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25 January 2005, Volume 22 Issue 1 Previous Issue    Next Issue

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A Quasi-local Vibration Algorithm for Damped Stochastic Differential Equations SONG Yan-li, BAO Jing-dong 2005, 22(1): 1-6.  Abstract ( )   PDF (251KB) ( )   A quasi-local vibration algorithm is proposed to simulate the damped stochastic differential equations.Using the potential Taylor expansion and the operator splitting technique,the time evolution operator of a dissipative particle is factorized into two parts: an operator which describes the deterministic path of the system and a diffusion operator which incorporates fluctuation away from path.The differential equation corresponding to the fluctuation process is solved analytically, and the deterministic trajectory equation is calculated with the Euler algorithm.Compared with other algorithms, it is shown that the calculated results by the present algorithm are more stable and converge to the correct value when the time step is large.

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Adaptive Coordinate Transformation Methods YUAN Guang-wei, SHEN Long-jun, SHEN Zhi-jun 2005, 22(1): 7-12.  Abstract ( )   PDF (248KB) ( )   A series of adaptive corrdinate transformation methods are proposed in which the grid angles are preserved approximately,and the material interface is kept to be Lagrangian description and a minimum difference (in the least-squares sense) between the mesh velocity and the fluid velocity is achieved.The new coordinate system is adapted to important features of flow fields.

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A High Order Accurate TVD Difference Scheme for Hyperbolic Conservation Laws ZHENG Hua-sheng, ZHAO Ning 2005, 22(1): 13-18.  Abstract ( )   PDF (242KB) ( )   A high-order,high resolution,conservative TVD difference scheme is presented for one dimensional hyperbolic conservation equations.The basic idea is as follows.Firstly,the computation domain is divided into many non-overlapping subdomains,and then each subdomain is further subdivided into small cells according to the required accuracy; Secondly,by the flow direction,flux splitting is introduced,and high-order approximation in the subdomain are used to compute the positive/negative numerical fluxes at cell boundaries.Furthermore,TVD corrections are considered to prevent oscillations near discontinuities from the high-order interpolation.Moreover,by means of high-order TVD Runge-Kutta time discretization,a high-order fully discretization method is obtained.The extension to one dimensional systems is also carried out.Finally,numerical experiments on one dimensional Euler equations are given,and numerical results are satisfactory.

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Alternating Segment Difference Schemes for Dispersive Equations with Diffusion WANG Wen-qia, FU Shu-jun 2005, 22(1): 19-26.  Abstract ( )   PDF (295KB) ( )   New asymmetric difference schemes for dispersive equations with diffusion are given. A parallel alternating segment difference scheme for solving the equation is constructed, which is unconditionally stable, and can be used directly on parallel computers. Numerical experiments for the model problem are performed, and the results are reported.

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Parallel Numerical Simulation and Analysis of Migration-Accumulation of Oil Resources YUAN Yi-rang, DU Ning, HAN Yu-ji, FENG Guo-xiang, YANG Cheng-shun, ZUO Dong-hua 2005, 22(1): 27-37.  Abstract ( )   PDF (572KB) ( )   Parallel numerical simulation of migration-accumulation of oil resources in porous media is to describe the process of oil migration and accumulation in basin evolution.It is of great value to the evaluation of oil resources and to the determination of the location and amount of oil deposite.This paper puts forward a numerical model,a parallel operator splitting-up implicit iterative scheme,parallel arithmetic program,parallel arithmetic information and alternating-direction mesh subdivision.It also discusses computation and analysis of different mesh step lengths.For the actual situation of Tanhai region of Shengli Petroleum Field,the numerical simulation test results and the actual conditions are coincident.For the model problem (nonlinear coupled system) optimal order estimates in l2 norm are derived to determine the errors.The problem in the fields of permeation fluid mechanics and petroleus geology appears to be solved.

