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25 July 2011, Volume 28 Issue 4 Previous Issue    Next Issue

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FFT Parallel Solver Based on JASMIN and Applications GUO Hong, CAO Xiaolin, HU Xiaoyan 2011, 28(4): 475-480.  Abstract ( )   PDF (1186KB) ( )   An FFT parallel solver is designed and implemented in JASMIN infrastructure to solve problems,such as computation scale restriction,great change of data structure,different communications among data structures,and arguments' diversity of FFTW functions as using FFTW directly.The solver encapsulates several distributed storages of data,different communications and 1D FFT computations with FFTW.It provides standard functions to users.With this solver FFT parallel computing is realized conveniently.It was used in numerical simulations of laser filament.Scalability was demonstrated with a parallel efficiency above 80% on 2048 processors.

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GPU-accelerated Boundary Element Method for Burton-Miller Equation in Acoustics HUANG Shuo, XIAO Jinyou, HU Yucai, WANG Tao 2011, 28(4): 481-487.  Abstract ( )   PDF (766KB) ( )   A boundary element method (BEM) for Burton-Miller boundary integral equation is accelerated efficiently with Graphics Processing Units (GPUs).Conventional BEM formulations are reformulated so that they can be handled efficiently in GPU.Singularity extraction and local correction techniques are used to evaluate singular integrals,including strong-and hyper-singular ones.Numerical results show that:(1)The proposed method obtains unique and correct solutions at fictitious frequencies;(2)Accuracy of the method is almost the same as that of conventional BEM;(3)Computational time and memory consumptions of the proposed method are much lower than reported results.It shows that GPU-accelerated BEM based on Burton-Miller equation is a fast,efficient and simple method for medium-or large-scale acoustic problems in engineering.

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Initialization Method in Three-layer Parallel Difference Scheme for Heat Equation ZUO Fengli, CUI Xia, YUAN Guangwei 2011, 28(4): 488-492.  Abstract ( )   PDF (238KB) ( )   An explicit method is proposed to initiate three-layer difference scheme for two-dimensional heat problems.Stability and convergence theorem is shown with a three-layer domain decomposition parallel difference algorithm with inner boundary prediction-correction and explicit initialization.Parallel numerical experiments show that the method is numerical stable,and is more convenient in program realization compared with usual implicit initialization method.It reduces numerical errors greatly compared with existing perturbation methods.

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An Effcient GAMG-based Preconditioner for Second Order Mixed-type Finite Volume Element Method ZHOU Zhiyang, NIE Cunyun, SHU Shi 2011, 28(4): 493-500.  Abstract ( )   PDF (377KB) ( )   Preconditioners for GMRES method are discussed in solving linear systems discretized from scalar elliptic partial differential equations of second order with jump coeffcient.Based on hierarchical basis,spectral equivalence is established for two kinds of stiffness matrices from quadratic finite element and second order mixed-type finite volume element method,respectively.A preconditioner is proposed by combining equivalence with two-level geometric-algebraic multigrid(GAMG) method which was especially designed for linear systems arising from quadratic finite element discretization.Numerical results confirm correctness of our theoretical analysis.It shows that the preconditioner is quite effcient and robust.

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Reconnection-based Lagrangian-local Remeshing Method for Large Deformations WANG Ruili, LIN Zhong, WEI Lan 2011, 28(4): 501-506.  Abstract ( )   PDF (686KB) ( )   We present a reconection-based Lagrangian+rezone(LR) method,in which connectivity of meshes can be changed in a rezone phase in order to handle geometric intersection.The method maintains more Lagrangian features of meshes than standard LR methods.Numerical examples demonstrate that the method is more robust for large defomations.It shows predictive capabilities of reconnection-based LR method.

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Numerical Simulation of a Sway Tank with Unstructured Grid High Order Scheme MING Pingjian, DUAN Wenyang 2011, 28(4): 507-514.  Abstract ( )   PDF (574KB) ( )   A method for simulation of a sway tank is presented,in which phase interface is treated as a physical discontinuity.The discontinuity is captured by a well-designed high order scheme.A numerical method for free surface flow on a fixed grid is established.This method is implemented in an in house code GTEA(General Transport Equation Analyzer) which is an unstructured grids finite volume solver.A classical dam break case and a two-dimensional rectangular sway tank at different excitation frequency are used to validate the method.The sloshing load on monitor points agrees well with experimental data.The method gives better results on the secondary peak compared with a commericial software CFX.It shows that the method simulates free surface overturning and breakup well.

