Archive

25 November 2012, Volume 29 Issue 6 Previous Issue    Next Issue

---

For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Select

A Second Order Lagrangian Scheme Based on Characteristics Theory for Two-dimensional Compressible Flows SUN Yutao, JIA Zupeng, YU Ming, REN Yuxin 2012, 29(6): 791-798.  Abstract ( )   PDF (743KB) ( )   We present a second order cell-centered finite volume method of 2D Lagrangian hydrodynamics based on semi-discrete framework.Velocity and pressure on vertex of a cell are computed with characteristics theory,Then,they are used to compute numerical flux through cell interface by trapezoidal integration rule.With a reconstruction procedure,the method is extended to second order.Several numerical experiments confirm convergence and symmetry of the method.The method permits large CFL numbers and can be applied on structured and unstructured grids.It is robust in multi-material flow simulations.

Select

Three Boundary Particulate Flows in Treatment Schemes for Lattice Boltzmann Method HUANG Rongzong, WANG Liang, GUO Zhaoli 2012, 29(6): 799-806.  Abstract ( )   PDF (757KB) ( )   A detailed comparative study is made to investigate three boundary treatment schemes in lattice Bohzmann methods (LBM).They are half-way bounce back scheme,sub-grid scheme,and a scheme to treat curved boundaries.It is found that particle translational and angular velocities calculated with half-way bounce back scheme oscillate strongly,while particle velocities obtained by sub-grid scheme evolve smoothly.

Select

Wall Heating and Adaptive Heat Conduction Viscosity SHEN Zhijun, XIE Yawei, YAN Wei 2012, 29(6): 807-814.  Abstract ( )   PDF (923KB) ( )   A numerical scheme and method deducing "wall heating errors" in computing problems of radially symmetric flow using Lagrangian cell-centered schemes is investigated.Relation between "wall heating error" and modified equations of difference schemes is introduced.With comparision of sound wave approximate Riemann solver and HLL Riemann solver,a new adaptive heat conduction viscosity is introduced to ameliorate "wall heating errors".Numerical experiments show that this viscosity in current scheme provides satisfactory results.

Select

Mathematical Model for Two-phase Flows in a Proton Exchange Membrane Fuel Cell with Straight Flow Channels LIU Xunliang, LOU Guofeng, WEN Zhi 2012, 29(6): 815-822.  Abstract ( )   PDF (914KB) ( )   A non-isothermal three-dimensional(3 D) two-phase flow transport model is developed for a proton exchange membrane fuel cell(PEM FC) with straight flow channels.Based on characteristics of water transport between membrane and gas phase,a non-equilibrium model is developed for liquid water transport in membrane,considering electroosmosis,concentration diffusion and electrochemical reaction.A finite volume method is used to discretize governing equations and solution code is developed.The model is used to simulate multi-physical field coupled transport in a PEMFC.Investigations are performed for water vapor concentration,liquid water saturation,membrane water content distribution and liquid water transport velocity.Temperature field inside a cell and predicted polarization are obtained.

Select

Front Tracking for Moving Boundary of Non-Darcy Seepage Flows in Low-permeability Porous Media LIU Wenchao, YAO Jun, WANG Jianzhong 2012, 29(6): 823-827.  Abstract ( )   PDF (418KB) ( )   Based on a mathematical model of non-Darcy unsteady seepage flows in low-permeability porous media with moving boundary conditions,a differential equation of propagation velocity for moving boundary was deduced.It indicates that propagation velocity of a moving boundary is proportional to the second derivative of formation pressure with respect to radial distance on the moving boundary.And with Lagrange three-point interpolation formula,finite difference scheme of governing equation near a moving boundary was obtained.Exact position of a moving boundary is able to be tracked.Numerical results show that the front tracking method describes propagation behaviors of moving boundary of non.Darcy unsteady seepage flows in low-permeability porous media well.

Select

Schemes for Interpartical Interaction Forces in Multiphase Shan-Chen Model HU Anjie, LI Longjian, ZENG Jianbang 2012, 29(6): 828-836.  Abstract ( )   PDF (658KB) ( )   A single-component multiphase lattice Boltzmann model which combines effective mass function with special potential in calculating interparticle potential based on Shan-Chen model is proposed.Accuracy of the model is verified by simulating single-component phase change process.Different equations of state are explored in the model.It shows that the model has many advantages: It tallies with the Maxwell construction more precisely;The maximum magnitude of spurious current is smaller and the range of simulation temperature is greater.Laplace tests is carried out and simulated results are in conformity.

