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25 May 2003, Volume 20 Issue 3 Previous Issue    Next Issue

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Numerical Method for Volume Vaporization Model of Laser-target Interaction TAO Ying-xue, GUAN Ji-li, CHEN Fa-liang 2003, 20(3): 189-192.  Abstract ( )   PDF (206KB) ( )   With the phase change in laser ablation process being described by Clausius-Clapeyron equation,by means of von-Neumann difference scheme,a volume vaporization model of laser-induced target vaporization process is proposed and numerically solved,which can effectively describe the occurrence and evolution of LSD waves.The fact that results predicted by the model compare well with those from an interface vaporization model previously addressed by the authors validates the availability of the volume vaporization model and the von-Neumann difference scheme in solving the hydrokinetics process of laser-induced target vaporization.This model provides a more convenient way for computing a two-or three-dimensional process.

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Adaptive Nonuniform Grid Upscaling Method of Three-dimensional Transient Heterogeneous Fluids in Porous Media YANG Quan-yi, LIU Fu-ping, YANG Chang-chun, LIU Li-feng, ZHUO Lei 2003, 20(3): 193-198.  Abstract ( )   PDF (378KB) ( )   Adaptive grid technology is applied to upscaling method of 3D fluid equations in porous media. Where the permeability or porosity change is abnormal, the fine grid blocks are automatically adopted and the 3D fluid equations in porous media is solved by the direct method. In the other regions, the nonuniform upscaling method is adopted, i.e., using fine grid blocks in the high flow regions of the model. Using this method, the pressure distribution of the 3D transient heterogeneous fluid in porous media is calculated. Results show that the solutions by using nonuniform adaptive upscaling method of 3D transient heterogeneous fluid in porous media very approach the solutions by using fine grid blocks in the regions the permeability or porosity is abnormal and very approach the solutions by using coarse grid blocks in the other regions; however, the computation speed by using adaptive upscaling method is 100 times more than that by using fine grid block method.

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Analytic Solution of the Diffusional Release of Solute from a Non-erodible Polymeric Matrix S. Wasuwanich, N. Jinuntuya, P. Petpirom 2003, 20(3): 199-204.  Abstract ( )   PDF (371KB) ( )   This work presents a systematic framework to achieve the desired diffusional release of drug from a non-erodible polymeric matrix.The model of this representation is a boundary value problem based on Fick's second law.The solution of this governing equation is divided into two phases.Phase I is a Stefan problem with a moving diffusion front while Phase Ⅱ begins after the moving diffusion front has disappeared. The main objective of the present study is to investigate analytically the complete release process of a solute from a non-erodible matrix up to a time corresponding to the absence of the diffusion front.This solution may serve as a basis for modeling more complicated systems.

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Difference Scheme by Integral Interpolation Method for Three Dimensional Diffusion Equation CHEN Guang-nan, LI De-yuan, WAN Zheng-su 2003, 20(3): 205-209.  Abstract ( )   PDF (248KB) ( )   Numerical simulation for three-dimensional diffusion equation is studied. Using integral interpolation method, the difference scheme on the irregular hexahedral grid is constructed which consists of 27 neighboring grids and is available for solving quasi-linear diffusion equation with discontinuous coefficients on distortion mesh. Flow flux through interfaces and temperature on the nodes are deduced and numerical test is given.

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Molecular Field Theory of the Homogeneous-to-homeotropic Alignment Transition for a Nematic Phase XIANG Lan, ZHANG Zhi-dong 2003, 20(3): 210-214.  Abstract ( )   PDF (328KB) ( )   The molecular field theory is used to invesigate the behaviour of the nematic alignment transition within nematic liquid crystal (NLC) films confined by two rubbed substrates. The molecular centres of mass are located at the sites of a simple cubic lattice. The NLC consists of polar molecules and the molecules of the first layer of the NLC adjacent to the soild bounding surface are affected by both surface dispersion and polar forces. From self-consistent numerical calculations, three types of phase diagram are obtained, which exhibit a transition from a high temperature homogeneous alignment to a low temperature homeotropic alignment. The parameter ranges of two surface interaction which leads to the homogeneous-to-homeotropic alignment transition is obtained. The results show that the surface dispersion action, not the surface polar one, can be changed by the grating of the substrate and the surface polar interaction can give rise to the homogeneous-to-homeotropic alignment transition.

