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25 March 1996, Volume 13 Issue 1 Previous Issue    Next Issue

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APPLICATIONS OF THE ROUNDARY ELEMENT METHOD FOR CALCULATING ACOUSTIC PERFORMANCE OF DUCTS AND MUFFLERS Ji Zhenlin, Zhang Zhihua, Ma Qiang 1996, 13(1): 1-6.  Abstract ( )   PDF (379KB) ( )   The governing equation of three-dimensional sound propagation in an uniform duct with mean flow and linear temperataure gradient is derived,based on the foundamental equations of aerodynamics.By using the interation method,the sound propagation equation is expressed as the case which can be computed numerically with the boundary element method.The four-pole parametes of a muffler can be obtained using BEM,therefore the acoustic per.formance such as transmission loss can be predicted.The transmission loss of an expansion chamber has been calculated and compared with the result obtained by means of the one-dimensional theory.

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APPLICATIONS OF THE FINITE-ELEMENT METHOD IN NUMERICAL SIMULATION OF NEUTRON WELL-LOGGING Zhang Jintao, Wu Hongchun, Ma Yichen, Zhong Zenqian, Fang Yingdong, He Qingyuan 1996, 13(1): 7-13.  Abstract ( )   PDF (383KB) ( )   This paper deals mainly with applications of the finite-element method in numerical simulation of neutron well-logging.In the frame of multigroup P1 approximation the neutron transport equation is soluted by using finite-element method and the two-dimentional finite-element code FEMLOG is developed for the numerical simulation of neutron well-logging.The precision of numerical results of FEM-LOG is satisfactorily comparable to that of the international common code DOT4.2.However FEM-LOG is operated on the computer far faster than DOT4.2.

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NUMERICAL SIMULATION OF LASER ABLATION AND A CALCULATING METHOD FOR TRACING PHASE-BOUNDARY Tao Yingxue, Shen Longjun, Guan Jili, Liu Chenghai 1996, 13(1): 14-20.  Abstract ( )   PDF (428KB) ( )   This paper presents a calculating method for tracing the moving phase-interface.The essential idea is that the von-Neumann numerical method is used in the region far from the phase-interface.In both sides close to phasc-interface a special difference scheme is established by using Rankine-Hugoniot jumping conditions and some characteristics of hyperbolic equations of fluid dynamics.

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ANALYSIS OF THE FINITE DIFFERENCE BEAM PROPAGATION METHOD Yang Jianyi, Feng Hao, Wang Minghua 1996, 13(1): 21-28.  Abstract ( )   PDF (538KB) ( )   A finite difference beam propagation method (FD-BPM) is analyzed and assessed for the application to two-dimensional structures.The general formulations for the FD-BPM are derived form Maxwell equations for TE mode and TM mode respectively,with the transparent boundary condition (TBC).The FD-BPM is assessed by computing the loss caused by the numerical error and the percentage error of the propagation constants of the TE and TM modes of a step-index slab waveguide.Based on this assessment,FD-BPM appears to be a good tool for the analysis and simulation of the optical waveguide devices and a exellent method for the computer-aided-design in Integrated Optoelectronics.

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NUMERICAL SIMULATIONS OF NATURAL VENTILATION ON TWO-DIMENSIONAL LAMINAR-FLOW IN HOUSING UNIT Wang Zhengxian, Lai Dingwen, Wang Jian, Wei Zhaoji, Li Qunhong 1996, 13(1): 29-37.  Abstract ( )   PDF (776KB) ( )   A numerical approach is presented for simulating the quality of natural ventilation in an apartment unit with three bedrooms and one hall by using algorithm of Simpler and Artificial compressing method based on blocked interior spaces,which obtained the main data on the distribution of laminar-flow field in a housing unit. The application software created accordingly applies universally,which provides an effective means for an alyzing,optimizing and evaluating the quality of natural ventilation in housing design.

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SOME BASIC PROPERTIEW OF VIRCATOR GENERETING MICROWAVE Wang Min, Li Jing 1996, 13(1): 38-42.  Abstract ( )   PDF (342KB) ( )   The Vlasov-Poisson equations are used to simulate the propagation processes of relativistic electron beam (REB) in one plate or two plates.The position of cumulative maximum space charge,the oscillating frequency,of current J,elrctron number density n and electric field E in different positions versus injecting electron number density n0 and injecting electron velocity v0 in one plate model,and the inject-ing current J0 and the distance between the two plates in two plates model are investigated.Numerical results of virtual cathode position are closed to the results given by stable theory.Its oscillating frequency is in agreement with the empiric expresion (1~√2π)ωpeb.Numerical simulation result for injecting elec-tron beam density having Guass distribution for volecity,spread of energy ΔEn/En < 10% appears to be in largely conformity with the conclusion of monoenergy case in one plate model.