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Analysis of Ion Bombardment in Si-FEA GAO Ying-bin, ZHANG Xiao-bing, LEI Wei, WANG Bao-ping 2005, 22(1): 38-42.  Abstract ( )   PDF (348KB) ( )   Ion bombardment affects the stability and lifetime of micro-tip field emission devices. In the Si field emission array (FEA), the atoms in the residual gas may collide with electrons and be ionized, so many ions could be produced. Due to the electrical field in the FEA device, the ions bombard on the Si tips. This paper analyzes the mechanism of ion bombardment on the Si tip. The process concerning ion generation and ion bombardment is numerically simulated. The damage to the tip is analyzed quantitatively, and related conclusions are given.

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A Meshless Method Based on Coupled Radial and Polynomial Basis Functions ZENG Qing-hong, LU De-tang 2005, 22(1): 43-50.  Abstract ( )   PDF (371KB) ( )   A new approximate method based on coupled radial basis functions and polynomial basis functions is presented.Only nodes information is needed when this method is used for interpolation over a set of discrete nodes,the background mesh is totally unnecessary.The establishment,properties,interpolation behaviors of approximate functions,the shape functions and their derivatives are described in detail.The modified variation principle and partition of unity quadrature are employed with coupled approximate function to solve boundary value problems. Numerical examples show excellent agreement with exact solutions.

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The Electronic Structure of Quasi-one-dimensional DisorderedSystems with Three Parallel Chains SONG Zhao-quan, XU Hui, LIU Xiao-liang, MA Song-shan 2005, 22(1): 51-55.  Abstract ( )   PDF (259KB) ( )   The densities of electronic states (DOS) of quasi-one-dimensional disordered systems with three parallel chains are computed with thirty thousand sites based on the negative eigenvalue theory. Compared with one-dimensional and quasi-one-dimensional disordered systems under conditions as diagonal disordered system and non-diagonal disordered system, the electronic structure, the localization of electrons, the distribution of the system energy and the dimensional effects are discussed. The results show that the diagonal disorder causes increasing of the number of localized electrons, and the non-diagonal disorder leads to changing of the distribution of the system energy. Comparing the electronic structure of one-dimensional system and quasi-one-dimensional system with three chains, we find that the peak number of the DOS increase, and the bandgap energy of zero DOS decreases.The dimensional effect of system under the same condition is shown.

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A Conjugate Gradient Method for Inverse Heat Conduction Problems with Multi-variables in Transient-state XUE Qi-wen, YANG Hai-tian, HU Guo-jun 2005, 22(1): 56-60.  Abstract ( )   PDF (265KB) ( )   A general numerical model is presented to identify multi_variables,including thermal parameters and boundary conditions for inverse heat conduction problems in transient state.Sensitivity formulas are derived.A conjugate gradient technique is employed.The effects of the number of sample points,the data noise and initial guess on solutions are given.A numerical calculation is performed and discussed.

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A Large Eddy Simulation of Isotropic Turbulence Decay XIA Jian, LIU Feng 2005, 22(1): 61-64.  Abstract ( )   PDF (206KB) ( )   A compressible large eddy simulation (LES) technique based on a highly efficient and well validated finite volume,multigrid driven method is developed.The Jameson's central scheme with second and fourth order artificial dissipation is used for space discretization and dual time methodology is implemented for time marching.The subgrid scale stress tensor and the subgrid scale heat flux are simulated with Smagorinsky model.A typical simulation of isotropic turbulence decay is performed to verify the accuracy and efficiency of this method.The simulated time evolution of energy spectra and decay of the resolved turbulence kinetic energy are in good agreement with the filtered experimental CBC data.

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Radar Cross Sections of Airplane Wings in the 2D FDTD Method XUE Xiao-chun, WANG Xue-hua 2005, 22(1): 65-69.  Abstract ( )   PDF (262KB) ( )   Bistatic radar cross sections (RCS) of NACA0012 and a square-pole of metal are computed with 2D FDTD program. Numerical results are consistent with those of literature available. Hence the 2D FDTD program is shown correct and effective. Calculations are performed for the bistatic RCS of 2D wings, sweepback-wings and triangle-wings. These results show that wings with different figure have different profiles of RCS and varying angle χ causes the change of sweepback-wing' and triangle-wing's RCS. The requirement of reducing RCS could be reached through choosing different figure of wing or varying χ according to the design demand.