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Simulation of 2D Channel-filling with Corrected SPH Method REN Jinlian, OUYANG Jie, JIANG Tao 2011, 28(4): 515-522.  Abstract ( )   PDF (1289KB) ( )   A corrected smoothed particle hydrodynamics(SPH) method is proposed,in which standard SPH method is corrected with a density re-initialization method.A treatment for solid wall boundaries is presented to improve numerical accuracy.Drop stretching and dam-breaking are simulated numerically to show validity and reliability of the method.Filling process in a channel is investigated,and effect of Reynolds number on flow field and vortex are analyzed.It shows that the corrected SPH method can simulate filling process in a channel precisely and the flow is affected significantly by Reynolds number.

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Simulation of Water Entry with Smoothed Particle Hydrodynamics Method YANG Xiufeng, PENG Shiliu, LIU Moubin 2011, 28(4): 523-528.  Abstract ( )   PDF (443KB) ( )   A modified Smoothed Particle Hydrodynamics(SPH) in Lagrangian-averaged Navier-Stokes-alpha(LANS-α) model was developed to simulate water entry flow.Water entry of a half buoyant cylinder and a neutrally buoyant cylinder were simulated.SPH results are in good agreement with reported experiments and numerical results of others.It shows that the modified SPH method is practicable in simulation of water entry flow.

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Contact Melting of Unfixed Solid Phase Change Material Inside a Cylindrical Tube with Constant Heat Flux ZHAO Yuansong, LIANG Weihua, CHEN Wenzhen 2011, 28(4): 529-534.  Abstract ( )   PDF (510KB) ( )   Melting of unfixed solid phase change material(PCM) inside a cylindrical tube was investigated.An analysis model of contact melting inside a cylinder tube with constant heat flux was established.Control equations of melting were established with Nusselt's liquid film theory,and dimensionless melting equations were obtained theoretically.Melting velocity,thickness and pressure distribution of molten layer were discussed,and they were compared with melting under Dirichlet condition to study melting law with Neumann condition.It was found that molten film thickness increases as height of solid decreases,and melting velocity decreases during melting process.Heat flux has great effect on melting while heat flux is low.

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Numerical Simulation of Magnetohydrodynamic Flow in Duct with Flow Channel Insert MAO Jie, PAN Huachen, NIE Xin 2011, 28(4): 535-539.  Abstract ( )   PDF (272KB) ( )   Mangetohydrodynamic flow in a rectangular duct with flow channel insert and pressure equalization slot for fusion liquid metal blanket is studied numerically with a two-dimensional fully developed flow model.Velocity field and MHD pressure drop varying with Hartmann number and electric conductivity of FCI is analyzed.Compared with normal duct flow,MHD pressure drop with insulating FCI is reduced significantly.Dimensionless MHD pressure drop decreases as Hartmann number grows.Furthermore,reduction of MHD pressure drop becomes weaker as FCI electric conductivity increases.Reverse flow at pressure slot is related to electric conductivity of FCI.Numerical results are in good agreement with experimental and simplified results.

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Size Effect in Void Growth and Coalescence of Face-centered Cubic Copper Crystals PANG Weiwei, ZHANG Guangcai, XU Aiguo, LU Guo 2011, 28(4): 540-546.  Abstract ( )   PDF (969KB) ( )   Dynamics of a pair of voids located along loading direction under uniaxial tension is investigated using molecular dynamics method.Size effects in void growth and coalescence are studied.It shows that different-sized voids grow and coalesce through dislocation nucleating on void surfaces.In early elastic stage,voids grow along loading direction,then along vertical direction and finally form octahedral-like structures in plastic stage.Critical yield stress increases with decreasing of void size.If radius is large,dislocations nucleate and migrate symmetrically.Voids elongate in loading direction,and evolution process is similar.If radius is small,dislocations nucleate asymmetrically and voids elongate along vertical direction.The process of void growth may be characterized by elastic deformation,independent growth,coalescence and steady growth.Independent growth stage diminishes gradually as void size becomes smaller.

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Grid Movement Algorithms in CFD for Numerical Simulation of Bridge Vibration SUO Qifeng, WU Qing, ZHONG Yicheng, LI Mingshui 2011, 28(4): 547-553.  Abstract ( )   PDF (1102KB) ( )   Delaunay background grid,edge spring grid and linear spring grid are used to study computational domain grid movement on non-structural grid and structure grid for non-streamlined bridge section.It shows that the methods are effective as grid deformation within a normal vibration amplitude of the bridge section.Delaunay grid background method consumes the least time and the linear spring grid method obtains the highest quality.It also shows that with large amplitudes,structural grid is invalid easily and linear spring grid method ensures effectively.

