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25 March 2001, Volume 18 Issue 2 Previous Issue    Next Issue

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FINITE VOLUME METHODS FOR SOLVING THE PROBLEM OF DISCONTINUOUS SOLUTION WANG Ji-wen, LIU Ru-xun 2001, 18(2): 97-105.  Abstract ( )   PDF (342KB) ( )   A speedily developed numerical method called as finite volume method (FVM),which possesses both merits of finite difference method and finite element method,is devoloped.The construction of FVM for conservation laws is introduced.Especially,some efficient and successful schemes for solving the discontinuous problems are discussed in detail.Moreover,several numerical results of simulation of 2D dam break problem are given.Finally,a summary of advances in numerical applications and theoretical analysis of FVM is presented.

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DIRECT SIMULATION OF THE LINEAR INSTABILITIES IN COMPRESSIBLE SHEAR LAYERS WANG Qiang, FU De-xun, MA Yan-wen 2001, 18(2): 106-110.  Abstract ( )   PDF (185KB) ( )   The linear instabilities in compressible shear layers are investigated by solving the two and three dimensional time dependent compressible Navier Stokes equations.A high accuracy upwind/symmetric compact difference hybrid algorithm is used.A pseudo random number generation technique is employed to simulate the white noise disturbance.Based on numerically solving the three-dimensional viscous disturbance equations by using a new method named as SCD-MNR,some results related to linear stability analysis are first given.Both two-and three-dimensional waves are considered.Compressibility effect can increase the most unstable wave angles besides that damps the growth rates of unstable waves.Numerical results confirm the prediction of linear theory that during the initial evolution of the compressible shear layer unstable waves are linear,and that in this course the wave number and angle of the most unstable disturbance are selective.The algorithm used here appears to be effective.It is a reasonable means for the study on compressible shear layers that linear theory combines with numerical simulation.

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A NUMERICAL STABILIZATION METHOD FOR NONLINEAR ANALYTIC NODAL METHOD FU Xue-dong, LIU Cheng-an 2001, 18(2): 111-114.  Abstract ( )   PDF (126KB) ( )   The nonlinear analytic nodal method require analytic solutions of the two-node problems,in which the numerical instability problem might be encountered due to the ill-conditioned algorithm for finding the particular solution of near-critical node.To address this problem,a stabilization method is developed by applying the method of variation of parameters and linear approximation to the near-critical node calculations.Numerical results demonstrate the effectiveness of the method.

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APPLICATION OF RADON TRANSFORM IN INVERSE PROBLEM OF PERMEABILITY DYNAMICS LI Xiao-feng, ZHU Ben-ren 2001, 18(2): 115-118.  Abstract ( )   PDF (153KB) ( )   The inverse problem of elliptic partial differential equation in the permeability field is discussed,whose permeability coefficient is nearly uniform.By using Radon transform in computerized tomography technology,the solution to this problem could be found,and some numerical examples are presented.

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COMPUTATION OF NATURAL CONVECTION IN TWO DIMENSIONAL CAVITY USING SPECTRAL ELEMENT METHOD QIN Guo-liang, XU Zhong 2001, 18(2): 119-124.  Abstract ( )   PDF (220KB) ( )   A spectral element method for the computation of nature convection in closed square cavity is presented.The incompressible Navier Stokes equations expressed in terms of the primitive variables velocity and pressure,and an additional equation for the temperature,are considered.All the variables are expanded in Chebyshev polynomials.A time splitting method is used with a fourth order Runge Kutta for the nonlinear terms and a semi implicit Crank Nicolson method for the viscous terms.The obtained results show to be in excellent agreement with the accepted benchmark solutions.

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NUMERICAL CALCULATION OF NATURAL CONVECTION FLOWS ON SEMICIRCULAR CAVITY WANG Xu, GU Chuan-gang 2001, 18(2): 125-128.  Abstract ( )   PDF (161KB) ( )   It presents details of the results of natural convection flows for Ra≤107 on semicircular cavity.The control volume finite element method based on unstructured grids and mass weighted upwind scheme is employed to discretize governing equations, and the fronts method is employed to solve the pressure discretization equations.For all of Ra≤105, the present results are very agreement with the previous literature, and for Ra=106、107, the iterations have not run into the difficulty of convergence.

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A VOLUME-WEIGHTING CIC METHOD FOR NUMERICAL SIMULATION OF AXIAL SYMMETRICAL PLASMAS LIU Chun-liang, ZHANG Xiao-jin, LI Yong-dong, LIANG Ying-liang 2001, 18(2): 129-132.  Abstract ( )   PDF (122KB) ( )   A volume weighting CIC method is developed to compute the node charges and currents in PIC simulation of axial symmetrical plasmas.A set of formulae for computing the node charges and currents is derived.The results given here can be applied to 2(1/2) dimensional electrostatic and electromagnetic PIC simulation of axial symmetrical plasmas.

