.  Abstract ( )   PDF (1598KB) ( )   Foam microscopic seepage experiments show that foam present two seepage states: Flowing foam and trapped foam.Foam plugging experiment show that foam plugging ability has accumulating effect.Plugging pressure gradient near core inlet is less than that of downstream of the core when foam flooding reaches steady state.A multi-component mathematical model characterizing foam flooding is established based on bubble population balance theory and foam properties.The model is solved numerically with fully implicit method.Validity of the model is verified with foam plugging experiment.Meanwhile,foam microscopic seepage characteristic parameters such as foam texture,pressure and aqueous phase saturation in foam flooding are studied.

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SPH Method in Numerical Simulation of Liquid-Solid Impact WANG Anwen, XU Fei, ZHANG Yueqing 2012, 29(4): 525-533.  Abstract ( )   PDF (3571KB) ( )   Two methods(SPH and ALE) are used to simulation of droplets impacton PMMA.Deformation of droplets and failure of PMMA are compared.It shows that the surface failures in two methods agree with Brunton's experiment.Feasibility and accuracy of two methods are proved.SPH method shows better ability in simulating liquid-solid impact.Then,a rain ball impact the edge of airscrew of a flying aircraft is analyzed with SPH method.Two engineering techniques are proposed to protect integrity of airscrew.

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Isogeometric Analysis on Eigenvalues of Waveguide with Arbitrary Cross-section ZHANG Yong, LIN Gao, HU Zhiqiang, LIU Jun 2012, 29(4): 534-542.  Abstract ( )   PDF (1780KB) ( )   Isogeometric analysis(IGA) is applied to eigenvalue problem of waveguide with arbitrary cross-section.Weakened equations are involved with NURBS elements from governing equation of waveguide.The computational model in IGA is inherited from a design model in CAD system,which is beyond traditional numerical method with remodeling procedure.Elliptical waveguides with various eccentricities,triangular and pentagon waveguides are addressed as numerical examples.It demonstrates that the preseut method is feasible for eigenvalue analysis of waveguide with either elliptical or polygonal cross-section.Moreover,it yields excellent results with fewer DOFs,and obtains quicker convergence than traditional method.

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Simulation of Magnetic Levitation Induction Heating of Metal Spheres with Anti-connected Coils ZHANG Jicheng, TANG Yongjian, LUO Jiangshan, WU Weidong 2012, 29(4): 543-548.  Abstract ( )   PDF (1627KB) ( )   A model of electromagnetic force and temperature field in magnetic levitation induction heating is studied.Influence of electric current,anti-connected coils,metal sphere positions on heating and temperature distributing of metal spheres are analyzed,as well as electromagnetic force.Simulation results are confirmed with experiments.

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Helix Buckling of a Slender Rod in Inclined Cylinder: Analysis with Euler-Rodrigues Parameters YUAN Zhangxian, WANG Xinwei 2012, 29(4): 549-556.  Abstract ( )   PDF (1758KB) ( )   Post-buckling configuration of a slender rod constrained in a cylinder is described with Euler-Rodrigues parameters.Corresponding energy function is obtained.Nonlinear differential equilibrium equation and contact force are established through the energy function.The problem is solved successfully with finite element method.To verify the formulations and solutions,comparisons with existing data or solutions are made.Numerical results revealed conversion process from sinusoidal buckling to helix buckling.Possibility of mode changing in post-buckling process is verified.

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A Fast Calculation Method for Optical Field in Unstable Laser Resonators ZHANG Xiao, LIU Wenguang 2012, 29(4): 557-565.  Abstract ( )   PDF (2256KB) ( )   Du Fort-Frankel differential format for mode calculation of unstable resonator is presented.A fast finite differential method based on matrix motion and coordinate system transformation is used to calculate output field of a bare cavity and an active cavity.Calculated results are compared with references.It shows that the method is good both in precision and speed in calculating modes of an active unstable resonator with large Fresnel numbers.It can be 20 to 40 times faster compared with a conventional method.With this method,output power of a HF chemical laser is calculated.It shows that the output power increase with decrease of distance between gain medium and concave mirror.This result is valuable to the design of high power DF chemical laser.

