Archive

25 May 2008, Volume 25 Issue 3 Previous Issue    Next Issue

---

For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Select

Application Analysis on Dual-time Stepping ZHAO Huiyong, LE Jialing 2008, 25(3): 253-258.  Abstract ( )   PDF (286KB) ( )   The stability, starting problem, initial value of sub-iteration and convergence criterion of implicit iteration of the dual-time stepping method are studied. Analysis of von Neumann stability indicates that in the implicit method employed in sub-iteration real time step is limited by the requirment of stability. Computation on Sod's shock tube validates the conclusion.

Select

Merging of Vortex Pair at Different Separating Distances DANG Huixue, CHEN Zhimin, YANG Zhichun 2008, 25(3): 259-262.  Abstract ( )   PDF (344KB) ( )   To study nonlinear aerodynamics of merging vortex pair, a simplified model is employed to obtain merging at different separating distances by solving N-S equations in an LES turbulence model. Interactions of vortex merging, effects of separation distance on merging and control of vortex position by merging of vortex pair with different vortex strength ratios are analyzed with topological structure of streamlines. It is shown that merging distance increases nonlinearly with separating distance. Increasing separation distance decreases ability to control vortex position.

Select

Multi-step High-order Finite Difference Schemes for Time Domain Maxwell's Equations HUANG Zhixiang, SHA Wei, WU Xianliang, CHEN Mingsheng 2008, 25(3): 263-268.  Abstract ( )   PDF (274KB) ( )   Multi-step high-order finite difference schemes for infinite dimensional Hamiltonian systems with split operators are proposed to solve time domain Maxwell's equations. Maxwell's equations are discretized in time direction and in spatial direction with different order of sympleetie schemes and fourth-order finite difference approximations, respectively. Stability analysis and numerical results are presented. A five-stage fourth-order multi-step high-order finite difference scheme proves accurate and efficient, and applicable to long time simulations.

Select

Optimal Influence Radius of Weight Functions in Meshless Methods in Three Dimensions NIE Yufeng, MENG Zhuo, FAN Xiangkuo 2008, 25(3): 269-274.  Abstract ( )   PDF (311KB) ( )   We establish a practical mathematical model to compute optimal influence radius of weight functions in three dimensions. It is solved with linear basis and quadratic basis. Effects of error estimates, computing time and condition numbers of weight function with different influence radius on computation performance are investigated. Numerical examples demonstrate relability, efficiency and optimality of the influence radius.

Select

Two-dimensional Unstructured Mesh Generation with Vector Boundary Advancing WANG Shengxi, SONG Songhe, ZOU Zhengping 2008, 25(3): 275-283.  Abstract ( )   PDF (767KB) ( )   We present a method, vector boundary advancing method, to generate unstructured triangle meshes, and prove its feasibility. It lays out boundary points based on domain scales and generates background meshes with vector boundary advancing method. With sign-area function and probability filer, it obtains initial points in the domain. Spring-Laplace method and side-swapping method adjust location and structure of the mesh and prevent points from getting out of the domain. The method can do adaptive refine and derefine successfully and can deal with fixed-points, fixed-lines and inner-boundary. An efficient smooth adaptive triangulation divided in two-dimensional domain according to scales is realized.

Select

Modeling of HL-2A Tokamak Edge Plasma with Auxiliary Heating CHENG Fayin, LI Li, HOU Binglin 2008, 25(3): 284-288.  Abstract ( )   PDF (330KB) ( )   Edge region of HL-2A tokamak with closed divertor configuration is divided into meshes by a code combined with 2D fluid edge modeling code B2.5. Postprocessing code is provided. HL-2A tokamak edge plasma with about 3 MW auxiliary heating power is modeled and analyzed. It indicates that the plasma in front of divertor target plate exhibits high density and low temperature, and the divertor runs in conduction-limited regime, i.e, in high recycling mode.

Select

Fourier-Bessel Series Algorithm in Fractal Diffusion Model for Porous Material WANG Sheng, MA Zhengfei, YAO Huqing 2008, 25(3): 289-295.  Abstract ( )   PDF (457KB) ( )   Fourier trigonometric series algorithm used in Fick's diffusion law is extended to Fourier-Bessel algorithm in a fractal diffusion model for porous materials. It is applied to chemical engineering for computation of concentration distribution and relative adsorption. The fractal diffusion model introduces structure parameters df and θ Concentration distribution and relative adsorption calculated by fractal diffusion model are qualitatively consistent with those by Fick's diffusion law. df and θ exhibit different effects on concentration distribution of porous materials, and describe diffusion in porous materials well.