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Short Range Correlations Between Molecules in Cholesteric Phase of Liquid Crystals ZHANG Zhi-dong, LU Zun-ming 2003, 20(3): 215-218.  Abstract ( )   PDF (208KB) ( )   The two-particle cluster theory of nematic liquid crystals is generalized to study a two-dimensional model of cholesteric phase. The chiral molecules are placed at the sites of a three-dimensional simple cubic lattice with molecular orientations confined to two dimensions. The theoretical result shows that the helical wave-vector for equilibrium state depends on temperature and the cholesteric-isotropic phase transition exists. The two-particle cluster theory, taking into accout short-range correlations between molecules, yields numerical results which are closer to those of the Monte Carlo simulation than the mean field theory.

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Simulation of Interaction of Shocks with a Cylinder Interface by Means of Ghost Fluid Method CHENG Jun-bo, TANG Wei-jun, LI De-yuan, FU De-xun 2003, 20(3): 219-225.  Abstract ( )   PDF (510KB) ( )   Two-dimensional compressible flow field for the interaction of shocks with cylinder interface is directly simulated by using Ghost Fluid method (Ghost) and γ-model method, respectively, with the same discrete order in space and time. Numerical results are compared with the experimental results. They are almost alike in the beginning time and show the right position of interface, right strength and velocity of shocks. With the time developing, the effect of large numerical dissipation of γ-model method becomes greater and greater while the low numerical dissipation of Ghost method makes it efficient to simulate the moving interface well. Comparison with experiments proves that Ghost method is better than γ-model method in simulating the problem of interface instability.

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Flow Characteristics of Flaps with Slots in Boundary Layers ZHANG Pan-feng, WANG Jin-jun 2003, 20(3): 226-232.  Abstract ( )   PDF (421KB) ( )   The flow characteristics of various flaps with slots is studied by solving the Reynolds averaged Navier-Stokes equations with two-layer zonal model,while the pressure distribution is measured by experiments.The results reveal that the flow structure of flaps with slots depends on the interaction of flows around two parts of the flaps with slots.The two flows have no intervention at porosity η=50%;but they interact stronly at η=20%,30%.The circulation zone downstream of the flaps becomes larger and has weaker turbulent intensity.

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Optimization Design of Transonic Wings with Drag Reduction and Constant Lift Coefficients YANG Xu-dong, QIAO Zhi-de, ZHU Bing 2003, 20(3): 233-238.  Abstract ( )   PDF (310KB) ( )   It is interesting for designer how to reduce drag of transonic wing which meets design lift requirement. Based on adjoint equation theory and using Euler equations, an optimization design method of transonic wing with drag reduction and constant lift coefficient is developed. According to the cost function given, three dimensional adjoint equations and their boundary conditions in physical space are dreived, and a numerical method is developed to solve the three dimensional adjoint equations. The sensitivity derivation of objective function with respect to design variables can be obtained by using grid perturbation method, and the quasi-Newtonian algorithms are used. Some numerical tests are made for the drag reduction with constant lift coefficient. The test results show that shock strength on wing surface will become much weaker than that of initial wing, thus drag may be reduced effectively.

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Numerical Simulation of Polymer Flooding with Dispersion and Adsorption HOU Jian, LI Zheng-quan, WANG Yu-dou, CHEN Yue-ming 2003, 20(3): 239-244.  Abstract ( )   PDF (356KB) ( )   By using explicit saturation and implicit concentration methods,numerical solution is presented to the polymer drive model characterizing dispersion and adsorption of polymer solution flowing through a porous medium.Saturation equation is solved by using an explicit total variation diminishing(TVD)method.To ensure the stability of concentration equation calculation,Crank-Nicolson difference format is used in spatial discretization,and variable is quasi-linear disposed in temporal discretization.The validity of the method presented is verified by comparison with analytic solutions.The calculated example indicates that dispersion causes dilution and dissipation of polymer solutions,and adsorption results in a loss,thus leading to lagging of concentration propagation.Also,the important polymer flooding mechanism- "oil block" is illustrated in the results of calculation.Under the condition of slug injection,the breakthrough time of oil enrichment zone lies between the breakthrough time of polymer concentration front and polymer concentration peak.