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HIGH-RESOLUTION SHOCK CAPTURING SCHEME AND ITS APPLICATION IN CFD ZHAO Xing-yan, SU Mo-ming, MIAO Yong-miao 2001, 18(2): 133-137.  Abstract ( )   PDF (170KB) ( )   It aims to extend high resolution AUSMPW shock capturing scheme to the multidimensional hyperbolic conservation laws in curvilinear coordinates.The third order MUSCL shceme with Van Leer limiter is used to extend the basic first order AUAMPW scheme to third order spatial accuracy for all test cases.The equations are discretized by using a finite volume method.The present scheme combined with the LU SGS scheme is applied to compressible inviscid and viscous flows.The computed results are compared with the experimental data or the other numerical results available in literature and good agreements between them are obtained.The AUSMPW scheme is also compared with CD, TVD, FVS and FDS schemes.

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ANALYZING POLLUTION PATTERN IN SEAWARD FIRTH OF JIAOLU JIANG WITH A NUMERICAL METHOD OF NONLINEAR DIFFUSION WANG Xiang-san 2001, 18(2): 138-142.  Abstract ( )   PDF (164KB) ( )   On the basis of analyzing the flow regime and pollution pattern of the sea area of Jiaolu Jiang Firth, the pollutant nonlinear diffusion phenomenum in the seaward firth with mixed up salt and fresh water is studied.The finite element method is used for conducting numerical analysis and the stability of the numerical solution is also investigated.Comparing the calculation data with the measured one, it is shown that the obtained result has better accuracy.This paper treats seaward firth as a dynamic system, divide the solution domain into finite elements and find the solution by a punitive function,variable size combinatorial method and non-linear optimization solution.In order to ensure solution stability,use non-dimension variables and take time-step as control condition.

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THE SPARSE CODING STRATEGY EMPLOYED BY SIMPLE CELLS IN VISUAL CORTEX V1 YANG Qian, QI Xiang-lin, WANG Yun-jiu 2001, 18(2): 143-146.  Abstract ( )   PDF (140KB) ( )   The spatial receptive fields of simple cells in mammalian striate cortex have been characterizd as being localized,oriented,and band pass detectors.These receptive fields produced a sparse distribution of output activity in response to natural image.It shows a model of sparse coding with overcomplete basis sets in the population of simple cells from the physical process of image detection,and gives coding representation of image in realistic visual environment.

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INFLUENCE OF THE SQUEEZED ANGLE ON THE SQUEEZING EFFECT OF MESOSCOPIC COUPLED CIRCUIT JI Ying-hua, LEI Min-sheng 2001, 18(2): 147-151.  Abstract ( )   PDF (162KB) ( )   Starting from the classical motion equation of a non-dissipative mesoscopic inductance coupled circuit with source, it investigates the fluctuations of the charge and current in the mesoscopic inductance coupled circuit at the squeezed vacuum state, and study especially the influences of the squeezed angle on the fluctuations.The results indicate if the system is in the squeezing vacuum state, the quantum fluctuations of both circuits are related reciprocally but the fluctuations are independent with the source.Also,the squeezed effect of the charge and current is depended on the squeezing parameter γ and the squeezing angle θ as well.Moreover, the fluctuation of the charge and current does not monotonously decrease in an arbitrary squeezed angle θ , instead of has a minimum.

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NUMERICAL METHOD OF ION TRANSPORT IN ECR MICROWAVE PLASMA WITH PLANAR AND CYLINDER MODELS GONG Ye, SONG Yuan-hong, WEN Xiao-jun, DENG Xin-lu 2001, 18(2): 152-156.  Abstract ( )   PDF (158KB) ( )   Monte Carlo method is used to simulate such a complete course, in which the ions pass through the neutral region, the sheath, and the shield region of a virtual cathode formed by secondary electrons near the workpiece surface, finally come to be absorbed by the surface of the workpiece with negative bias in ECR microwave plasma.Discussion covers the connection problem of neutral region and sheath at the sheath edge.The non linear Poisson equation is solved with "trial" method, and results in smooth and self consistent spectrum of potential and distributions of ion energy and angle at the surface of workpiece.

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COMPUTATIONAL STUDY OF UNSTEADY VISCOUS FLOW AROUND AN IN-LINE OSCILLATING CIRCULAR CYLINDER IN A UNIFORM FLOW LIU Song, FU Song 2001, 18(2): 157-162.  Abstract ( )   PDF (245KB) ( )   A finite volume method is presented for the time dependent viscous incompressible flow around an in line oscillating circular cylinder at Reynolds number of 200、855 and 4 000.The N S equations in finite volume form are solved on a moving grid system, based on a time dependent coordinate transformation.To investigate the vortex shedding characteristics behind the circular cylinder and the effects of Reynolds number and other non dimensional parameters such as reduced amplitude and reduced frequency,several numerical schemes have been tested with different amplitudes and frequencies at each Reynolds number.Present numerical results indicate that several types of vortex shedding modes are mainly dependent on the reduced frequency and also the reduced amplitued,which is called synchronization or lock on.

