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25 November 2002, Volume 19 Issue 6 Previous Issue    Next Issue

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A NEW SIMPLIFIED GAS-KINETIC BGK SCHEME LI Qi-bing, FU Song 2002, 19(6): 471-475.  Abstract ( )   PDF (177KB) ( )   A newly developed gas-kinetic BGK scheme is further simplified. Numerical tests show that the new simplification not only keeps the advantages of the old scheme, such as its robustness and automatic satisfaction of the entropy condition but also makes the scheme simpler and more efficient.

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APPLICATION OF BGK SCHEME ON UNSTRUCTURED MESHES SUN Xi-ming, YANG Jing-long, YAO Zhao-hui 2002, 19(6): 476-482.  Abstract ( )   PDF (417KB) ( )   A BGK model on the 2D adaptive unstructured mesh is developed within a finite volume framework, which consists of two steps:the solution reconstruction step and the gas evolution step. The computation domain is tessellated with triangular elements. In the reconstruction step, a high-order ENO scheme based on the least-square principle is employed to obtain the derivatives. In the gas evolution step, with the axis rotation, the flux through each side of the triangular element is obtained. Some test cases validate the capability of the current numerical approach to provide a highly accurate solution in complex geometries. It is observed that the BGK model provides a reasonable alternative to Riemann solvers.

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LATTICE BOLTZMANN SIMULATION OF DOUBLE DIFFUSIVE NATURAL CONVECTION GUO Zhao-li, LI Qing, ZHENG Chu-guang 2002, 19(6): 483-487.  Abstract ( )   PDF (348KB) ( )   A lattice Boltzmann model is proposed for the double diffusive natural convection system.The flow in a square cavity driven by a temperature gradient and a concentration gradient is then simulated using the present model.The influence of the concentration field on the flow patterns is investigated,and some quantitative comparisons with other studies are made.It is shown that the present LB model can predict the flow characteristics correctly.

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SIMULATION OF SCATTERING WAVES IN 2-D COATED AERODYNAMIC SHAPES CHEN Hong-quan, HUANG Ming-ke 2002, 19(6): 488-492.  Abstract ( )   PDF (229KB) ( )   An approach of exact controllability combined with non-overlapping domain decomposition associated to the physical layer structure of air and coated material media is presented for simulations of the scattering of planar waves in 2-D coated aerodynamic shapes.Domain decomposition with non-matching finite element meshes at the interface is introduced,which allows to use different numbers of grid points required by different media.The conditions of compatibility at the interfaces between each subdomain are satisfied weakly by a Lagrange multiplier technique.The whole structure of the algorithm includes one outer loop for capturing time periodic solutions based on exact controllability and one inner loop for domain decomposed solutions through a treatment of Lagrange multiplier.Numerical results of the scattered fields are presented and compared for both perfectly conducting and coated aerodynamic shapes like 2-D airfoils,which reveal the effect of the coated layer.

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GENERATION METHOD OF UNSTRUCTURED ADAPTIVE 2-D MESHES FOR SIMULATING FLOWS WITH MOVING BODIES GENG Ji-hui, WU De-hong, WU Hui-zhong 2002, 19(6): 493-500.  Abstract ( )   PDF (492KB) ( )   A method to generate unstructured adaptive 2-D meshes is presented for simulating flows with moving bodies. Delaunay triangulation criterion in conjunction with the automatic point creation is used to generate 2-D unstructured grids. A local grid regeneration method is proposed to cope with moving boundaries. Numerical examples include a flow field induced by a moving circle plate, the interactions of shock waves with movable bodies and the movement of a projectile within a ram accelerator, illustrating an efficient and robust mesh generation method developed in the paper.

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ANALYSIS FOR THE EFFECTS OF REENTRY WAKE TURBULENCE ON RADAR CROSS SECTION YU Ming, NIU Jia-yu 2002, 19(6): 501-506.  Abstract ( )   PDF (281KB) ( )   By discussing the mechanism of turbulence plasma scattering electromagnetic wave in hypersonic reentry wake, the first order distorted wave Born approximation model about the radar cross section is derived from the underdense turbulence plasma for engineering application. Applicability to fully-developed turbulence wake plasma field is analyzed, the program about 3-D wake plasma is improved and compiled. Based on the flow field parameters about the turbulent wake and this scattering model, the effects of reentry wake turbulent plasma is analyzed on the radar cross section. Several representative factors chosen to examine are turbulence modeling, turbulent transition course, turbulent scale and the initial condition for the fluctuation intensity of electron concentration. The conclusions drawn is that turbulent transition course and scale are not too important, the initial condition for fluctuation intensity of electron concentration is very important, and turbulence modeling plays a little role under the specific conditions.