Select

Calibration Parameters in Non.Guassian 0ne.factor Short-term Rate Model with Regularization Method JIANG Liang, XU Chenglong 2012, 29(6): 837-844.  Abstract ( )   PDF (579KB) ( )   Basing on regularization method,we propose an efficient method for calibrating time-varying parameters in non-Gaussian one-factor short-term rate model with constraineds.Stability and convergence are proved with variational principle。For computational convenience,penalty method and smoothing operator are applied to transform a constrained inverse problem into one without constraints.Finally,theoretical analysis is shown valid by means of numerical simulations.Empirical results is earried out.

Select

Improved Algorithm Based on Sliced Sensitivity for Three.dimensional MREIT LI Gang, CHEN Ruijuan, HAO Liling, ZHOU Mei, LIN Ling 2012, 29(6): 845-852.  Abstract ( )   PDF (1138KB) ( )   An improved sliced sensitivity reconstruction algorithm is proposed for three-dimensional(3D) magnetic resonance electrical impedance tomography(MREIT).Using single component of magnetic flux density measured by a MR scanner,all slices are reconstructed respectively with a modification for 3D conductivity images.Simulation of a cubic model shows that the proposed algorithm improves interlayer crosstalk phenomenon with a higher image resolution than sliced reconstruction without modification and entire reconstruction algorithm.Computing time is significantly reduced.Simulation on a human leg model shows feasibility for complex imaging objects.Phantom results verify reconstruction algorithm in real measurements.The improved sliced sensitivity reconstruction algorithm reduces requirements for computer capability and reconstruction time of 3D MREIT with high imaging precision and efficiency.

Select

Periodic Symmetric R-FDTD Method and Reducing Optimization LIU Lina, ZHU Feng, XU Changwei, NIU Dapeng 2012, 29(6): 853-858.  Abstract ( )   PDF (476KB) ( )   Necessity for calculating boundary temporary field components in reduced finite-difference time-domain method(R-FDTD) is discussed.A periodic symmetric R-FDTD method is proposed.Temporary components in supplement calculation are given based on symmetry and periodic boundary conditions(PBC).Computational domain is reduced to 1/4 and lateral field components of a symmetry plane are obtained with symmetry relations.Compared with original FDTD,memory storage is reduced to 1/6 while ensuring accuracy. It is shown that the improved algorithm agrees with FDTD method by numerical simulation of EM impulse responses tO infinity wire mesh reinforcement and reinforced concrete layer.The improved algorithm has advantages in saving memory storage and calculation time.

Select

Numerical Study on Collision Effect in Magnetized ElectronegatiVe Plasma Sheath with Two Species of Positive Ions ZHAO Xiaoyun, ZHANG Bingkai, WU Shan, LI Shigang 2012, 29(6): 859-866.  Abstract ( )   PDF (934KB) ( )   A fluid model is developed in magnetized electronegative plasma sheath with two species of positive ions.It is shown that one-dimensional stationary plasma sheath is affected by ions-neutral collisions.The range of ion Mach numbers depends on density ratio of Ar+ to He+ and collision parameter. Collision efkct on charge density in the sheath is obvious as density of negative ions is small. Density of electron and negative ion decreases quickly.Two kinds of positive ion density present different fluctuations.Collision effect on ion velocitv distribution in the sheath is obvious as density of negative ions is great. In addition,collision paramcte affects density distribution of charge particles clearly as density ratio of two species of positive ions is great.

Select

Dynamics Simulation of SF6 Discharge in a Short Gap Under Uniform Electric Field ZHENG Dianchun, XIA Yunshuang, ZHU Shihua, WANG Wenlong, ZHAO Dawei 2012, 29(6): 867-875.  Abstract ( )   PDF (1147KB) ( )   With fundamental physical laws and fluid mechanics,a discharge fluid model of SF6 in a short gap under uniform field is established.Flux-corrected transport(FCT) technique is used in numerical simulation of SF6 discharge at atmospheric pressure. Dynamic characteristics of charged particles,distributions of gap-space electric field and evolutions of discharge channel are revealed. Tempo-spatial critical point of avalanche-to-streamer is discovered and shown.It shows that photoionization plays an important role in streamer development stage.

