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25 March 2002, Volume 19 Issue 2 Previous Issue    Next Issue

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A NUMERICAL STUDY OF A TWO-STAGE 4K-PULSE TUBE CRYOCOOLER JU Yong-lin, de WAELE A T A M 2002, 19(2): 95-102.  Abstract ( )   PDF (341KB) ( )   A new mixed Eulerian-Lagrangian computational model for simulating and visualizing the internal processes and the variations of dynamic parameters of a two-stage 4K pulse tube cryocooler operating at liquid helium temperature region is developed.The Lagrangian method,a moving grid, is used to follow the exact tracks of gas particles as they move with the pressure oscillation in the pulse tube to avoid any numerical false diffusion.The Eulerian approach,a fixed computational grid,is used to simulate the variations of dynamic parameters in the regenerator.A variety of physical parameters,such as real thermal properties of helium,multi-layered magnetic regenerative materials,pressure drop and heat transfer in the regenerator and heat exchangers,are taken into account. The detailed time-variations of gas temperature,pressure,mass flow rate,enthalpy flow in a cycle,in the first and the second-stage regenerators are presented.Attention is also paid to the effects of different regenerative materials on the performance of the 4K two-stage pulse tube cooler.

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AN IMPROVED METROPOLIS APPROACH TO THE DISCRETE-STATE SYSTEM WU Jin-shan, BAO Jing-dong, YANG Zhan-ru 2002, 19(2): 103-107.  Abstract ( )   PDF (177KB) ( )   An improved Metropolis approach is proposed especially to solve the equilibrium problem of a discrete-state system, used to deal with the Ising model and proven to be well consistent with the traditional Metropolis method. But it's more efficient as it reduces 25 percent of the simulating time. Especially for the Ising model, the Master equation is generalized in the simulation. This kind of Master equation of critical kinetics and its' transient phenomena can effectively be studied by using the modified Metropolis method presented here.

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LARGE EDDY SIMULATION OF R-T INSTABILITY AND TURBULENT MIXING XIE Zheng-tong, LI Jia-chun, WANG Li-li 2002, 19(2): 108-114.  Abstract ( )   PDF (462KB) ( )   The Rayleigh-Taylor instability is numerically studied through the Large-Eddy-Simulation (LES) approach.The whole evolution process of the instability is achieved,including the linear stage,the regular nonlinear stage,the irregular nonlinear stage and the turbulent mixing stage.The characteristic of the interfacial motion and the growth of the mixing layer thickness are analyzed.And the averaged turbulent energy as well as the flux of passive scalar is calculated at both the resolved scale and the subgrid scale.The LES method is proved to be an effective approach for the simulation of the Rayleigh-Taylor instability.

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STABILITY ANALYSIS AND TRANSITION PREDICTION FOR BLUNT-CONE FLOW LIU Hong, WANG Fa-min, LIU Jia, YAO Wen-xiu, LEI Mai-fang 2002, 19(2): 115-120.  Abstract ( )   PDF (244KB) ( )   Numerical method for stability analysis and transition prediction for supersonic flow around a blunt cone is investigated. In order to meet the required accuracy of the numerical values in the basal flow field, the result of the flow field is obtained by solving Euler equations where the pressure attribution on the surface of the cone is used as the outer edge pressure attribution of the viscous boundary layer. The Rayleigh inverse-iteration method and boundary layer asymptotic expansion method are used to solve the blunt cone boundary layer stability equation to get reliable boundary layer transition data. This method improves the numerical precision, and saves the computation time. It is also useful for stability analysis of blunt cone supersonic flow.

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THE FAST AND STABLE ALGORITHMS FOR THE NUMERICAL INVERSION OF BLACK BODY RADIATION LI Cui-huan, XIAO Ting-yan 2002, 19(2): 121-126.  Abstract ( )   PDF (220KB) ( )   By using the Tikhonov Regularization Method,the related techniques for the numerical inversion of black body radiation are discussed.The special interest focuses on the presentation and experiment of some new and hybrid algorithms,which generate a good starting-up strategy separately with Newton method and a 3-order-convergence iterative scheme of solving the Morozov discrepancy equation to determine the regularization parameter.The numerical test is also made to illustrate the high efficiency and good stability of the proposed algorithms.

