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25 November 2001, Volume 18 Issue 6 Previous Issue    Next Issue

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RAY TRACING、 SYMPLECTIC ALGORITHMS AND WAVE FIELD SIMULATION CHEN Jing-bo, QIN Meng-zhao 2001, 18(6): 481-486.  Abstract ( )   PDF (221KB) ( )   The relationship between ray tracing、symplectic algorithm and wave field simulation is presented. The long time conservation property of symplectic algorithm and the necessity of ray tracing using symplectic algorithm are demonstrated. In addition, wave field simulation using Maslov asymptotic theory and symplectic algorithm for linear layer model is performed. The comparison of the numerical solution with the analytic solution is carried out.

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WRONSKIAN-PRESERVING ALGORITHM OF MODEL IN THE STRONG LASER FIELD LIU Xue-shen, LIU Xiao-yan, YANG Yu-jun, DING Pei-zhu, ZHU Qi-ren 2001, 18(6): 487-490.  Abstract ( )   PDF (164KB) ( )   The symplectic algorithm in the complex symplectic space is the algorithm that preserves the Wronskian.The Wronskian calculated by using the symplectic scheme keeps unchanged which is in good agreement with theoretical analyses after a long distance of computation.The numerical solutions of the one dimensional model of strong laser field are calculated by using the Wronskian preserving and symplectic scheme.

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THE TIME-SAVING NUMERICAL METHOD FOR GPS/MET OBSERVATION OPERATOR AND ITS PARALLEL COMPUTING LI Shu-yong, WANG Bin 2001, 18(6): 491-496.  Abstract ( )   PDF (274KB) ( )   The Global Positioning System (GPS) ray-shooting method is a self-sufficient observation operator in GPS/MET (Meteorology) data variational assimilation.The huge computation of the GPS ray-shooting method,however,makes it impossible so far to be applied in data assimilation and operational prediction.In order to reduce the huge computation,a 2nd-order timesaving symplectic scheme is used to solve the equations of the GPS ray trajectory due to its separable Hamiltonian nature.Not only does it save 75% of the CPU time the old GPS ray-shooting model using 4th order Runge Kutta method takes,but also does the simulation accuracy be improved slightly to some extent.Then the parallel computing of the new GPS ray shooting model is studied.The speed up and the parallel efficiency are both very high.

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A CHARGE CONSERVATION STATISTICS ENHANCEMENT METHOD USED IN SEMICONDUCTOR DEVICE MONTE CARLO SIMULATION DU Gang, LIU Xiao-yan, SUN Lei, HAN Ru-qi 2001, 18(6): 497-500.  Abstract ( )   PDF (157KB) ( )   A charge conservation statistics enhancement method used in semiconductor divice Monte Carlo simulation is approached,which smoothes the charge fluctuation caused by the statistics enhancement, and keeps the continuation of cross edge charge flow. As an example, Schottky barrier diode characteristics is simulated using this method.

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NUMERICAL STUDY OF GUASSIAN SPHERICAL WAVE MODIFIED METHOD OF THE PARAXIAL WAVE EQUATIONS IN THE UNSTABLE CAVITY FU Han-qing, WANG Tai-chun 2001, 18(6): 501-506.  Abstract ( )   PDF (242KB) ( )   The advantages and disadvantages of the 3D paraxial wave equations in the confocal unstable cavity solved by the difference methods and 3D Fresnel integral equations solved by the numerical integral method and the fast Fourier transform (FFT) method are analyzed. It is assumed that the laser beam in the unstable cavity transfers by the modified Guassian spherical wave. By using a coordinate transformation, the diverging or converging beam is converted into equivalent collimated beam. The paraxial wave equation of the modified function is solved by FFT method. Under the same conditions, the obtained results coincide with those in the internal and external references. The near field and far field results computed in confocal unstable cavity of the COIL experiment are reasonable.