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A GODUNOV-TYPE DIFFERENCE METHOD WITH HIGH RESOLU TIONFOR 2-DIMENSIONAL UNSTEADY MULTI-MATERIAL FLOW Li Yinfan, Yu Tong 1996, 13(1): 43-49.  Abstract ( )   PDF (421KB) ( )   A Godunov-Type difference method with high resolution on non-uniform rectangle mesh for 2-dimensional Unsteady Multi-material flow is described.A Simple method for representing interfaces is also introduced.Results of several numerical examples are presented and have displayed the efficiency of this method.

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A SIMPLIFIED NUMERICAL METHOD fOR CALCULATING 3-D RADIATION FIELD OF CAVITY Feng Tinggui, Lai Dongxian 1996, 13(1): 50-56.  Abstract ( )   PDF (529KB) ( )   Based on a simplified physics model a numerical method is proposed for calculating 3-D radiation field of cavity and the convergence of iteration procedure used is discussed.In order to illustrate that the method is feasible and effective,some numerical examples are given as well.

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HIGH RESOLUTION SCHEME FOR MULTI-COMPONENT FLUID DYNAMICS Li Deyuan, Shui Hongshou, Dong Suqin, Feng Xiaosi 1996, 13(1): 57-64.  Abstract ( )   PDF (436KB) ( )   Harten's TVD scheme (1983) is sucessfully applied to the 1-D Lagrangian fluid dynamic equations,where not all the physical variables are discretized on the same point.A high resolution non-conservative scheme for multi-material system is given.Numerical experiments are presented to demonstrate the performance of these schemes.

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CHARACTERIZATION OF TIME SERIES RECONSTRUCTION WITH TWO VARIABLES OF DYNAMIC SYSTEM Yang Zhian, Chen Shigang, Wang Guangrui 1996, 13(1): 65-72.  Abstract ( )   PDF (838KB) ( )   The second order Jacobian J2 is calculated to determine the delay time T of two-dimensional reconstruction about ordinary differential equation according to the first extreme value of J2.This method gives more information of reconstruction than orhter methods.As an example,the forced Brusselator system is discussed.

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NUMERICAL SIMULATIONS OF VORTEX MOTION PATTERNS IN OSCILLATING FLOW AROUND A CIRCULAR CYLINDER Ling Guoping, Ling Guocan 1996, 13(1): 73-78.  Abstract ( )   PDF (607KB) ( )   A new hybrid finite difference and vortex method,which is based on domain decom-position and proposed by the authors,is used for calculating the oscillating flow around a circular cylinder at various Keulegan-Carpenter numbers (Kc=2~24) respectively.The rules of variation of vortex motion patterns with Kc numbers are studied systematically.The vortex motion patterns in asymmetric regime,single pair (ortransverse) regime,double pair (or diagonal) regime and three pairs regime are first successfully simulated in China.The calculated drag and inertial coefficients are in better agreement with experiments than other recent numerical results.

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OPTICAL FIELD DISTRIBUTION AND POLRIZED MODE IN WIDE PLANAR-WAVEGUIDE Xu Qiyang, Song Yixin, Wang Xinbing, Yang Kecheng, Zu Xiao, Xie Minje, Li Zaiguang 1996, 13(1): 79-86.  Abstract ( )   PDF (532KB) ( )   The optical field distribution in wide planar-waveguide CO2 gas laser satisfies Helmholtz equation.Under certain given conditions,expressions of the polarized modes EHnmx and EHnmy are obtained by solving optical field distribution equation.The present computation gives a normalized theoretical distribution curve of EH1.16 polarized mode existed in 3×18mm2 waveguide discharge area.The curve is consistent with the experimental results.

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PADE'APPROACH IN THE FEL'S NUMERICAL SIMULATION Zhang Zhichou, Yao Jun 1996, 13(1): 87-91.  Abstract ( )   PDF (268KB) ( )   Higher-order accuracy schemes are established following PADE' approach.Based on the schemes,fast recursive algorithms for the simple equations.Can be obtained and satisfy the corresponding conservation law.The fast recursive algorithm in the reference [1] is a kind of specific form of the present recursive algorithms given here.

