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25 November 2000, Volume 17 Issue 6 Previous Issue    Next Issue

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THE COUPLED METHOD BASED ON THE NATURAL BOUNDARY REDUCTION FOR PARABOLIC EQUATION DU Qi-kui, YU De-hao 2000, 17(6): 593-601.  Abstract ( )   PDF (249KB) ( )   A natural boundary reduction initiated and developed by Feng Kang and Yu Dehao[1~4] is applied to solve the exterior initial boundary value problem of 2D parabolic equation, and a new coupled method of the natural boundary element method(NBEM) and finite element method(FEM) is suggested. The governing equation is first discretized in time, leading to a time-stepping scheme. Second, the natural integral equation over circular domain is given, and the coupling of the NBEM and FEM for the parabolic equation with unbounded domain is studied. Finally, a numerical example is devoted to illustrate this new method.

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A DISCRETE REGULARIZATION METHOD FOR THE NUMERICAL INVERSION OF ABEL TRANSFORM XIAO TING-yan, SONG Jin-lai 2000, 17(6): 602-610.  Abstract ( )   PDF (240KB) ( )   Based on Tikhonov's Regularization theory and the theoretical formula of the Abel inversion, a discreted regularization algorithm is proposed for the numerical inversion of Abel transform by integrating the regularized treatment on numerical diffrentiation with the weighted Gauss-type integral. The numerical test and the comparision study are made and show that the algorithm possesses the advantages of high accuracy, good numerical stability and practicability.

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A TAYLOR-GALERKIN FINITE ELEMENT METHOD FOR HYPERBOLIC CONSERVATION LAWS YU Xi-jun, FU Hong-yuan 2000, 17(6): 611-618.  Abstract ( )   PDF (212KB) ( )   A scheme is hroposed for solving hyperboilc conservation laws by the Taylor-Galerkin finite element method. The scheme is obtained by discretizing hyperbolic conservation laws related to the Hamilton-Jacobi's equations. The scheme satisfies the TVD properties under the isometry meshes by modifying the numerical flux, whose idea is from the difference scheme construction. Numerical examples are given.

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ELECTROMAGNETIC SCATTERING FROM ELECTRIC-LARGESIZE ANTENNA-RADOME SYSTEMS WAN Guo-bin, WAN Wei, SHEN Zhe, ZHOU Qi-zhong 2000, 17(6): 619-624.  Abstract ( )   PDF (186KB) ( )   It uses the physical optics method(PO) to analyze the electronmagnetic scattering from electric-large size antenna-radome systems. Under assumptions of locally planar radome surface and locally plane wave characteristic of waves scatter from antennas, formulations of equivalent electric and magnetic currents on radome surface and the induced current on antenna surface are presented. Both monostatic and bistatic radar cross section(RCS) of a aperture anternna, a multilayered radome and the antenna radome system are calculated. Frequency response of the monostatic RCS and the effect of antenna inclination on RCS are also discussed. Numerical examples show efficiency of the PO method and significant effects of radomes on the scattering of antennas.

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PARALLEL LAGRANGE NUMERICAL SIMULATIONS FOR 2-DIMENSION THREE TEMPERATURE HYDRODYNAMICS MO Ze-yao, FU Shang-wu, SHEN Long-jun 2000, 17(6): 625-632.  Abstract ( )   PDF (191KB) ( )   By the design of new parallel algorithm and the organization of grid mapping, a serial code Lared-Ⅰ has been successfully parallelized for numerical simulations of 2-dimension three temperature hydrodynamics with the message passing programming environment. Moreover, a dynamic load balance method is also designed according to the physical and the code executing characteristics, which can significantly improve the parallel performance. The numerical results under both parallel computing environments are given as well.

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A SECOND-ORDER MOMENT TWO-PHASE TURBULENCE MODEL BASED ON THE LAGRANGIAN PDF XU Yi, ZHOU Li-xing 2000, 17(6): 633-640.  Abstract ( )   PDF (202KB) ( )   Using the Lagrangian analysis of particle motion and PDF(Probability Density Distribution Function) method,an improved the second-order-moment model of particle-phase is proposed.Based on the Lagrangian stochastic two-phase motion equations, using the stochastic-process analysis and the signal-system analysis, the obtained particle-phase PDF transport equation,the two-fluid model equations and the basic version of two-phase fluctuation velocity correlation are in agreement with those obtained by other investigators.However,significant improvement is made for the closure model.The crossing-trajectory effect,continuity effect,inertia effect and the anisotropic turbulence have been taken into account to simulate the interaction time between the particle and the fluid turbulence seen by the particles.

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TRAPPING OF HYPERTHERMAL PARTICLES: A MOLECULAR DYNAMICS SIMULATION DUAN Xiang-mei, GONG Xin-gao 2000, 17(6): 641-644.  Abstract ( )   PDF (96KB) ( )   It studies the trapping process of hyperthermal particles impacted on metal substrate by molecular dynamics simulations.Results show that,for normal incidence,the trapping probability decreases with increasing of the incident energy,while for 45° incidence,the trapping probability displays a non-monotonic behavior as observed in the recent experiment.The dependence of the trapping probability on the incident angle has also been investigated.

