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25 November 2007, Volume 24 Issue 6 Previous Issue    Next Issue

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Difference Scheme for Diffusion Equation on Voronoi Meshes YU Huaping, WANG Shuanghu 2007, 24(6): 631-636.  Abstract ( )   PDF (237KB) ( )   A difference scheme for diffusion equation on Voronoi meshes is constructed using finite volume method.The diffusion discretization scheme is simpler on Voronoi meshes than on quadrilateral meshes.It introduce no cell-node unknown and improves accuracy of the discrete calculation of cell-edge flux as well as accuracy of difference scheme.The diffusion calculation on Voronoi meshes can be coupled with cell-centered hydrodynamics calculations.Computation examples demonstrate that the accuracy on Voronoi meshes is higher than that on quadrilateral meshes and Voronoi meshes adapt well to distortion.

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Numerical Methods Based on Characteristic Centered Finite Difference Procedure for a Class of Nonlinear Evolution Equations GUO Shuangbing, ZHANG Zhiyue 2007, 24(6): 637-646.  Abstract ( )   PDF (277KB) ( )   We propose a characteristic centered difference method for a class of nonlinear evolution equations on nonregular grids.Approximate solution and error estimate of u,ut,ux,utx are obtained.The compuational load of the method is the same as those of the characteristic difference method based on linear interpolation.And the error order of the approximate solution is the same as one of the characteristic difference method based on quadratic interpolation.Moreover,the first derivative of u,ut in space shows super-covergent order error estimate.Numerical results demonstrate feasibility and efficiency of the methods.

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A Grid Generation Strategy for Domains with Complicated Boundaries YAO Yanzhong, WANG Ruili, YUAN Guangwei 2007, 24(6): 647-654.  Abstract ( )   PDF (447KB) ( )   A structured grid generation method for domains with complicated boundary is discussed.Based on the Winslow method with variational form,and combined with grid untangling and area averaging technologies,a discrete functional is designed. The minimization of the discrete functional is solved by an optimization algorithm,and good grids are generated.Numerical experiments show that the method is robust and generates grids with good geometric qualities on complicated domains.This method inherits advantages of the Winslow method and overcomes some faults.

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Charge-conserving Current Assignment Algorithm in Particle Simulation of Plasma YIN Yan, CHANG Wenwei, XU Han, ZHUO Hongbin, MA Yanyun 2007, 24(6): 655-659.  Abstract ( )   PDF (250KB) ( )   A charge-conserving current assignment algorithm based on current conservation equation proposed by Villasenor and Buneman is introduced.It is found that the algorithm is not available as particle boundary conditions are adopted. With typical boundary conditions amendment methods are proposed in which the simulation satifies charge conservation.

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NND and Weighted NND Scheme with Power Limiter ZHAO Haiyang, LIU Wei, YANG Xiaoliang, REN Bing 2007, 24(6): 660-666.  Abstract ( )   PDF (283KB) ( )   To design a high-order accurate shock capturing method for hyperbolic conservation laws,we introduce a new power limiter to obtain a second-order power NND scheme and a third order power WNND scheme based on modification of NND scheme and WNND scheme.By applying the limiter to first-order differences of the candidate stencils,the power NND scheme and the power WNND scheme reduce the smearing near discontinuities.The power NND scheme and the power WNND scheme show less dissipation and less spurious oscillations,and catch the discontinuities more accurately than NND scheme and WNND scheme.The results of power NND scheme are similar to those of WNND scheme,and even better in some examples.The simulation of forced oscillation of the NACA0012 airfoil by power WNND scheme is in good agreement with experiments.

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Numerical Simulation on Evolution of Ablation Plasma Generated by Strong Laser TONG Huifeng, TANG Zhiping, ZHANG Ling 2007, 24(6): 667-672.  Abstract ( )   PDF (212KB) ( )   A general Godunov finite difference scheme—WENO(Weighted Essentially Non-Oscillatory) scheme with fifth-order accuracy is used to calculate 2-dimensional axis symmetrical laser-supported plasma flow field under laser ablated solid target,considering ionization degree of plasma and the interaction and coupling between laser beam and plasma.Evolution of the ablation plasma due to the interaction between laser and solid target is obtained.The simulation shows that the laser beam is strong absorbed by plasma on target surface,and the velocity of LSD(Laser Supported Detonation) wave is half of the ideal LSD derived with C-J detonation theory.

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Simulation of Static Power/Ground Networks with Improved Compressed Random Walk Algorithm SU Haohang, ZHANG Yimen, ZHANG Yuming, XIE Min, MAN Jincai 2007, 24(6): 673-676.  Abstract ( )   PDF (164KB) ( )   The static power and ground(P/G) network is analyzed by a combination of compressed equivalent circuit modeling and random wall algorithm.A model of power and ground network is obtained by parameter extraction and modeling over whole chips.The method builds an equivalent model for original network and uses random walk method to solve the simplified network.As a result,the improved compressed random walk algorithm saves CPU time greatly.The speed of the algorithm is more than two order of magnitude faster than the normal random walk algorithm.