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SMALL-SIGNAL MODEL PARAMETER EXTRACTION FOR POWER GaAs MESFET's WU Long-sheng, LIU You-bao 2002, 19(2): 127-131.  Abstract ( )   PDF (182KB) ( )   The intrinsic elements are described as functions of the extrinsic parameters.Those relative errors of intrinsic elements are proposed as objective functions.Extrinsic element values of FET's at unbiased state are used as the initial values of the independent variables.Then the intrinsic element values of ‘hot’ FET's are extracted with the optimization method.The results show that the relative errors of S-parameters are 0.09% for S11,1.1% for S12,0.08% for S21,2.26% for S22,respectively.The key properties of the method are fast convergence,high precision and efficiency.It is easy to transplant the optimization method into microwave CAD tools for circuit design and simulation.

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TRANSMISSION OF SHORT WAVELENGTH LASER WITH THE TRANSVERSE MULTIMODE IN CAVITIES WITH CIRCULAR MIRRORS OF SPHERICAL SURFACES FU Han-qing, WANG Tai-chun 2002, 19(2): 132-136.  Abstract ( )   PDF (193KB) ( )   Fresnel integral equations of the transverse multimode are solved by the numerical integration method in the cylinder coordinate. Under the initial conditions of the uniform and random distribution given respectively for the complex light-field amplitude, TEMn0 modes of the confocal and stable cavities with circular mirrors of spherical surfaces as well as the plane cavity with circular mirrors are computed and analized. Computational results indicate that the numerical results of single mode for spherical cavity coincide with the analytical results. The results of the multimode not only conform to the behavior of the multimode space distribution, but also show that those of the fundamental mode dominate.

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NUMERICAL STUDY ON THE DAMAGING OF CONCRETE AND ROCK IN THE HIGH VELOCITY IMPACT CAO Ju-zhen, LI En-zheng, WANG Zheng 2002, 19(2): 137-141.  Abstract ( )   PDF (304KB) ( )   The constitutive model and its parameters of concrete and rock with damaging variables are given referring to[1,2],and coded into a 2-D elastic-plastic finite element program named LTZ-2D.With this program,the problem of projectile and kinetic bullet penetrating concrete and rock targets is numerically simulated.The results of simulation are compared with those of experiments.

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FINITE ELEMENT ANALYSIS ON TRAFFIC FLOW PROBLEM (Ⅱ) ZHANG Peng, LIU Ru-xun 2002, 19(2): 142-148.  Abstract ( )   PDF (289KB) ( )   By taking the numerical method and traffic phenomena into account, reasonable improvement is attained on the kinetics equation of the L-W theory. The comparison between what is deduced from the original model by means of characteristics and discontinuity analysis and what is shown by the numerical results of the improved model is made, which further reveals that the latter is the approximation of the former and that such results are convincing. Numerical examples include such problems as red-and-green and traffic accidents, which concern mixed density distribution from the minimum to the maximum, lane changing and a quick density increase or decrease on the boundary and which are also considered most challenging in the field.

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NUMERICAL MODELING OF SIGNORINI PROBLEM BASED ON DUAL MIXED VARIATIONAL PRINCIPLE WANG Guang-hui, WANG Lie-heng 2002, 19(2): 149-154.  Abstract ( )   PDF (199KB) ( )   Based on the dual mixed variational formulation for the Signorini problem,a nonconforming finite element method is proposed.The discrete B-B condition is confirmed and the error estimation O(h3/4)for Raviart-Thomas(k=0)finite element is achieved.A Uzawa type algorithm is used for solving the Signorini problem which is discretized by conforming finite element method as well as nonconforming finite element method.The accuracy and efficiency of both are demonstrated by numerical results.By contrast to the conforming one,nonconforming method is more cost-effective.

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DAMPING GAUSS-NEWTON METHOD AND ITS APPLICATION TO THE INVERSION OF HIGH FREQUENCY ELECTROMAGNETIC WAVE LOGGING ZHANG Mei-ling, XING Guang-long, LIU Man-fen, YANG Shan-de 2002, 19(2): 155-158.  Abstract ( )   PDF (185KB) ( )   Gauss-Newton optimization technique is a method with less computation time and rapid convergence speed, but it requires better initial conditions. It is a tickler to lose its role or to bring about local-extreme-value problems. Under the circumstances, an improved damping form of Gauss-Newton optimization technique is presented to avoid these problems. By using the diagonal damping matrix, the damping role will be changed according to the relative modified amounts of the inversion parameters. The good effect is obtained when this approach is used in the inversion problem of the high frequency electromagnetic wave logging.