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Extrapolative Method in Pattern Calculation and Synthesis of Large Plane Arrays ZHANG Shuai, GONG Shuxi, GUAN Ying, GONG Qi 2011, 28(4): 554-560.  Abstract ( )   PDF (409KB) ( )   An efficient method is shown for radiation pattern of large plane arrays.Active element patterns of a large plane array are constructed from those of a small linear array.Field radiated by a large plane array is obtained by summing up active element pattern of all elements.With this method a large plane array analysis problem is converted into a small linear array problem,and thereby computational cost is considerably reduced.In addition,a hybrid method using extrapolative method combining with genetic algorithm is proposed for synthesizing desired patterns of large plane arrays.To assess accuracy and efficiency of the hybrid method,a low side lobe 10×10 plane microstrip patch antenna array is synthesized with the method.Calculated results agree well with that by HFSS.

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FDTD Combined with DFT for Analysis of BroadbandHigh-power Microwave Propagation in Air ZHAO Pengcheng, ZHOU Haijing, TANG Tao, LIN Wenbin, LIAO Cheng 2011, 28(4): 561-568.  Abstract ( )   PDF (400KB) ( )   With Maxwell equations and electron fluid equations Gaussian,damped sinusoidal broadband high-power microwave(HPM) propagation in air is analyzed by using finite difference time domain(FDTD) method.At each time grid,according to electronic velocity of narrow-band pulse,effective electric field of broadband pulse is solved with discrete Fourier transform(DFT) method.Ionization parameters at each spatial grid are updated by substituting effective electric field and pressure into corresponding formulas.Calculation accuracy is improved.It shows that broadband HPM pulse amplitude,pulse width,height above sea level have significant effect on air breakdown.Tail loss is resulted from air breakdown.As propagation distance increases,HPM pulse tail decay increases and spectrum of pulse is broadened,splited,and center frequency shifts.

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Atmospheric Diffusion Loss of Radiation Belt Trapped Electrons Injected by High Altitude Nuclear Detonation NIU Shengli, LUO Xudong, WANG Jianguo, QIAO Dengjiang 2011, 28(4): 569-575.  Abstract ( )   PDF (294KB) ( )   With Fokker-Plank equation of pitch-angle diffusion,a numerical method for atmospheric diffusion loss of radiation belt trapped electrons is shown.Flux and energy spectrum are calculated as atmospheric scattering of fission β spectrum electrons injected in radiation belt by high altitude nuclear detonation.Diffusion due to atmospheric scattering is remarkable as L < 1.3.Low energy electrons are removed more rapidly than those with high energy.Electron flux decays rapidly at an initial phase and then decays gradually as an exponential function of time.

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Structure and Potential Energy Function of Ground State of NFX(X=-1,0,+1) XIAO Xiajie, JIANG Lijuan, LIU Yufang 2011, 28(4): 576-582.  Abstract ( )   PDF (334KB) ( )   Density functional theory B3LYP method is used to optimize ground-state structures of NF molecule,NF+ and NF- molecule ions with 6-311+ +g(df,3pd),6-311g(3d,3p) and 6-311+ +g(3df,3pd) basis sets,respectively.Frequency and single-point energy scan for NFX(X=-1,0,+1) are calculated.With the least-square method,spectral parameters (Be,αe,ωe,ωeχe) of NF molecule and NF+ ion ground state are fitting to Murrell-Sorbie functions.Calculated results are in good agreement with experiments.Spectral parameters (Be,αe,ωe,ωeχe) and force constants (f2,f3,f4) of NF- molecular ion ground state are shown.

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RCEP Modulation on Evolution of Two-color Femtosecond Pulses and Spectrum in a Dense V-type Medium LIANG Bian, JIA Kening, LIANG Ying, TONG Dianmin, FAN Xijun 2011, 28(4): 583-588.  Abstract ( )   PDF (335KB) ( )   In one-photon resonance and detuning cases,effect of relative carrier-envelope phase(RCEP) on evolution of two-color sech-type femtosecond pulses and spectrum in a dense V-type three-level atomic medium is investigated with full Maxwell-Bloch equations.Modulation of RCEP on pulse shape and spectral property of two-color pulses in detuning case is more evident than that in single-photon resonance case.And in detuning case we get spectrum broadening much greater than that in resonance case.Supercontinuum with the highest frequency of 18 times of incident frequency appears.