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Synchronization of Chaotic Degenerate Optical Parametric Oscillator by Hyperchaotic Signal Modulating Parameter FENG Xiuqin, SHEN Ke 2007, 24(6): 677-682.  Abstract ( )   PDF (202KB) ( )   We study chaotic synchronization in degenerate optical parametric oscillators(DOPOs) by hyperchaotic signal modulating parameter.It shows that synchronization or inversed synchronization is realized in two or more chaotic systems by adjusting modulating coefficient as the maximum condition Lyapunov exponent(MCLE) of the system is negative.It is observed that the synchronization states depend on initial conditions and modulating coefficients.Under certain initial conditions,the synchronization state shows spontaneous mutation at some modulating coefficients.

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A Method Amplifying Output Power of MFCG YU Cuiying, DONG Zhiwei, WANG Yuzhi, WANG Guirong, YANG Xianjun, ZHAO Qiang 2007, 24(6): 683-687.  Abstract ( )   PDF (206KB) ( )   A method that decreases useless magnetism pressure to amplify the power of MFCG(magnetic flux compression generator) is proposed, in which the charging loop is cut off after initial current is provided.By code MFCG(V),the simulation demonstrates effectiveness of the method.

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A Finite Analytic Numerical Method in PDF Model for Two-phase Flows and Simulation of Wall Jet Loaded with Solid Particles XU Jiangrong, ZHOU Junhu, CEN Kefa 2007, 24(6): 688-692.  Abstract ( )   PDF (190KB) ( )   A method is presented to deal with high-dimensional scalar PDF(probability density function) transport equation for two-phase flow in phase space (X, V), in which the PDF transport equation is reduced to velocity phase space.The particle velocity PDF fv(V) is solved analytically and the particle position PDF is obtained statistically with Monte Carlo techniques. It shows that the method is better than the particle Reynolds stress trajectory model(PRST Model) in simulating a turbulent wall jet loaded with solid particles.

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Spin-orbital Energy Gap in One-dimensional Spin-orbital Model ZHU Rui 2007, 24(6): 693-697.  Abstract ( )   PDF (202KB) ( )   The spin-orbital energy gap in a one-dimensional spin-orbital model deduced from a degenerate Hubbard model with intrasite Hund rule coupling is studied.By using a mean-field method with SU(4) constraint fermion representation of spins and orbitals the valence bond order parameter,quasi-particle excitation gap and the spin and orbital density-density correlation functions are calculated.It is found that,as the Hund's coupling strength increases the excitation spectra show a gap and the magnetic configuration changes from a frustrating disordered state to a spin ferromagnetic and orbital antiferromagnetic ordered state at J1/J2=1/3.

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Convergence Acceleration of High-order Weighted Compact Nonlinear Scheme (WCNS) for Compressible Flows ZHANG Yifeng, DENG Xiaogang, MAO Meiliang, CHEN Jianqiang 2007, 24(6): 698-704.  Abstract ( )   PDF (319KB) ( )   With a high-order weighted compact nonlinear scheme(WCNS) for space discretization,several different implicit methods,including LU-SGS,Gauss-Seidel point-relaxation,line-relaxation and GMRES(generalized minimal residual),are compared in the simulation of hypersonic viscous flows.Both point and line relaxations with analytical Jacobian matrix converge faster than those of LU-SGS.GMRES obtains a faster convergence rate combined with line relaxation.

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Analysis of Rotor Wake Stability by Eigenvalue Method WANG Hai, XU Guohua 2007, 24(6): 705-710.  Abstract ( )   PDF (240KB) ( )   A linearized analytical method for stability analysis of the helicopter rotor wake is given.The wake vortex filaments are discretized into a number of straight-line vortex segments and perturbations of the vortex filaments are described by the end-position change of vortex segments.Self-induced and mutually-induced effects of the tip vortices as well as the interaction between rotor blade and tip vortex are considered.Taking UH-1H and AH1G model rotors as numerical examples,stability of the rotor wakes in both hover and forward flight is analyzed.It is shown that there is a positive eigenvalue in rotor wake motion and the wake is intrinsically unstable.Furthermore,a regular change of the maximum divergence rate with wave number is observed.The maximum wake divergence rate is smaller and the instability is weaker in forward flight compared with that in hovering flight.