Select

Pressure of Triple Porosity Condensate Gas Reservoir with Variable Wellbore Storage ZHANG Yanyu, WU Xiaodong, NIE Fajian 2008, 25(3): 296-300.  Abstract ( )   PDF (233KB) ( )   In a condensate gas reservoir welhest model of Xu & Lee, error function express of wellbore phase redistribution is adopted and a mathematical model of variable wellbore storage in triple porosity condensate gas reservoir is shown. With Laplace transformation and Stehfest inversion, effects of pressure parameters on pressure and differential of pressure are analyzed. Typical pressure curves are given.

Select

Finite Element Method with Perfectly Matched Absorbing Layers for Wave Scattering from a Cavity ZHANG Deyue, MA Fuming, FANG Ming 2008, 25(3): 301-308.  Abstract ( )   PDF (338KB) ( )   A finite element method with perfectly matched layers(PML) is developed for wave scattering from a two-dimensional cavity embedded in an infinite ground plane. Based on a variational formulation it uses the PML technique to truncate an unbounded computational domain to a bounded one. Hence, a PML problem instead of the original scattering problem is solved. Convergence of the PML problem to the scattering problem is analyzed. Numerical experiments illustrate competitive behavior of the proposed method.

Select

3D FDFD Algorithm with TF/SF Technique for Electromagnetic Scattering from a Composite Target HU Xiaojuan, GE Debiao, WEI Bing 2008, 25(3): 309-314.  Abstract ( )   PDF (352KB) ( )   A total-field/scattered-field (TF/SF) technique is used to introduce an incident wave for a scattering problem in three-dimensional finite-difference frequency-domain (FDFD) method. According to the equivalence principle, an incident wave is introduced in total-field region by setting equivalent electromagnetic currents on TF/SF boundary. FDFD equations at nodes near TF/SF boundary are modified to satisfy conditions that all nodes involved belong either to total-field or to scattered-field. Numerical results validate this technique. The presented technique is mainly applied to scattering problem with a composite target,which is composed of perfectly electronic conductor (PEC) and lossy dielectric medium. Bistatic radar cross section (RCS) of a composite yon Karman missile warhead and a missile model are computed with FDFD method. The results demonstrate its applicability in analyzing electromagnetic scattering with composite targets.

Select

Monte Carlo Simulation of Nematic Droplets with Spatially Anisotropic Pair Potential ZHANG Yanjun, ZHANG Zhidong, Zhu Lizhi 2008, 25(3): 315-322.  Abstract ( )   PDF (440KB) ( )   Nematic droplets are studied with Monte Carlo simulation in a spatially anisotropic molecular pair potential model. The potential is based on a lattice model and dependent on elastic constants of liquid crystals. We assume that nematic droplet surface is a free surface and introduce tangent-introrse intensity to quantitatively describe intrinsic anchoring induced by surface. The tangent-introrse intensity and the second order parameters in different regions of droplets at low temperature are calculated by two schemes with spatially anisotropic potential and are compared with those in Lebwohl-Lasher model. Only one scheme can give intrinsic easy axis near droplets surface and introrse intensity is related to K33/K11. The degree of nematic order in the vicinity of droplet surface becomes lower from inner shell to outer shell due to incomplete anisotropic nematic-nematic interactions.

Select

Inversion of Particle Size Distribution from Dynamic Light Scattering Data with Gray-code Genetic Algorithm LI Shaoxin 2008, 25(3): 323-329.  Abstract ( )   PDF (422KB) ( )   A stochastic inverse technique based on Gray-code genetic algorithm (GGA) is proposed for inversion of particle size distribution from dynamic light scattering (DLS) data. It is shown that GGA inverts particle size precisely for different distribution with no random noise. GGA shows stability for distribution with random noise and gives distribution of main peaks. In numerical experiments of latex sphere, GGA inverts dynamic light scattering data with biomodal distribution successfully. Compared with standard genetic algorithm and inverse Monte Carlo method, GGA shows high efficiency in searching optimum results.

Select

D-FFT Calculation of Collins' Formula LI Junchang 2008, 25(3): 330-334.  Abstract ( )   PDF (256KB) ( )   Collins' formula and its inverse calculation are expressed in a convolution form. Corresponding transfer function is deduced. Sampling theory conditions in fast Fourier transform (FFT) to calculate Collins' formula are discussed. Diffraction field as optic wave passes through an optical system and reconstruction of incident plane are shown.