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DISSIPATION AND ALGEBRAIC SOLITARY LONG-WAVES EXCITED BY LOCALIZED TOPOGRAPHY MENG Lu, LÜ Ke-li 2002, 19(2): 159-167.  Abstract ( )   PDF (332KB) ( )   An inhomogeneous Benjamin-Davis-Ono-Burgers equation including topographic forcing and turbulent dissipation is derived in terms of the quasi-geostrophic vorticity equation, an approximate analytic solution of the BDO-Burgers equation with a small dissipation is obtained, the time variations of mass and energy of the algebraic solitary waves are discussed, and finally, the forced BDO-Burgers equation is integrated numerically and the numerical solutions are given for a given basic flow with a weak shear and a localized topographic forcing.

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THE APPLICATION OF MONTE CARLO METHOD IN SINGLE EVENT UPSET SIMULATION LI Hua, CHEN Shi-bin 2002, 19(2): 168-172.  Abstract ( )   PDF (193KB) ( )   The Monte Carlo method is used in the single event simulation which describes the processes of the particle transportation and the random sampling. Particularly, the single event upset of a silicon chip induced by 14*!MeV neutrons at a random incident angle is calculated and analyzed. In the mean time, the Monte Carlo error is also considered. By the Monte Carlo method, some information about the physical mechanism of the single event upset is provided.

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AN INVESTIGATION OF AIRFOIL FLUTTER CHARACTERISTICS WITH STRUCTURE NONLINEARITY AT TRANSONIC SPEED YANG Yong-nian, YE Zheng-yin 2002, 19(2): 173-176.  Abstract ( )   PDF (150KB) ( )   An analysis method of the airfoil flutter system with nonlinear structure at transonic speeds is presented. The unsteady aerodynamic forces are calculated by Navier-Stokes equations. The time histories of structure responses of airfoil are solved by coupling the Navier-Stokes equations and flutter equations. The systems with gap stiffness, cubic type stiffness and cubic structure damping are investigated. The calculated results show that the influence of the structure nonlinearity on flutter speed is sensitive. Due to both the structure and aerodynamic nonlinearity in the flutter system, the oscillation characterstics become very complex.

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DYNAMICAL CHARACTERISTICS OF DOUBLE POROSITY/DOUBLE PERMEABILITY MODEL INCLUDING THE EFFECT OF QUADRATIC GRADIENT TERM TONG Deng-ke, CAI Lang-lang 2002, 19(2): 177-182.  Abstract ( )   PDF (189KB) ( )   Traditional well-test models for flow are not consistent with the material balance equation. According to the assumption of slightly compressible fluid, the quadratic gradient term in the nonlinear partial differential equation is usually neglected. It is known that neglecting the quadratic gradient term results in errors for large time well-test. A method which is consistent with the material balance equation for fractured reservoir with double porosity/double permeability is proposed. All terms in the nonlinear partial differential equation are retained. Double porosity/double permeability models are given. The numerical solutions of double porosity/double permeability models are obtained by the Douglas-Jones predictor-corrector method at a constant rate and the constant-pressure production for an infinitely large system. It also deals with the change rule of pressure while fluid compressibility and double porosity parameters change. Plots of the typical pressure curves are given, and the results can be applied to the well-test analysis.

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OMPUTER SIMULATION OF STIM SUN Min-de, LIU Bo, SHI Xian-feng, SHEN Hao, MI Yong 2002, 19(2): 183-188.  Abstract ( )   PDF (612KB) ( )   The theory model of STIM simulation is reported here.A related computer program which runs on Windows 9X/NT is written by the fourth generation Object-Oriented Programming (OOP) language C++.With its friendly interface,some parameters can be easily changed,such as detector resolution,scanning scale and elemental distribution of specimen.Automatically 360° rotation can be achieved and any rotary angle in experimental condition can be simulated.With multithread processing,the program runs faster and can be paused or stopped at any moment.The result of some examples are showed and discussed.