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AN ALGORITHM TO CALCULATE FIRST AND SECOND ANALYTICAL DERIVATIVES IN LENS OPTIMIZATION DESIGN Feng Qibo 1996, 13(1): 92-100.  Abstract ( )   PDF (550KB) ( )   A novel algorithm to calculate first and second derivatives in lens optimization design is described.Based on the differential law of complex function,the first and second analytical derivatives of ray coordinates in the image plane with respect to parameters such as radius,thickness etc.can be obtained from only one raytracing.On the basis of this,the first and second derivatives of the merit function with respect to variables can be easily obtained.The relevant deduction process and examples of computation are also given.The results of practical computations show that it takes much less time (especially for the second derivatives) to obtain the derivatives by the analytical method than by the difference method.

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STUDIES ON THE MAGNETIC PROPERTIES OF ThMn12(YFe12) WITH THE DV-Xα METHOD Qi Shouren, Tang Chengchun, Huang Xintang, Zhang Yan, Li Yongping, Zhang Haifeng 1996, 13(1): 101-104.  Abstract ( )   PDF (269KB) ( )   DV-Xα method,is applied for calculating the Electronic structure and Magnetic properties of YFe12,which is an ideal structure of ThMn12.The result shows that this method has satisfactory advantages on the theoretic of magnetic material.

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NUMERICAL PROBLEMS OF THE MAGNETIC FIELDS ON AN AXISYMMETRIC MODEL Mou Zongze, Miao Jing, He Qibing, Jian Guangde, Li Huanxing, Luo Xinjun 1996, 13(1): 105-111.  Abstract ( )   PDF (344KB) ( )   The oscillating solutions of the magnetic fields may arise on an axisymmetric model by using first order finite elements.In addtion,they may also occur for nonuniform grids.The paper analyses the cause of forming oscillating solutions and the behaviour of oscillating solutions.The methods of cancelling the oscillation are suggested.

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MICROCOMPUTERIZED FOR LARGE COMPUTING FLUID ANALYSIS PROGRAM AND ITS APPLICATION Mei Liquan, Wang Weidong, Hung Aisiang 1996, 13(1): 112-114.  Abstract ( )   PDF (232KB) ( )   FIDAP software Package is the first genaral software for simulation of incompressible viscous flow by using the finite element method.There are 120000 Fortran senterces in it,A brief introduction is given for its theorical models and algorithm functions,the treatment tricks for implanting FIDAP into a PC computer are given also.

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PROPAGATION CHARACTERISTICS OF DARK SOLITON STUDY IN OPTICAL FIBERS WITH SLOWLY DECREASING DISPERSION Shen Tinggen 1996, 13(1): 115-118.  Abstract ( )   PDF (242KB) ( )   The solution of non-linear schr6diuger (NLS) equation including twophoton absorption in optical fibers with slowly decreasing dispersion,is given by using travelling wave method,and the solution for the propagation characteristics of dark soliton is also discussed in detail.

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GENERALIZED FINITE ELEMENT METHOD FOR TWO DIMENSIONAL TRANSONICFLOW IN TURBOMACHINEARY Zhu Gang, Shen Mengyu, Liu Qiusheng, Wang Baoguo 1996, 13(1): 119-123.  Abstract ( )   PDF (433KB) ( )   One kind of Generalized Finite Element Method-Taylor-Galerkin has been improved on convergences of velocity and stability.Using the improved method two dimensional transonic flow in turbomachinery is studied.Numerical results compared with that of experiment exhibit the advantages of this method.

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DY-AN INTERACTIVE PROGRAM FOR CALCULATING VARIOUS DYNAMICAL BEHAVIOURS OF THE NONLINEAR DYNAMICAL SYSTEMS Fang Haiping 1996, 13(1): 124-128.  Abstract ( )   PDF (434KB) ( )   An interactive program is presented for numerically calculating various dynamical behaviour for the nonlinear dynamical systems which can be expressed as ordinary differential equations or maps. This program facilitates visual exploration of various visual behaviour such as the phase space,Poincare section,manifolds,bifurcation diagram and power spectrum,etc.by providing a set of visually oriented operation on graphic objects.