Select

Stray Light Analysis Based on Domain Decomposition and Staged Ray Splitting CHEN Xue, SUN Chuang, XIA Xinlin 2012, 29(6): 876-880.  Abstract ( )   PDF (788KB) ( )   A technique combined domain decomposition and staged ray splitting is presented to decrease computational complexity by reducing surfaces and rays for intersections solution.Domain decomposition is based on relation between sub-zone and number of surfaces.Splitting ratio is determined with propagation information of stray light.A suppression structure and a multi-sensor system are analyzed.It shows that the technique can improve computational efficiency while maintaining acceptable accuracy.

Select

Phase Correlation in Propagation Effect of a Doppler Broadening Quasi-Λ Type Four-level System LIU Zhongbo, FAN Xijun 2012, 29(6): 881-890.  Abstract ( )   PDF (1084KB) ( )   Influence of relative phase between probe and driving fields(Φ) Oil propagation effect of a Doppler broadened quasi-Λ type four-level atomic system with spontaneously generated coherence(SGC) is numerically studied.It is shown that by choosingΦ, we can obtain greater GWI and longer propagation distance where GWI exists and hence obtain higher LWI intensity.Doppler broadening width and propagation directions of probe and driving fields have considerable effect on phase·dependent spatial evolutions of GWI and LWI intensity.

Select

An Unfolding Method of NDP Based on Probability Iteration YANG Xin, LI Rundong, LIU Hangang, WANG Guanbo, WANG Kan 2012, 29(6): 891-900.  Abstract ( )   PDF (1023KB) ( )   For NDP,we produce an iteration method derived from probability iteration.It is compared with linear regularization(LR) method for unfolding of NDP.Both produce good results without counts random errors.Iteration method's result is none-negative.LR method is better at the position where source distributions change steeply.Iteration method produce better results as we consider count random errors.It shows that amplifying matrix elements exponentially brings acceleration.

Select

Simulation on Crushing of Two-dimensional Grains WANG Zhenhui, YANG Xianqing, CHEN Qiong 2012, 29(6): 901-905.  Abstract ( )   PDF (589KB) ( )   A single-particle breakage model is constructed with material mechanics.Fragmentation of two-dimensional grains under applied pressures is simulated with molecular dynamics.It demonstrates that ultimate grain size distributions follow a power-law distribution with a fractal dimension of about 1.1,which indicates that fragmentation processe of two-dimensional grains is a fractal process.

Select

Theoretical Study on Reaction Between Mg(NH2)2 and LiH CHEN YuHong, DONG Xiao, LV Xiaoxia, ZHANG Meiling, ZHANG Cairong, KANG Long, LUO Yongchun 2012, 29(6): 906-912.  Abstract ( )   PDF (856KB) ( )   Rcaction mechanism between Mg(NH2)2 and LiH are investigated with a B3LYP method of density functional theory. Geometries and harmonic vibration frequencies of reactants,intermediates,transition states and products are calculated at B3LYP/6-311G(d,P) level.Vibration analysis and intrinsic reaction coordinates(IRC) calculation at the same level are applied to validate connection of stationarv points. It indicates that the reaction has three stages.They are the first step of hydrogen substitution,the second step of hydrogen substitution and isomerization after removal of hydrogen.There are two pathways, in which a channel of the second step of alignment hydrogen suhstitution reaction is the main channel.The two hydrogen atoms in H2 released are from Mg(NH2)2 and Lilt.

Select

Theoretical Study of Molecular Orbital Energy Levels and Aromaticity ofWnNim(n+m=8)clusters ZHANG Xiurong, LI Yang, YIN Lin 2012, 29(6): 913-920.  Abstract ( )   PDF (828KB) ( )   Possible equilibrium geometries of WnNim(n+m=8) clusters are optimized with density functional theory at B3LYP/LANL2DZ level.For ground state structures,molecular orbital energy level,HOMO level,LUMO level,aromaticity and thermodynamics are analyzed.It shows that molecular orbits between Alpha and Beta in clusters W5Ni3 and W6Ni2 are completely degenerate,and all electrons are strictly paired.W2Ni6 cluster,with low energy gap,has strong chemical activity.Its component for frontier orbital are basically the same.W6Ni2cluster,with high energy gap,has weak chemical activity;Clusters W1Ni7,W5Ni3,W6Ni2,W7Ni1 have aromaticity,while W2Ni6 cluster has antiaromaticity.Formation enthalpy of all clusters WnNim(n+m=8) are negative.They are stable Oil thermodynamics.