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High Precision Analytic Diatomic Molecular Potential Functions with Six Parameters YU Changfeng, WANG Zhiwei 2012, 29(4): 566-574.  Abstract ( )   PDF (1252KB) ( )   A method for constructing analytical diatomic molecular potential energy functions is proposed.The potential energy function is examined with 36 diatomic molecules or ions-homonuclear ground-state of neutral diatomic molecules Li2-X1∑g+,Na2-X1∑g+,heternuclear ground-state of charged diatomic molecular ion (BC)--X3∏,heternuclear excitation-state neutral diatomic molecules PbS-A1∑+,BaO-A1∑,heternuclear excitation-state of charged diatomic molecular ion (CS)+-A2∏,homonuclear excitation-state of neutral diatomic molecule K2-B1∏u,homonuclear excitation-state for charged diatomic molecule N2+-B2∑u+ etc.Vibrational energy levels of molecules calculated are consistent with RKR data (Rydberg-Klein-Rees) and experimental data in high-precision.It shows that the potential energy function is superior to Murrell-Sorbie potential in calculating vibrational energy levels of molecules.

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A Calculation Method for Semi-classical Model of Carbon Nanotube Field Effect Transistors ZHAO Xiaohui, CAI Li, ZHANG Peng 2012, 29(4): 575-579.  Abstract ( )   PDF (690KB) ( )   Newton-Raphson iteration is used in semi-classical model of carbon nanotube field effect transistors(CNTFET) based on ballistic transport for self-consistent potential.In each iteration re-integration of state density is requred.Support vector regression (SVR) is applied for the relationship of self-consistent potential and carrier density.Numerical integrations are avoided.And gradient descent algorithm (GDA) is used to get self-consistent potential.It shows that compared with Newton-Raphson iteration,the proposed method reduces computation effectively while maintains high accuracy.It lays theoretical foundation for designing and applying CNTFET devices in large scale integrated circuits.

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A Thermal Model for Top Layer of Three-dimensional Integrated Circuits with Through Silicon Via WANG Fengjuan, ZHU Zhangming, YANG Yintang, WANG Ning 2012, 29(4): 580-584.  Abstract ( )   PDF (3613KB) ( )   With through silicon via(TSV) area scale factor r,an analytical thermal model for top layer of three-dimensional integrated circuits(3D IC) taking TSV into account was proposed.It is shown that temperature is lower after considering TSVs under same working conditions;the greater the scale factor r,the lower the temperature is;For more layers and smaller r,temperature increases sharply with decrease of r;The best range of TSV area ratio factor r is 0.5% to 1% for an 8-layer 3D IC.

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Inelastic Electron Tunneling Spectroscopy of Molecular Junctions with Metal Electrodes LENG Jiancai, ZOU Bin, MA Hong, LI Wei 2012, 29(4): 585-592.  Abstract ( )   PDF (2206KB) ( )   First-principles investigation on inelastic electron tunneling spectra of 1,6-hexanedithiol and 1,4-benzenedithiol molecular junctions with metal electrodes are performed.It shows that vibrational peaks in inelastic electron tunneling spectra are sensitive to electrode material and distance between sulfur atoms and electrodes.It hence provides unambiguous evidence that electrode material and metal-molecule bond length are crucial for inelastic electron transport through molecular junctions.The peak heights are mainly attributed to coupling energies between electrode and molecule.

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First-Principles Study of Electronic and Optical Properties of N-S Co-doped Rutile TiO2 FENG Qing, WANG Yin, WANG Weihua, YUE Yuanxia 2012, 29(4): 593-600.  Abstract ( )   PDF (2567KB) ( )   Band structures,density of states and optical properties of pure,N-doped,S-doped and N-S co-doped rutile TiO2 are studied with plane-wave ultrasoft pseudopotential method based on first-principles density functional theory.It shows that the gap of N-doped TiO2 reduces to 1.43 eV,and there is an impurity band on top of the valence band.S-doped TiO2 results in Fermi level moves to the conduction band,and the gap decreases to 0.32 eV.N-S co-doped TiO2 results in two impurity bands located in the band gap.One impurity band is apart from the bottom of conduction band by 0.35 eV,the other is apart from the top of valence band by 0.85 eV,which is mainly formed by N-atom 2p orbital and S-atom 3p orbital.It causes a red-shift in absorption wavelength,and gives rise to extremely great absorption coefficient in visible-light region,which shows a strong photocatalytic activity.