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NUMERICAL CHARACTERISTICS OF ULTRASONIC VELOCITY AND NONLINEAR ACOUSTIC PARAMETER B/A IN MIXTURES MADE UP OF MULTI-KINDS OF ORGANIC LIQUIDS YAN Xiang-hong, ZHANG Ya-ping 2002, 19(6): 507-511.  Abstract ( )   PDF (431KB) ( )   According to the Jacobson's Molecular Free Length Theory in liquids and the relationship between the ultrasonic velocity and the molecular free length in organic liquids, a relationship between the parameter of every component of the mixture and the nonlinear acoustic parameter B/A and the characteristics of the ultrasonic velocity in the mixtures made up of multi kinds of organic liquids is derived. When the parameter of every component (the density, the ultrasonic velocity, the free length, the isothermal compressibility coefficient, the isotonic expandibility coefficient、the nonlinear acoustic parameter B/A, ect.) is given, the characteristics of the ultrasonic velocity and the nonlinear acoustic parameter B/A of the mixtures can be calculated. The calculated results are in agreement with the experimental results.

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TWO-DIMENSIONAL STEADY INVERSE HEAT CONDUCTION PROBLEM QIAN Wei-qi, CAI Jin-shi, REN Bin 2002, 19(6): 512-516.  Abstract ( )   PDF (302KB) ( )   Based on the successful numerical simulation of the two-dimensional steady heat conduction problem with the Finite Control Volume method (FCV),two methods to solve the two-dimensional steady Inverse Heat Conduction Problem (IHCP),namely,the Sensitivity Method (SM) and the Adjoint Equation Method (AEM),are introduced.After the SM and the AEM are applied to a typical boundary condition inversion problem in a circular domain and the influence of the measurement noise to the inversion accuracy is analyzed,it is shown that both the SM and the AEM are feasible and effective to deal with the two-dimensional steady IHCP.

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EFFECTS OF SCATTERING PHASE FUNCTIONS ON THE RADIATIVE HEAT TRANSFER IN PLANE-PARALLEL MEDIA RUAN Li-ming, HAO Jin-bo, TAN He-ping 2002, 19(6): 517-520.  Abstract ( )   PDF (174KB) ( )   The finite-volume method for the radiative heat transfer is applied to linearly anisotropic plane-parallel scattering media.The results are compared with those obtained by the existing exact solutions,the radiation element method and the Monte Carlo method.It is shown that the results obtained by the finite-volume method are reliable.According to the analysis,the effect of the phase functions on the radiative heat transfer has some definite regularity.Furthermore,it is found that the ratio of the dimensionless heat flux in two two-dimension slabs with different scattering phase functions is a monotonous function of the optical thickness.It can be used as a benchmark to verify the results obtained with other methods.

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INTELLIGENT COMPUTER-AIDED DESIGN OF ZOOM LENS LAYOUT CHENG Xue-min, WANG Guang-yu, ZHANG Li-qin, WANG Yong-tian, WANG Qi 2002, 19(6): 521-526.  Abstract ( )   PDF (282KB) ( )   An expert system is developed for the automatic determination of zoom lens layout. Its features include the calculation of Gaussian parameters for different zoom mechanisms, and the selection and optimization of each lens group in a zoom system.

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EFFECTS OF DIRECT CURRENT ON ELECTROMAGNETIC PURIFICATION FOR LIQUID METALS ZHANG Bang-wen, REN Zhong-ming, DENG Kang, ZHONG Yun-bo 2002, 19(6): 527-531.  Abstract ( )   PDF (211KB) ( )   Based on the induced magnetic field of the conducted melt in a rectangular pipe,the 2-dimensional flow field is computed,then the inclusion trajectories are obtained by solving the MHD equations and the particle trajectory equations,respectively.Results show that the induced magnetic field is apt to produce convection in a square pipe,and thus to disturb the inclusion migration.To avoid it,the pipe with rectangular or circular cross section is better to be applied than one with square cross section for the electromagnetic purification.On the other hand,the induced magnetic field has an in built tendency of self limit,which makes it possible to remove inclusion from liquid melts only with currents (DC or AC) rather than with extra magnetic fields.

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A CLASS OF ALTERNATING GROUP METHOD OF FOUR POINTS FOR SOLVING DIFFUSION EQUATIONS WANG Wen-qia, JIN Cong-ming 2002, 19(6): 532-536.  Abstract ( )   PDF (179KB) ( )   A class of alternating group method of four points for solving diffusion equation is presented here. The method is unconditionally stable and has the obvious property of parallelism. This method can be used directly on parallel computers. Numerical experiments show that the method has high accuracy.