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MONTE CARLO STUDY OF ONE END ABSORBED POLYMER CHAIN WANG Zhi-hu, LUO Meng-bo 2000, 17(6): 645-648.  Abstract ( )   PDF (122KB) ( )   Polymer chain with one end absorbed to an infinitely large impenetrable wall on the simple cubic lattice is studied with Monte Carlo method.The mean square end-to-end distance <R2> and the mean distance of mass center <Z> from the wall are calculated.Results show that both <R2> and <Z> obey the scaling law, <R2>=αNγ,<Z>=βNη, where N is chain length,while γ,η,α, and β are functions of the parameter u(u=e-ε/kT,here ε is interaction energy between any pair of framework atom of the chain, k is the Boltzmann constant and T is the absolute temperature).It is found that γ increases from 1.01 to 1.19,and η increases from 0.51 to 0.60 when u decreases from 1 to 0.5.

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CALCULATION OF TRANSMISSION COEFFICIENTS FOR ONE-DIMENSIONAL POTENTIAL WITH ARBITRARY SHAPE AND STUDY OF RESONANCE TUNNELING PHENOMENA JING Xiao-gong, ZHAO Yong-fang, LU Tian-quan, ZHENG Yi-song, Li Tie-jin 2000, 17(6): 649-654.  Abstract ( )   PDF (147KB) ( )   The transmission coefficient for one-dimensional potential with arbitrary shape is calculated using the recurrence formulae of one-dimensional multi-stepped potentials. Resonance tunneling phenomena are studied with the curves of transmission coefficients varying with the energy of incident particles. In particular, the resonance tunneling phenomena in the semiconductor material GaAlAs/GaAs/GaAlAs are discussed in detail. The calculated results show that the resonance tunneling phenomenon for the potential, which has an arbitrary shape well between double symmetric square barriers could also exist.

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CHARACTERISTIC IMPEDANCE OF COUPLED OFFSET CYLINDRICAL BARS TRANSMISSION LINE BETWEEN PARALLEL PLATES ZHENG Qin-hong, QIAN Shuang-ping, XIE Fu-yao, MA Li, JIANG Shao-quan 2000, 17(6): 655-658.  Abstract ( )   PDF (120KB) ( )   A new approach,conformal transformation combined with the boundary element method(BEM),is presented for computation of the characteristic impedance of coupled offset cylindrical bars transmission line between parallel plates.By this new method,the numerical results are obtained from three fundamental offset structures.These impedance data not only permit the exact design of various offset configurations of slab lines,but also provide a known accuracy for manufacturing various coaxial configurations of slab lines.

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THE ELECTROMAGNETIC FIELD ANALYSIS OF LEVITATION MELTING WITH COLD CRUCIBLE DENG Kang, REN Zhong-ming, CHEN Jian-qiang, JIANG Guo-chang 2000, 17(6): 659-663.  Abstract ( )   PDF (139KB) ( )   By using the quasi-3D coupled current method presented, the influences of structure of cold crucible, power frequency, electricity property of charge(melt), coil(inductor)position and current on the electromagnetic field(EMF) and the levitation characteristics in the melting processes are analyzed. It is shown that in the melting process, power frequency and crucible structure are the decisive factors for the ability of penetrating magnetic flux into cold crucible. The magnetic flux density in cold crucible is reduced with the rising of power frequency, and this tendency becomes stronger when that is higher than 100 kHz. The segmented structure of cold crucible can reduce the induction eddy in itself effectively, and the higher the power frequency is, the better the result is. So, a cold crucible can be segmented into(16~20) sectors for higher frequency electromagnetic field(f>100 kHz),(8~12) sectors for high frequency one(10 kHz≤f≤100kHz), and(4~8) sectors for mid-high frequency one(f<10 kHz). It is also shown that the levitation force in melting charge is related to coil current as a parabolic function.

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SELF-MEMORY INTEGRATION SCHEME OF CONVECTION-DIFFUSION EQUATION LU Jun-an, Lü Jin-hu, XIA Jun 2000, 17(6): 664-670.  Abstract ( )   PDF (160KB) ( )   One parameter self-memory retrospective time integration scheme of convection-diffusion equation is derived. On the basis of the self-memory dynamics, the stability is discussed by using difference theory. The numerical examples show that this scheme has high accuracy and good stability.

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INFINITE STRIPEDLY DISTRIBUTED TRANSFER FUNCTION METHOD FOR OPTICAL WAVEGUIDES LI Hai-yang, FENG Ying, ZHOU Jian-ping 2000, 17(6): 671-677.  Abstract ( )   PDF (191KB) ( )   A stripedly distributed transfer function method with infinite elements is introduced, which is used to analyze the guided waves in optical channel waveguides. Two kinds of infinite elements are provided conesponding to analytic direction and discrete direction. In order to simplify the expression of the infinite elements, second order equations of transfer function is chosen with account taken of the character of Helmholtz equation. Numerical results are presented for rectangular waveguides and compaied with those of other methods. The results show the advantage of this method.