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DSMC FOR GAS FLOWS IN A MICROCHANNEL QIN Feng-hua, SUN De-jun, YIN Xie-yuan 2001, 18(6): 507-510.  Abstract ( )   PDF (161KB) ( )   Gas flows driven by pressure in a microchannel are computed with the direct simulation Monte Carlo (DSMC) method. The rarefied effect is observed and slip velocity exists at solid boundaries. Temperature is almost constant in the whole flow field. The Mach number of the flow is very low. Density and pressure vary significantly along the channel while they are nearly invariant transversely. Nonlinearity of pressure distribution along the channel due to compressibility is found and reduces as the Knudsen number increases.

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CALCULATION OF 1-D COMPRESSIBLE TWO-COMPONENT FLOWS BY A COUPLED LEVEL SET METHOD WITH GHOST FLUID CORRECTION ZHANG Lei, YUAN Li 2001, 18(6): 511-516.  Abstract ( )   PDF (205KB) ( )   1-D compressible two component flows are computed with a modified Level Set method where the Euler equations and Level Set equation are combined into a whole conservation law and are solved with high resolution finite difference schemes. In order to minimize the numerical oscillation near the fluid interface, the Ghost Fluid method is used together with the Isobaric Fix, and numerical results are presented for 1-D problems.

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PIECEWISE PARABOLIC METHOD FOR COMPRESSIBLE FLOWS OF MULTIFLUIDS WITH HIGH DENSITY RATIOS MA Dong-jun, SUN De-jun, YIN Xie-yuan 2001, 18(6): 517-522.  Abstract ( )   PDF (215KB) ( )   A high order Piecewise Parabolic Method (PPM) is applied to simulate compressible multifluids flows with a stiffened gas equation of state in multi dimensions, which allows high density ratios and strong shock waves. Several test problems are presented for one and two dimensions.

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NUMERICAL MODELING OF POOL FIRES WANG Jian, CHEN Xian-fu, DOBASHI Ristu, FAN Wei-cheng 2001, 18(6): 523-526.  Abstract ( )   PDF (138KB) ( )   The numerical computation is often used to predict or study pool fires.The fluid flow,heat and mass transfer,chemical reaction and their interaction in the burning process are studied by formulating and solving a set of governing equations.The treatment of oil surface is given in details also.Many results of pool fires under various wind speeds are gained,and computational results are obtained.

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THE INSTABILITY ANALYSIS OF ION TEMPERATURE GRADIENT DRIVEN IN A TOKAMAK PLASMA WITH NEGATIVE MAGNETIC SHEAR JIAN Guang-de, HUANG Lin 2001, 18(6): 527-530.  Abstract ( )   PDF (167KB) ( )   An eigenmode equation of ion temperature gradient driven instability in a tokamak plasma with negative magnetic shear is solved numerically by the shooting method.Numerical calculations show that the toroidal rotation sheared flow can modify the sheared slab ηi instability and has a stabilizing ηi role in the plasma core near minimum q magnetic surface.

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EXISTENCE,UNIQUENESS AND STABILITY OF INVERSE NEUMANN BOUNDARY VALUE PROBLEM OF POISSON EQUATION CHEN Qi, MA Yi-chen, YING Gen-jun, YANG Xiao-bin 2001, 18(6): 531-538.  Abstract ( )   PDF (285KB) ( )   Results of existence,uniqueness and stability recovering the domain from a measured data of Poisson equation are obtained.The results of determining the shape of unknown domain are proven with Sobolev theory and the fundamental solution of Poisson equation.

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PARALLEL COMPUTATION OF FLUID INTERFACE INSTABILITY IN THREE DIMENTION WITH RANDOM PERTURBATION TANG Wei-jun, ZHAO Ning, LI Xiao-lin, ZHANG Jing-lin, YU Xi-jun 2001, 18(6): 539-543.  Abstract ( )   PDF (222KB) ( )   Computation of three dimensional fluid interface instability with random perturbation is performed on a 8 CPU personal parallel computer system.The parallel computation platform is a message passage interface (MPI).A second order TVD scheme with Ghost method is applied with a fully parallel algorithm to the 3D Euler equations.Level Set function is used to track the motion of a fluid interface in an Eulerian framework.Buffer zone and data communication are discussed.The number of computation meshes is about 1 million.Bubble evolution with random perturbation in Rayleigh Taylor instability is obtained by numerical simulation.