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MODELING 3-D ELECTROMAGNETIC RESPONSES OF THE MAGNETIC DIPOLE IN FREQUENCY DOMAIN BY USING THE EDGE FINITE ELEMENT METHOD SHEN Jin-song 2002, 19(6): 537-543.  Abstract ( )   PDF (294KB) ( )   The finite element formulation of the Maxwell equation is derived by using the edge finite element method and is used to simulate the 3-D electromagnetic responses to the subspace medium.Through the definition of the electric field in the edge of each cell,the problem of the discontinuity of the tangential components of the electric field between different cells in node finite element method is solved and this method also keeps the property of the non-divergence and finite rotation.The separation of the total electric field into the background and the secondary fields makes it possible that the technique proposed in the paper is suitable for the magnetic dipole in any direction.The properties of the convergence of seven Krylov subspace iterative solvers and the effectiveness of the incomplete Cholesky decomposition pre-conditioner are analyzed through two simulation examples.Comparisons of different solvers show that the generalized productive bi-conjugate gradient iterative solver processed with pre-conditioner has the best convergence and it is the best selection in 3-D electromagnetic modeling.

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INVERSION OF PARAMETERS IN 2-D ELASTIC WAVE EQUATION USING EVOLUTION STRATEGY ALGORITHM SUN Wei-zhi, HAN Hua 2002, 19(6): 544-548.  Abstract ( )   PDF (209KB) ( )   According to the principle that the computed response and the measured response should be fitted,the parameter inverse problem of 2-D elastic wave equation is reduced to an optimal problem of nonlinear multimode functions.The evolution strategy algorithm is used to search the global optimal solution and the inverse results are compared with those using genetic algorithm.Numerical simulations show that inversion accuracy obtained using evolution strategy algorithm is much higher than that obtained using genetic algorithm.The evolution strategy algorithm is an excellent nonlinear inversion method.

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SAGD NUMERICAL SIMULATION WITH HORIZONTAL WELLS WU Xiang-hong, YE Ji-gen, MA Yuan-le 2002, 19(6): 549-552.  Abstract ( )   PDF (293KB) ( )   An integrated SAGD numerical simulation model is described by combining the modules of the newly developed 1D multi-phase flow in horizontal wellbores with the steam flooding numerical simulation model. The behavior of steam chamber is calculated with the simulator and the results show that the simulator is effective for the SAGD simulation with horizontal wells. Several important factors influencing the size and the shape of the steam chamber are analyzed for the needs of practical SAGD designs.

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ONE DIMENSIONAL ADAPTIVE GRID TECHNIQUE WITHOUT ITERATION AND ITS APPLICATION TO BURGERS EQUATION KANG Hong-wen, LIU Chong-jian, XU Xiang-de 2002, 19(6): 553-556.  Abstract ( )   PDF (255KB) ( )   A new adaptive grid technique is proposed, which can redistribute grid points according to the equivalence of area under the curve of the weight function. So the iteration in the traditional technique through a variational approach is unnecessary here, and the efficiency is improved greatly. The new technique is applied to Burgers equation with analytic solutions. The results show that different weight functions have different distribution of grid points, and variational weight functions with time have variational distribution of grid points. Because the new technique can redistribute more grid points in the high gradient solution regions in response to the numerical solution, it can capture the shock efficiently.

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TWO-DIMENSIONAL ADAPTIVE QUAD/CARTESIAN HYBRID GRID SOLVER FOR EULER AND N-S EQUATIONS SANG Wei-min, LI Feng-wei, E Qin 2002, 19(6): 557-560.  Abstract ( )   PDF (250KB) ( )   A method for the adaptive refinement of a Quad/Cartesian grid for the solutions of the Euler and N-S equations is presented.An adaptive Quad/Cartesian hybrid grid method,which retains the advantages of the Cartesian grid approach and, at the same time, touches the viscous flow problems,is provided.The body fitted Quad grids are generated around the body and the Cartesian grids are used in the remains of the flow field.The flow solver of the Euler and N-S equations is performed by a conventional algorithm,including the finite volume method and the Runge-Kutta time-stepping scheme.The grid adaptation and the flow solver achieve reasonable efficiency and accuracy with minimum computer resources.Based on the above approach,the numerical analysis of flows around the single-element and the multi element airfoils is given.The numerical results presented show the flexibility of this approach and the accuracy attainable by the solution-based refinement.