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Theoretical and Numerical Studies on Stimulated Raman Scattering by a Chirped Laser Pulse XU Feng, CAO Lihua 2011, 28(4): 589-597.  Abstract ( )   PDF (410KB) ( )   We analyze effect of a small-bandwidth linear frequency chirp on growth of Raman instability with coupled relativistic Maxwell-fluid equations.It is shown that threshold of Raman backward scattering is increased by frequency chirp with no dependence on the sign of chirp.And growth rate of Raman forward scattering increases(decreases) for a positive(negative) chirp.In addition 1D3V particle-in-cell simulations are performed.It shows agreement with theoretical analysis.

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Structure and Electronic Properties of WnC0,±(n=1,…,6) Clusters ZHANG Xiurong, KANG Zhangli, LI Yang 2011, 28(4): 598-604.  Abstract ( )   PDF (742KB) ( )   Possible equilibrium geometries of WnC0,±(n=1,…,6) clusters are optimized with density functional theory at B3LYP/LANL2DZ level.Stability and electronic properties of ground state structures are analyzed.It shows that as n > 3 cluster undergoes a transition from a two-dimensional structure to a three-dimensional structure,and carbon atom remains on the surface of cluster.Stability of Wn cluster is increased with doped carbon atom.Moreover W3C is the most stable one among WnC0,±(n=1,…,6) clusters,and it is taken as a basic structure.Electronic properties of WnC0,±(n=1,…,6) clusters are characterized by analyzing energy gaps,vertical electron affinities(VEA) and vertical ionization potentials(VIP) of WnC with pure Wnclusters.WnC clusters get electron easily and shows higher nonmetallicity than Wn clusters.

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Electronic Transport Properties of Alkanemonothiol Molecular Membranes:Molecular Interactions LI Yingde, LI Zongliang, WANG Chuankui 2011, 28(4): 605-610.  Abstract ( )   PDF (887KB) ( )   With density functional theory(DFT) and elastic scattering Green's function method,electronic transport of alkanemonothiol molecular membranes were simulated theoretically.It shows that conductive ability of molecular membranes increased 2 to 3 orders of magnitude than that of a single molecule due to interaction between molecules.Conductive ability of a molecular junction increases with increasing external force.Increase of current is mainly due to increased probability of tunneling within and between chains in a molecular junction.The increased probability is caused by coupling enhancement between molecule and electrode and between molecules.

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Computation of Distinguished Trajectories in Time Dependent Vector Fields SUN Hengyi, FAN Yangyu, JIA Meng, LI Huimin, ZHANG Jing 2011, 28(4): 611-620.  Abstract ( )   PDF (389KB) ( )   With definition of DHT(distinguished hyperbolic trajectory) and existing measure function in phase space,a measure function in extended phase space is presented.Existing algorithms with constant accuracy parameters is laborious as high precision is required.In order to overcome this shortage,a variable-step convergence algorithm is proposed.The main idea is to estimate initial region with the help of ISP(instantaneous stagnation points) and adopt variable-step grids to increase efficiency.With theoretical analysis and numerical calculation,an optimal range of key parameter is given.Two-dimensional and three-dimensional Duffing systems are used to test the performance.It shows that convergence route gained by the developed measure function is smooth and stable.And the variable-step convergence algorithm is more efficient.

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Computation of Two-dimensional Invariant Manifolds with Radial Growth Factor SUN Hengyi, FAN Yangyu, LI Huimin, ZHANG Jing, JIA Meng 2011, 28(4): 621-625.  Abstract ( )   PDF (669KB) ( )   In order to balance growth rate of manifold in all directions and construct global manifold structure of a dynamical system,a radial control factor is adopted to normalize the original dynamical system.Taking radius component of the tangent vector as a standard,this method controls manifold expanding at same speed in all directions.Theoretical analysis and example calculation demonstrate that manifolds before and after normalization have same orbit with the original one,which means their global manifold structures are consistent.Lorenz and Duffing systems are taken for examples to demonstrate effectiveness of the proposed approach.It indicates that the method not only get same effect as geodesic process but also present manifold in discrete flow way,which avoids many complicated boundary value problems.

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Numerical Study on Depolarization in Dynamics of Spiral Waves in Excitable Media LI Guangzhao, TANG Guoning 2011, 28(4): 626-632.  Abstract ( )   PDF (1052KB) ( )   Since refractory states of an excitable medium can be excited,depolarization is introduced into the Bar model.Depolarization effects on spiral waves are investigated.It shows that as threshold of depolarization and depolarization duration are chosen suitably,depolarization can induce drifting and meandering of spiral wave and even cause spiral wave moving out of boundary of the system.The dense spiral wave,two-arm spiral wave,twin speaks wave,multiple spiral wave and spatiotemporal chaos can also be generated with depolarization.Physical mechanism underlying these phenomena is discussed.