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Application of Two Dimensional Wavelet Transform in the Reconstruction of Tibetan Plateau Topography DAI Xin-gang, WANG Guo-jun, WANG Ping 2003, 20(3): 245-254.  Abstract ( )   PDF (845KB) ( )   A single pulse and peak signals are decomposed and reconstructed with four types of wavelet bases in different orders. Results demonstrate that the biorthogonal wavelet is of a best fitting to the signals, and the Coifman wavelet is at the last in the four bases. After truncating the expansion series of the wavelets and the Fourier transform, the reconstruction shows that the wavelet reconstruction got higher precision with less number of non-zero coefficients and the local error distribution compared with the Fast Fourier transform we calculated. Thus the wavelet reconstruction can greatly attenuate "Gibbs phenomenon" and limit the errors in a narrow domain around the singularities of the signals.Besides, we also make expansions for the topography of Tibetan plateau in wavelets and Fourier transform. Its reconstruction with or without truncation shows the similar features as the one-dimensional signal reconstruction above.

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Computer Simulations of Hydrogen Storage in Single-walled Carbon Nanotubes CHENG Jin-rong, YAN Hong, CHEN Yu, ZHANG Li-bo, ZHAO Li, HUANG De-cai, TANG Rui-hua 2003, 20(3): 255-258.  Abstract ( )   PDF (191KB) ( )   The capability of hydrogen storage in zigzag single-walled carbon nanotubes is investigated.Relations of diameter and length with the hydrogen reserves and the distribution of hydrogen storage in single-walled carbon nanotubes are obtained.A new expression of hydrogen storage capability is presented.

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Parameter Inversion from Iterative Solution of High-order Scattering of Vector Radiative Transfer for One Layer of Random Non-spherical Particles LIANG Zi-chang, JIN Ya-qiu 2003, 20(3): 259-263.  Abstract ( )   PDF (322KB) ( )   Employing the first-order Mueller matrix solution of vector radiative transfer equation for one layer of small random spheroids, simulated measurements of high-order co-polarized and cross-polarized backscattering are obtained. Iterative inversion of the dielectric constant of small spheroids and the number of particles per unit area is developed. The inversion from simulated and real AirSAR data and its dependencies upon the parameters and the random noise are discussed.

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Solving Eu-151 Mössbauer Spectra with Genetic Algorithm SUN Xue-feng, LIN Jun, HUANG Hong-bo, Ali, HE Yun, DAI Yao-dong, HSIA Yuan-fu 2003, 20(3): 264-266.  Abstract ( )   PDF (195KB) ( )   Genetic Algorithm(GA) is provided to solve the Eu2O3(Cubic) Mössbauer Spectra. And the results are compared with parameters coming from references and MossWin(another software for solving Mössbauer Spectrum.

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Discussion on the Choice of the Fourier Transformation Form in Numerical Solutions of Nonlinear Schrödinger Equation ZHANG Xiao-guang, YANG Bo-jun, YU Zhong-yuan 2003, 20(3): 267-272.  Abstract ( )   PDF (515KB) ( )   Relationships between the choice of the positive and negative frequency expression of optical waves, adoption of Fourier transformation form and form of nonlinear Schrödinger equation are discussed. The generally accepted form of nonlinear Schrödinger equation is the result of choosing the negative frequency expression. In accord with the negative frequency expression, the form of Fourier transformation cannot be chosen at will. When the nonlinear Schrödinger equation is solved using numerical methods based on Fourier transformation, the form of fast Fourier transformation must be paid attention in the programming languages used. In most programming languages, the adopted forms of fast Fourier transformation and inverse transformation are opposite to the forms adopted in nonlinear optics. It is also pointed out that some related numerical errors existed in some references.

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Turbulent Flow Calculation Using B-B One Equation Turbulence Model on Unstructured Meshes CHENG Juan, HUANG Ming-ke 2003, 20(3): 273-278.  Abstract ( )   PDF (403KB) ( )   How to calculate turbulent flow by solving Navier-Stokes equations on unstructured grids is investigated.The cell-center finite volume method is used to solve N-S equations.Baldwin-Barth one equation turbulence model is chosen to calculate turbulent flow which is especially suitable to unstructured meshes.The model consists of a single advection-diffusion equation with a source term.In order to solve this model equation on irregular grids,an explicit finite-volume scheme is delivered,and its time step limiting condition is obtained by analyzing stability of the scheme which possesses a source term.At the end,the numerical examples,such as turbulent flow around flat,RAE-2822 foil and multi-element foil,are given which verify the validation of the computational method.

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Methods to Calculate the Energy Spectra in the Program MEND CAI Chong-hai 2003, 20(3): 279-282.  Abstract ( )   PDF (264KB) ( )   The methods to calculate the energy spectra of all kinds of emitting light particles and recoil nuclei for multi-level particle emission in medium energy region(≤250MeV),comparison of the efficiency between this method and the traditional one and two calculated examples are given.