Archive

25 September 2005, Volume 22 Issue 5 Previous Issue    Next Issue

---

For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Select

A Lagrangian Finite Point Method for Two-dimensional Fluid Dynamic Problems SHEN Zhi-jun, SHEN Long-jun, LU Gui-xia, CHEN Wen, YUAN Guang-wei 2005, 22(5): 377-385.  Abstract ( )   PDF (545KB) ( )   In multidimensional fluid dynamics, methods based on mesh meet difficulties frequently, especially in problems with multimaterial media and large deformation grids.In this paper, a new meshless Lagrangian finite point method to compute unsteady compressible flows is presented. In this method discrete points are distributed in the physical domain, and are regarded as Lagrangian points with mass, velocity and energy. At a given point, a "cloud" of points in the vicinity are chosen and the relations between them are set. The Lagrangian fluid equations other than the SPH ones are discreted with the Godunov method in which the interface is in a position of connect line between the given point and its neighbors. To enhance robustness and accuracy of the algorithm, more neighbor cloud points are introduced and the least square approximation is facilitated in the simulation. Computed results are good for classical examples.

Select

An Implicit Method for the Pseudo-Compressibility Incompressible Navier-Stokes Equation BAI Peng, CUI Er-jie, ZHOU Wei-jiang, LI Feng 2005, 22(5): 386-392.  Abstract ( )   PDF (389KB) ( )   A pseudo-compressibility method developed by Rogers is used to solve the incompressible Navier-Stokes equation. Numerical flux is scattered through 3rd order Roe scheme and the 2nd order Harten-Yee TVD scheme separately. In order to accelerate convergence, several implicit methods(ADI-LU, LGS, LU-SGS) are accepted. Efficiency of different methods are shown as a classical flowfield around a cylinder in low Re(Re=200). Roe scheme is used to simulate two low speed unsteady problems:Low Re flowfield around a rotational cylinder(ω=1) and flowfield around a pitching NACA0015 airfoil with identical pitching rate.

Select

A High-order Accurate Scheme WCNS-E-5 Applied toBody Heat Transfer Distributions LIU Xin, DENG Xiao-gang, MAO Mei-liang, ZONG Wen-gang 2005, 22(5): 393-398.  Abstract ( )   PDF (371KB) ( )   A high-order accurate algorithm, which consists of WCNS-E-5 for inviscid term, fourth-order accurate scheme for viscous term and corresponding fouth-order boundary scheme, is carried out on the heat transfer distribution on body surface in a hypersonic viscous flow. The effect of grid Reynolds number on heat transfer at stagnation point and the influence of different boundary schemes on heat transfer distribution are investigated. A flow past a blunt cone with high attack angles is simulated numerically. It is shown that WCNS-E-5 is able to permit large spatial scale near the body. The physical phenomena captured by WCNS-E-5 with high-order accuracy are real, clear and high resolving in the whole flowfield. The heat transfer solutions are reliable and accurate.

Select

A Parallel Bisection Mesh Refinement Algorithm for Distributed Memory Parallel Computers LIU Qing-kai, ZHANG Lin-bo 2005, 22(5): 399-406.  Abstract ( )   PDF (414KB) ( )   We present a parallel bisection mesh refinement algorithm based on ALBERT (Adaptive multi-Level finite element toolbox using Bisection refinement and Error control by Residual Techniques). The goal is to develop a parallel adaptive finite element code suitable for distributed memory parallel computers or PC clusters. An overview on the basic strategy for the parallelization of ALBERT is given. Issues on the parallel mesh refinement are addressed. A modified mesh refinement algorithm, which can be implemented efficiently on distributed memory parallel computers, is proposed and its properties are discussed. Numerical experiments with parallel bisection mesh refinement algorithm are shown.

Select

Numerical Simulation of Gas and Aerosol Migration in Porous Media WANG Tie-liang, ZHANG Jian-xin, HUANG Liu-xing, WANG Zhan-jiang, ZHANG Zi-lu 2005, 22(5): 407-411.  Abstract ( )   PDF (268KB) ( )   In order to evaluate the migration of aerosols in porous media driven by gases, a dual porosity dual permeability mathematical model is proposed in symmetric cylinder coordinates.The processes of permeation, absorption, diffusion and heat exchange are considered. Calculated results show that aerosols could be contained in porous media well. Simulating experiments confirmed the prediction.