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Structure and Stability of Medium-sized ZnS Clusters CHEN Hongxia, WANG Baolin 2012, 29(4): 601-610.  Abstract ( )   PDF (3306KB) ( )   Structure and stability of medium-sized (ZnS)n (n=24,28,36,and 48) clusters are investigated by using first-principles approaches.A number of starting configurations for structural motifs were generated from handmade construction with chemical intuition and cut from bulk crystal.They are optimized via density functional theory(DFT).For medium-sized ZnS clusters,cage and tube structures were found the most preferred structural motifs.With increasing size,onion-like structures became more and more stable,which indicating that they are the lowest-energy structures for larger-sized clusters.Furthermore,it shows that WZ bulklike structures are more stable than ZB bulklike structures in medium-sized ZnS clusters.

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Structure of Small Nin (n≤8) Clusters YAN Shiying, JIANG Hai 2012, 29(4): 611-619.  Abstract ( )   PDF (925KB) ( )   Density functional theory B3LYP are performed in study on structure of Nin,Nin+ and Nin-(n=2-8).DGDZVP all-electron basis sets and TZVP all-electron basis sets are employed. Equilibrium geometries, ionization potentials,electron affinities and binding energies are obtained.It shows that the ground state of Ni2,Ni3,Ni4,Ni5 and Ni6 cluster are 5-,7-,9-,11-,and 13-multiple state,respectively,which indicates spin polarization effect in Nin (n≤8 )clusters is important.That is,there are 4,6,8,10,and 12 parallel spin electrons iu Ni2,Ni3,Ni4,Ni5 and Ni6 cluster,respectively.Number of non-conjugated electrons in ground state cluster is the greatest.These electrons occupy different spacious orbitals so that energy of Nin (n≤8) cluster is minimized.It can be concluded that effect of parallel spin in Nin (n≤8) clusters is greater than effects of conjugated clusters,which is obviously related to electron d delocalization.This is spin polarization effect of Nin (n≤8) clusters,which is a result of the Hund' s rule.Moreover,we find that spin magnetic moments of Nin(n=6-8) are 8 μB,those of Nin+(n=6-8) are 9 μB and those of Nin-(n=4-10) are7 μB.

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Effect of Lévy Noise and Periodic Force on Dynamics of Spiral Waves CHEN Shaoying, YUAN Guoyong, WU Gang, CUI Qianqian, FAN Hongling 2012, 29(4): 620-626.  Abstract ( )   PDF (2162KB) ( )   We study effect of additive Lévy noise and periodic force on dynamics of spiral waves,which appears in a FitzHugh-Nagumo excitable system.Motion of spiral tip changes regularly with external force period in domains,which can be explained with corresponding Fourier spectrum.A regular change is due to the existence of frequency-locking.Lévy noise sequence contains large-scale noise with a small probability.Large-scale noise has main effect on the motion of spiral tips.We pointed out that effect of Lévy noise on tip motion depends on period of external force.At appropriate parameters,the Lévy noise leads to the disappearance of spiral waves,and it offer a methold of controling and eliminating spiral waves.The locking behavior between internal period of the system and external modulation period is analyzed.Arnold tongues is obtained at various noise intensities.They indicate existance of stochastic resonances.

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Tangential Force Distribution in Granular System with Composition Disorder ZHANG Xinggang, HU Lin 2012, 29(4): 627-632.  Abstract ( )   PDF (2124KB) ( )   Discrete element method is used to study probability distribution of tangential forces in granular system with composition disorder.Primary tangential force and secondary tangential force are distinguished and their statistics are analyzed separately.As the rate of defects increases,tangential force distribution transforms from approximate normal distribution to a distribution with two peaks.Finally it becomes a distribution with one peak.Whereas secondary tangential force distribution is always exponential.It shows that force distribution of composition disorder with great defect rate and structural disorder are similar.