Select

Theoretical Study on Electronic Structure and Vibrational Spectrum of PtIrn0,±(n=1~5) Clusters GUO Wenlu, RAO Qian, ZHANG Xiurong 2012, 29(6): 921-930.  Abstract ( )   PDF (661KB) ( )   NBO,vibrational spectrum,aromatic characteristics and polarizability of ground state PtIrn0,±(n=1~5)clusters are analyzed by using density functional theory(b31yp).It shows that platinum atom gains charges during cluster growth,while some iridium atoms gain charges and others lose.They are transferred to platinum atom and other iridium atoms.More vibration peaks appear in IR and Raman sDectrums as more atoms are added. Vibration peaks of IR and Raman spectrum of Ptlr4- cluster are the strongest. PtIrl3、Ptlr5、PtIr5+ clusters are aromatic.Bond interactions between atoms present a rising tendency with the increase of atomic number-Electronic structures of PtIr3、Ptlrs5+ clusters are relatively unstable, and delocalization effects are strong. With the increase of atomic number,stability of electronic structure of anionic clusters presents a rising tendency,and delocalization effect decreases gradually.

Select

Resonance Modes of Coupled Trilayers with Stress Anisotropy RONG Jianhong, WANG Huan, YUN Guohong 2012, 29(6): 931-937.  Abstract ( )   PDF (687KB) ( )   Magnetic properties of ferromagnetic/ferromagnetic/antiferromagnetic trilayers with stress anisotropy are investigated by using ferromagnetic resonance method.Acoustic mode and optical mode are observed.As applied magnetic field in the plane of film.in some regions,with increasing stress anisotropy field resonance fields of acoustic and optical modes shift to higher values.With increasing ferromagnetic film thickness, the shift of acoustic mode resonance field is different. Furthermore.the resonance field of optical mode is irrelative with intensity of stress anisotropy.

Select

Temperature Characteristics of Three-dimensional Chip-multiprocessors WANG Fengjuan, YANG Yintang, ZHU Zhangming, WANG Ning, ZHANG Yan 2012, 29(6): 938-942.  Abstract ( )   PDF (602KB) ( )   An expression of thermal resistance matrix is given.Transient temperature characteristics of three-dimensional chip-muhiprocessors(3D-CMP) are studied.Effect of heat capacity,thermal resistance and power consumption on temperature is analyzed. It shows that steady temperature of 3D-CMP is limited effectively by reducing thermal resistance and power consumption.Heat capacity influences rise time of temperature.It does not affect steady temperature.

Select

Cascading Failures of Power Grids Under Three Attack Strategies LAN Qingyu, ZOU Yanli, FENG Cong 2012, 29(6): 943-948.  Abstract ( )   PDF (533KB) ( )   We study cascading failures of the western United States power grid under three attack strategies,Initial load of an edge ij is defined as(kikj)θ with kiand kj the degrees of nodes connected with the edge,where θ is a tunable parameter.Three attack strategies are LL(attack on edges with the lowest load),SPC(attack on edges with the smallest proportion between total capacities of neighboring edges and capacity of the attacked edge)and HL(attack on edges with the highest load).It is observed that cascading failure scales are quite different under three attack strategies with different θ.Analyzing topology of the power grid in detail,we study otherness of cascading failures under three attack strategies.It shows that select ranges of attacked edges are not varied with θ under strategies of HL and LL.Attack effect of HL is enhanced with increasing θ,however,attack effect of LL is weaken with increasing θ. Select ranges of attacked edges of SPC varies with θ.At a small θ,attacked edges of SPC are belong to LL with a special topology,As θ increased,attacked edges of SPC tend to those edges with relatively high loads.Consequently,attacked effect of SPC is close to that of LL with a small θ and it is close to that of HL with a great θ.