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THE GHOST METHOD FOR FLUID INTERFACE INSTABILITY IN 3D TANG Wei-jun, ZHANG Jing-lin, LI Xiao-lin, ZHAO Ning 2001, 18(2): 163-169.  Abstract ( )   PDF (222KB) ( )   It uses a Level Set function to track the motion of a fluid interface in an Eulerian framework.In addition,the use of Ghost cells (actually Ghost nodes in the difference framework) can keep the density profile from smearing out,while still preserving the scheme robust 2-nd easy to program with and accuracy TVD scheme in spacial and two step Runge Kutta methods.In contrast, the references[6][7] allow the density profile smearing out.This method significantly improves the resolution at the contact discontinuity.

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THE WAVE PACKET EVOLUTION SIMULATION OF THE I-V PROPERTY OF NANOPARTICLE SELF ASSEMBLY SYSTEMS HE Hong-bo, Zhou Ji-cheng, HU Hui-fang, LI Yi-bing 2001, 18(2): 170-172.  Abstract ( )   PDF (98KB) ( )   The current voltage characterization of a standard double barrier tunneling junctions (DBTJ) which forms room temperature single electron devices is computed by means of time-dependent Schrödinger equation.For Au nanoparticles self assembly systems at room temperature it is simulated by wave packet evolution method.It is found that the simulated results are in good agreement with the experimental ones.This numerical method is proved to be of importance for the experiment and realization of the nanostructure devices.

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FIVE MONTE CARLO METHODS FOR SIMULATION OF DYNAMIC RELIABILITY SYSTEM Xiao Gang, LI Tian-duo, YU Mei 2001, 18(2): 173-176.  Abstract ( )   PDF (118KB) ( )   Based on integrated description of simulation of dynamic reliability system, algorithms of direct simulation, analog simulation, forced transmit, direct statistical extimation, weighted statistical estimation are given.Reliability of a non markov Con/k/n:F system is calculated by these five Monte Carlo methods.Results show that weighted statistical estimation method has highest efficiency.

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THE PARALLEL DESIGN OF MONTE CARLO CODE AND MEASURES OF ENHANCE SPEEDUP DENG Li, XIE Zhong-sheng, HUANG Zheng-feng, XU Hai-yan 2001, 18(2): 177-180.  Abstract ( )   PDF (111KB) ( )   The parallel design of Monte Carlo code involves computational method and module designs,which is crucial to the parallel efficiency.The coupled of neutron and photon transport Monte Carlo code MCNP has been realized the parallelization in PVM and MPI by modifying the serial code.Due to the form having module being optimized, the parallel efficiency is good where the efficiency of MPI code is stronger than that of PVM code and the speedup of MPI code is higher than that of PVM in most cases.The calculated results of parallel code are reasonable.Both the speedups of PVM code and MPI code have been the linear increasing with the processors.The parallel efficiencies are up to 99% in 16-processors,97% in 32-processors and 89% in 64-processors respectively.

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A NONUNIFORM LATTICE BOLTZMANN METHOD BASED ON DOMAIN DECOMPOSITION GUO Zhao-li, SHI Bao-chang, WANG Neng-chao 2001, 18(2): 181-184.  Abstract ( )   PDF (146KB) ( )   A lattice Boltzmann model (LBM) with nonuniform mesh is proposed based on domain decomposition technique.The basic idea is to divide the flow domain into some regular subdomains,and then perform simulations on each subdomain using LBM with uniform mesh.The values on the boundaries of the subdomains are determined by interpolation.The 2-D flow around a cylinder is simulated using the model,the results are also compared with those of other methods.

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THE NUMERICAL METHODS OF THE RESEARCH IN THE ORBITAL EVOLUTION OF THE ASTEROIDS LIU Lin, JI Jiang-hui, LIAO Xin-hao 2001, 18(2): 185-188.  Abstract ( )   PDF (115KB) ( )   The asteroids are the most important small bodies in the solar system,and they mainly lies in the two locations-a main belt between the Mars's orbit and the Jupiter's and the near Earth space.The most feature of the orbits of Near Earth Asteroids (NEAs) is that the semi major axes of the orbits are nearly equal to that of the Earth or the perihelia distances are approximate to or even less than the mean distance between the Sun and the Earth,thus they could move into inside of the Earth's orbit,so that they might close approach or even colliside with the Earth (or other planets,such as the Venus,the Mars,etc.).The characteristic brings about some difficulties in the numerical research during their orbital evolution,which leads to the failure of the normalization technique in the general removal impact singularities of celestial mechanics methods and the Symplectic Algorithm which is successfully applied to the investigation in quality.By comparing the computation effects of several common numerical methods (including Symplectic Algorithm),and considering the nature of the movement of the small bodies,the corresponding treatments are provided here to improve the reliability of the computation.

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LOGISTIC MODEL WITH GATE FENG Guo-iin, CAO Hong-xing 2001, 18(2): 189-192.  Abstract ( )   PDF (137KB) ( )   The system boundary which plays a role in:Ι defending the existence of the system; and Ⅱ exchanging between the system and its environment is defined as a shell (Jieke).Some basic concepts in Jieke theory are described.Some applications of the theory are presented too, in particular,considering switch function of the gate in system, a new discrete logistical model is established.Mapping calculation for the model was conducted.Then nonlinear features of the model with parameter variation were analyzed and irrational numbers and cyclic small numbers are obtained.