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Effects of Carbon Nanotube Structure and Size on Hydrogen Physisorption CHENG Jin-rong, YUAN Xing-hong, ZHAO Min, HUANG De-cai, ZHAO Li, ZHANG Li-bo 2005, 22(1): 70-76.  Abstract ( )   PDF (472KB) ( )   Grand canonical Monte Carlo (GCMC) method is adopted to investigate the dependence of hydrogen storage capacity on the diameter of a single-walled carbon nanotube (SWCNT), the distance between walls and the shell number of a multi-walled carbon nanotube (MWCNT),as well as the inter-tube distance and configuration of SWCNT array (SWCNTA),at 298K and 10MPa.The calculated results show that when the diameter of SWCNT approaches 6 nm the average number density (nAV) of hydrogen within the tube reaches its maximum.When the difference between the internal radius and the external radius increases from 0.34 to 0.61 or 0.88 nm the hydrogen storage capacity is improved effectively.As the inter-tube distance of SWCNTA approaches 1.7 nm nAV within the interstitial space of SWCNTA reaches its maximum and a square array is better than a triangular array for hydrogen physisorption.It is also found that nAV within the interstitial space is larger than that within the tube whether for a square array or a triangular array,only if inter-tube distance is larger than 0.6 nm.The hydrogen storage capacity could be effciently increased by the reasonable choice of the diameter of SWCNT,the distance between walls of MWCNT,the inter-tube distance and configuration of SWCNTA.Conclusions are discussed and explained.

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Numerical Simulation of Coupled Heat Transfer in HiTAC Furnace WANG Li-jun, LI Ai-min, LI Ji-huai, HAO Yu-ling, ZOU Zong-shu, CAI Jiu-ju 2005, 22(1): 77-82.  Abstract ( )   PDF (511KB) ( )   A three-dimensional numerical simulation of the temperature field in high temperature combustion furnace is performed using a method of discrete ordinate to solve the radiation transfer and transfer coupled equations.A computer program of flow, combustion, heat transfer and NOx turbulent formation is developed. The temperature distribution of Fuel Direct Injection (FDI) is numerically analyzed at different preheated air temperature and the validity of the applied numerical simulation is tested. The simulation results show that when preheated air temperature increases the maximum temperature gets larger, the temperature gradient becomes lower and the flame length longer.They are in agreement with experiments.

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Numerical Simulation of Fluid Flow and Heat Transfer in a Plasma Sprayer WANG Wei-ming, WANG Bao-hua, LI Da-yong, PENG Ying-hong, ZHANG Yi-shun 2005, 22(1): 83-87.  Abstract ( )   PDF (497KB) ( )   Based on CFD and heat transfer theory,a model of the nozzle in a plasma sprayer is developed.The flow and heat transfer of the cooling water are simulated with coupling.It is found that the wall near heat source and the gasket in the back of the nozzle are the most deficient cooling parts.Then different parameters of cooling water are analyzed,and the optimum velocity and direction of cooling water are found.

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An Iterative Regularization Method for the Space Charge Distribution in Dielectrics HU Luo-quan, ZHENG Fei-hu, ZHANG Ye-wen 2005, 22(1): 88-93.  Abstract ( )   PDF (342KB) ( )   The application of iterative regularization deconvolution to solve an ill-posed problem is discussed. Firstly, the theoretical foundation of iterative regularization is introduced, and a new Fredholm integral equation of the first kind including space charge distribution is derived .The effect of additive Gaussian white noise for iterative deconvolution algorithm, and the effect of iterative convergence criterion for the numerical solution are studied, respectively. It is shown that the solution of ill-posed problems could be obtained with iterative deconvolution algorithm under lower level noise circumstance. It also indicates that the precision of numerical solution is influenced by the iterative convergence criterion. Finally,the original experimental data are dealt with and the real space charge distribution in dielectrics is obtained.