Select

Stable and Fast Algorithm for Identification of Source in Heat Conduction Problems XIAO Tingyan, ZHANG Junli 2008, 25(3): 335-343.  Abstract ( )   PDF (423KB) ( )   With properties of non-negative operator and Lax-Milgram theorem, we transform an ill-posed 1D heat conduction problem into a well-posed second kind Volterra equation, and introduce a stable and fast algorithm. Related theoretical analysis is shown. For the determination of regularization parameter, the algorithm employs two posterior strategies, which can be realized quickly whether the error level of input data are known or unknown. Numerical tests demonstrate merit of the algorithm.

Select

3rd Superharmonic Resonance of Current-carrying Conductor Subjected to Harmonic Excitation XI Xiaoyan, YANG Zhian 2008, 25(3): 344-348.  Abstract ( )   PDF (236KB) ( )   3rd superharmonic resonance of a current-carrying conductor subjected to harmonic excitation and ampere force is studied. Duffing equation of the system is established by means of dynamics theory. With a method of multiple scales for nonlinear vibrations, approximate solution of 3rd superharmonic resonance is obtained. Influence of director current, alternating current, detuning, tension and excitation on the system is analyzed.

Select

Nano Valve of Medicinal Carrier:A Molecular Dynamics Study CHEN Jong-shun, WANG Chin-shu, WANG Ying-chin 2008, 25(3): 349-357.  Abstract ( )   PDF (749KB) ( )   Mass and heat transfer between fluid molecules and a carbon tube is studied via molecular dynamic simulation with Lennard-Jones potential and Bernner-Tersoff potential. A valve hole of area 17.3~116.9Å2 is formed by removing different numbers of molecules from the flank of a (5,5) armchair carbon tube. The results indicate that diffusion behavior can not describe the phenomena completely, since the hydrogen atoms penetration rate Vb can also be affected by hole size at the same temperature. The Maxwell-Bohzmann energy distribution equation is modified. Atom release rate and valve hole size are interdependent. Variation of potential energy barrier, work function and energy gap at different valve sizes and influences on the dynamic behavior, such as flow rate and velocity by molecule penetration, are studied. The characteristic is used for design of nano-valve, particle separator or chemical reactor.

Select

Electronic Structure of Fibonacci Chains LIU Xiaoliang, XU Hui, LI Yanfeng, LI Mingjun 2008, 25(3): 358-364.  Abstract ( )   PDF (393KB) ( )   For a Fibonacci chain constructed recursively with Sm+1={Sm|Sm-1}, in a tight-binding model of single electron, we investigate numerically density of electronic states and electronic energy band structure with negative eigenvalue theory and three diagonally symmetric matrixes. Trifurcating structure of energy band of the system is demonstrated. With renormalization-group method and scattering theory, we study localization length and transmission coefficients of electronic states in a chain. At particular eigen-energies, extend states with localization lengths greater than size of the system are found and transmission coefficient is equal nearly to 1. At most eigen-energies, corresponding electronic states are localized states due to short localization length. In addition, relations between transmission coefficients and parameters of Fibonacci chain are qualitatively investigated.

Select

Electronic Structure and Photoelectric Properties of Rutile VO2 SONG Tingting, HE Jie, MENG Qingkai, SUN Peng, ZHANG Lei, LIN Libin 2008, 25(3): 365-372.  Abstract ( )   PDF (430KB) ( )   Electronic structure and photoelectrical properties of VO2, such as dielectric constant, absorption constant, refractive index, and conductance are studied with SCC-DV-Xα-ECM method. A broad band, in the upper part of which Fermi energy level is located, is formed by combination of 2p energy band of O and 3d energy band of V. VO2 exhibits metal characteristics. The peak around 0.8 eV is dominated by electronic intraband transition and the peak between 5~7 eV is mainly dominated by electronic band-to-band transition. The refractive index and extinction coefficients calculated consist with experimental results.

Select

Hysteresis Loops of FM Core/AFM Systems:A Monte Carlo Study HU Yong, DU An 2008, 25(3): 373-378.  Abstract ( )   PDF (513KB) ( )   Monte Carlo method is used to study hysteresis loops of FM/AFM systems with FM core embedded in an AFM matrix in a classical Heisenberg model. Magnetocrystalline anisotropy and exchange interaction are considered. It indicates that the shape of hysteresis loops changes with reverse maximal external field. The magnetization shows a jumping transition to metastable equilibrium with an increasing of external fields along positive z axis. The jumping range is independent of reverse maximal external field. With an increasing of AFM magnetocrystalline anisotrepy, exchange bias is obvious and larger external fields are needed for magnetization saturation. With an increasing of AFM exchange interaction, new hysteresis loops may appear in positive and negative external fields.