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An Improved Subgrid-scale Characteristic Length QIU Jian, GU Zhaolin, WANG Zanshe 2007, 24(6): 711-716.  Abstract ( )   PDF (314KB) ( )   In the Sagaut mixed-scale model,an improved subgrid-scale(SGS) characteristic length,representing the scale of local energy-containing SGS motions,is proposed.Large-eddy simulations(LES) at temporal mixing layer and neutral atmospheric boundary layer indicate that by the improved SGS characteristic length,satisfactory spatial distribution of the SGS motions can be obtained and are closer to the results of direction numerical simulations(DNS).Compared with the basic model,the modified model with the improved SGS characteristic length produces more accurate mean quantities and turbulent statistics.The results demonstrate its valuable and wide application to LES.

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Boundary Element Analysis of Four-pole Parameters and Transmission Loss of Silencers with Flow WANG Xueren, JI Zhenlin 2007, 24(6): 717-724.  Abstract ( )   PDF (353KB) ( )   A substructure method and a dual reciprocity boundary element method(DRBEM) are applied to calculate four-pole parameters and transmission loss of ducts and silencers with complex flow.Basic principle and numerical procedure are introduced in detail.It is shown that the DRBEM is valid to compute four-pole parameters and transmission loss of ducts and silencers with subsonic complex flow with higher Mach number.The substructure method reduces numerical complexity of the DRBEM and improves accuracy and computation speed.

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Upwind Finite Volume Element Method for Unsaturated Water Flows ZHANG Zhijuan 2007, 24(6): 725-732.  Abstract ( )   PDF (243KB) ( )   An unsaturated soil water flow equation is studied.A conservative form for the flow equation is established by using upwind finite volume element method.The error estimate of a fully discrete upwind FVE solution with form of O(Δt+h) is obtained.Numerical simulations demonstrate efficiency of the scheme.

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One Body Density Matrix of Nucleus in the Shell Model HU Zehua, SUN Weili, TIAN Dongfeng, ZHANG Benai 2007, 24(6): 733-739.  Abstract ( )   PDF (240KB) ( )   A method calculating one body density matrix of nucleus in the mean field shell model is proposed.One body density matrixes of double closed nuclei 40Ca,90Zr are calculated. The nucleon density and momentum distributions are calculated and compared with those by the Hatree-Fock-Bogolubov theory,local Fermi gas model and those by experiments,respectively.

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Simulation of Hydrogen Storage in Boron Nitride Nanotube Arrays ZHANG Libo, CHENG Jinrong 2007, 24(6): 740-744.  Abstract ( )   PDF (225KB) ( )   By the grand canonical Monte Carlo method,physisorption of hydrogen storage in single-walled boron nitride nanotube arrays(SWBNNTA) at moderate pressure with normal temperature is studied.The influences of tube diameter,distance between tubes and pressure on hydrogen physisorption in SWBNNTA are investigated.It indicates that at normal temperature and moderate pressure the hydrogen storage capacity(mass percent) of SWBNNTA is obviously greater than that of single-walled carbon nanotube arrays,and exceeds the commercial standard presented by U.S.Department of Energy.Corresponding theoretical explanation is given.

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Approximation on Calculation of Spontaneous Emission of Semiconductor Planar Micro-cavities ZHAO Hongdong, SUN Mei, HAN Liying, TIAN Hongli, GUO Dongtai, LIU He 2007, 24(6): 745-748.  Abstract ( )   PDF (144KB) ( )   The spontaneous emission spectra of semiconductor planar micro-cavities are calculated by Taylor series with high order and new variable.An approximation of spontaneous emission with TE mode in a planar micro-cavity with half wavelength and high reflectivity is obtained. In the planar semiconductor micro-cavities,combined with Fermi-Dirac distribution functions of electrons and holes,the spontaneous emission spectra in a small angle and all directions calculated are agree well with those by numerical integral.The approximation can be used to the spontaneous emission spectra in QW(quantum well) planar micro-cavities.

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Non-S State Energy Spectrum in a Screen Coulomb Potential with Monte-Carlo Hamiltonian FANG Yizhong, LI Hai, LI Yongyao 2007, 24(6): 749-752.  Abstract ( )   PDF (143KB) ( )   We investigate non-s bound states in a screen Coulomb potential V(r)=-λ exp(-αr)/r,with different algorithms.The Schrödinger equation is solved using 4-step Runge-Kutta Method and Monte-Carlo approach.We analyzed errors of the MCH method.The energy spectrum and wave function in ground state and excited state agree well with those of 4-step Runge-Kutta method.

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Calculation of Exciton Ground State Energies in PbS Quantum Dots Using Properties of B-splines HUI Ping 2007, 24(6): 753-756.  Abstract ( )   PDF (167KB) ( )   The exciton wave function is built to calculate the exciton ground state evergy E_g in PbS quantum dots using special properties of B-splines.The quantum size effect of PbS quantum dots is investigated.Compared to other calculations,the E_g calculated shows better agreement with experimental results.The effects of effective mass and barrier height of potential on E_g are investigated.