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STUDY ON THE APPLICATION OF GLOBAL OPTIMIZATION AL GORITHMS-GENETIC ALGORITHMS IN LEED STRUCTURE DETER MINATION HE Jiang-ping, TANG Jing-chang 2000, 17(6): 678-684.  Abstract ( )   PDF (180KB) ( )   The genetic algorithms(GAs) is applied for the low electron energy diffraction(LEED) calculation. A computer program GAs-LEED has been developed to perform the automatic search of surface structure. It is found that the GAs-LEED analysis of Pt(111)-p(2×2)0 shows a global minimum in the parameter space.

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COMP ARISON OF 2-D COMPUTATION ALSI MUL ATION ON PELLET IMPLOSION LI Yun-sheng, HUANG Shu-ke, FU Shang-wu 2000, 17(6): 685-689.  Abstract ( )   PDF (152KB) ( )   The compressed shapes of the pellet driven by a radiation field in a cylindrical gold hohlraum under single ring driving of incident laser beams simulated by RT3D and Lared-Ⅰ codes are given. As the position of the incident laser spots changing, the temperature distribution on the pellet surface changes as well and the pellet shapes turned out to be cake-like, sausage-like or ball-like respectively according to the different position of the laser spots. The comparison of the simulation result with the experiment carried out in LLNL and with the simulation result by Lasnex codes is given here too and it is shown that the same conclusion and the similar numerical result was obtained. Meanwhile it can also be seen that under single ring driving, it is not enough to supply a uniform and symmetrical radiation fields and it would be necessary to develop two or three laser rings driving to improve the radiation field.

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NUMERICAL SIMULATION OF FLOW FLUID AND HEAT TRANSFER IN THE MOULD OF CONTINUE CASTING GONG Tao, YANG Hai-xi, DENG Kang 2000, 17(6): 690-694.  Abstract ( )   PDF (161KB) ( )   A two dimension turbulence model is presented to simulate the fluid flow and heat transfer in casting mould, and Ansys software applies to solve the equations. By means of simulating the flow fields and temperature fields of different inlet velocities, the relations betwen the inlet velocity and the quality of ingots are analyzed. Finally, the comparison between the predicted results and the measured data in BAO Steel is given,and shows that both are in good agreement.

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NUMERICAL SIMULATION OF UNSTEADY FLOW WITHIN CYLINDRICAL CONTAINER ZHONG Fang-ping 2000, 17(6): 695-701.  Abstract ( )   PDF (264KB) ( )   The axial transient flow within a cylindrical container is simulated numerically using a NND finite difference scheme. The self-similar solution of the point-source explosion problem is obtained to give initial conditions. Shock loads at the inner wall of the vessel and the development of the flow field are deterimined through this numerical simulation. Results are discussed and compared with experimental data in other literatures.

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MATERIAL PARAMETER IDENTIFICATION OF THE CONCRETE GRAVITY DAM WITH REGULARIZING LEAST SQUARES METHOD LI Shou-ju, LIU Ying-xi, WANG Deng-gang, CHEN Chang-lin, LI Zheng-guo 2000, 17(6): 702-706.  Abstract ( )   PDF (123KB) ( )   Based upon the horizontal displacements data in-situ in the top of concrete gravity dam, the parameter identification problem is done with the regularizing least squares method for the elastic modulus of the concrete gravite dam. The iterative format and selecting algorithm of the regularizing parameters are set up. It is also put forward to identify material physical properties according to the priori information. The practical use of the parameter identification algorithm proposed shows that this algorithm has fast convergence speed and good stability.

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SYMMETRIC TAYLOR VORTEX FLOW BETWEEN TWO CONCENTRIC ROTATING SPHERES MEI Li-quan, WANG Li-zhou 2000, 17(6): 707-711.  Abstract ( )   PDF (223KB) ( )   A finite element method is used to numerically study the steady axisymmetric incompressible flow between two concentric rotating spheres. The non-uniqueness of the supercritical flow exhibits three different modes with zero,one and two Taylor vortices at each hemisphere.

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THE ANTENNA DESIGN OF FAST WAVE HEATING ZHU Xue-guang, KUANG Guang-li, ZHAO Yan-ping, LI You-yi, XIE Ji-kang 2000, 17(6): 712-718.  Abstract ( )   PDF (174KB) ( )   The coupling efficiency of antenna in tokamak for ion cyclotron resonance heating frequency range, depends mainly on the system and size of the antenna. Based on the difference of plasma absorption performance to different spectrum component,and on whether the antenna current spectrum matches the spectrum of plasma absorption, the problem of antenna design of fast wave heating is discussed in detail.