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THE MATHEMATICAL MODEL OF WELDPOOL SURFACE SHAPE AND DISTRIBUTION OF DROPLET HEAT CONTENT IN MIG WELDING SUN Jun-sheng, WU Chuan-song 2001, 18(6): 544-548.  Abstract ( )   PDF (185KB) ( )   By considering the interactional physical process of droplet and weldpool, a mathematical model of weldpool surface deformation and a distribution model of droplet heat content inside weldpool are established. Numerical simulation technique is employed to analyze the correlation of welding parameters, distribution volume of droplet heat content and welding seam figuration. The experiments show that the simulation results are in agreement with the measured ones.

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DISCONTINUOUS FINITE ELEMENT METHODS FOR HAMILTON-JACOBI EQUATIONS LI Xiang-gui, YU Xi-jun, CHEN Guang-nan 2001, 18(6): 549-555.  Abstract ( )   PDF (270KB) ( )   Two numerical schemes of discontinuous finite element methods are presented for Hamilton Jacobi equations which are obtained by using the different basic functions. The numerical solutions of these schemes converge to weak solutions of the Hamilton Jacobi equation under some conditions. Numerical tests given illustrate the accuracy and resolution of discontinuity for the two different schemes.

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NUMERICAL METHOD AND SIMULATION OF SEAWATER INTRUSION AND PROTECTION PROJECTS YUAN Yi-rang, LIANG Dong, RUI Hong-xing 2001, 18(6): 556-562.  Abstract ( )   PDF (250KB) ( )   The simulation of the process and the effects of protection projects lays the foundation of its effective control and defence. A mathematical model of the problem and the upwind fractional step finite difference method are presented. Using this method, the numerical simulation of seawater intrusion in Laizhou Bay Area of Shandong Province is given. The numerical results turn out to be identical with the real measurements, so the prediction of the consequences of protection projects is reasonable.

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MIXED AND DISCONTINUOUS FINITE ELEMENT METHOD USED TO NEUTRON DIFFUSION EQUATION YANG Yin-ling, GUO Xiu-lan, MA Yi-chen, ZHANG Zhi-bin 2001, 18(6): 563-568.  Abstract ( )   PDF (169KB) ( )   A variational formula combining mixed finite element method with discontinuous finite element method is derived for solving the two group neutron diffusion equation in 2D. According to the variational formula, a numerical test is given whose result proves that the variational formula is reasonable and practicable. In order to improve the precision of the calculation, there are more to be studied.

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THE EFFECT OF BLADE-TIP SHAPE ON ROTOR AEROACOUSTIC NOISE BY EULER/KIRCHHOFF METHOD SONG Wen-ping, HAN Zhong-hua, WANG Li-qun, YANG Ai-ming, QIAO Zhi-de 2001, 18(6): 569-572.  Abstract ( )   PDF (156KB) ( )   The Euler/Kirchhoff method is adopted to calculate the far field noise of UH-1H rotor,and the calculated results are compared with the measured data.The effect of rotor blade tip shape on high speed rotor noise is investigated.The results show that,with the decreasing of airfoil thickness near the blade tip or the increasing of the taper ratio near the blade tip and the sweep of the blade tip, the high speed rotor noise can be reduced to some extent.

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THREE-DIMENSIONAL UNSTRUCTURED MESH GENERATION ZHU Pei-ye 2001, 18(6): 573-576.  Abstract ( )   PDF (207KB) ( )   An unstructured mesh generation method for three dimensional region is described. The boundary surfaces are triangulated by a two dimensional anisotropic triangulation method. Then the three dimensional meshes are generated by means of a constrained Delaunay algorithm with automatic field point creation. Methods for mesh quality optimization are also discussed. Several examples are given to show the applications of the method.