Select

An Algorithm for the Inverse of a Class ofBlock Tridiagonal Matrices RAN Rui-sheng, HUANG Ting-zhu, LENG Jin-song 2005, 22(5): 412-416.  Abstract ( )   PDF (178KB) ( )   The inverse of a class of block tridiagonal matrices is investigated. With the LU decomposition of the block tridiagonal matrix,an explicit expression of the block inverse elements is obtained. A relation between the inverse elements is found,and a new algorithm for inverting a block tridiagonal matrix is established. The computing complexity and computing time of this algorithm is lower than that of existed algorithms.

Select

A Conjugate Gradient Method for the Hyperbolic Inverse Heat Conduction Problem with Multi-variables XUE Qi-wen, YANG Hai-tian 2005, 22(5): 417-424.  Abstract ( )   PDF (378KB) ( )   We present a general numerical model for the hyperbolic inverse heat conduction problem with multi-variables, which includes thermal parameters and boundary conditions. A finite element numerical model is developed to formulate a direct problem and a discrete algorithm in the time domain is used for transient analysis. Including material inhomogeneity and distributive parameters, a least-square optimal model is developed for the inverse problem. A conjugate gradient method is adopted. Measurement errors and different time step are used to identify the parameters. Numerical validations are shown.

Select

Effect of External Noise on the Transport Propertyof Two-band Tight-binding Superlattices SHAO Jian-li, DUAN Su-qing, ZHAO Xian-geng 2005, 22(5): 425-430.  Abstract ( )   PDF (290KB) ( )   Within a two-band tight-binding model driven by a dc-ac electric field,we investigate the effect of external noise on the transport property of electrons in superlattices.We find that external noise can destroy the periodicity of the transient current and cancel the long-time average current peaks.The magnitude of the noise is usually in the order of ten percent of E0 (static electric field),which affects the transient and averaged currents strongly.Increasing the noise strength,the height of the current peaks decreases,and the width increases.A similar change appears while we increase the decay constant of the noise.

Select

Numerical Methods for the Abel Inversion of Temperature Field in an Arc Plasma SHAO Hua, ZHU Dan-ping, WU Yi-xiong 2005, 22(5): 431-436.  Abstract ( )   PDF (343KB) ( )   Concerning the Abel inversion in the analysis of arc plasma temperature field,three numerical methods are put forward.They are the cubic spline interpolation method,the Radon inversion method and the curve fitting method on dispersed data table.In validating the single apex and double apex functions,characteristics of these methods are analyzed.Precision,realization of program and the solution of integral singularity of these methods are discussed.It is shown that these methods have their own advantages in different cases in the calculating of actual temperature fields.

Select

Size Dependence of Structural and Magnetic Properties of Rhn(n=2~20) Clusters CHEN Jin-chun 2005, 22(5): 437-443.  Abstract ( )   PDF (415KB) ( )   The ground-state geometries of Rhn(n=2~20) clusters are calculated with a TB many-body potential in the Genetic Algorithm(GA). Based on the optimized geometries, we calculate the average bond length(R), average coordination number(CN), average binding energy Eb per atom. The average magnetic moment per atom μn and the average total density of states(DOS) of Rhn(n=15,17,18,19) clusters are calculated in a self-consistent tight-binding model considering 4 d, 5 s, 5 p valence electrons with both global and local neutrality. Our result reveals relations between structure and electronic and magnetic properties of small Rh clusters.

Select

The Pressure-Transient Characteristics of a Stress-Sensitive Triple-Medium Reservoir ZHAO Dong-mei, YAO Jun, WANG Zi-sheng 2005, 22(5): 444-448.  Abstract ( )   PDF (286KB) ( )   A test well interpretation model consisting of matrix, fractures and vugs is presented in which the permeability of vugs decreases exponentially with pressure drop. A mathematical model which takes into account the effect of wellbore storage and skin factor is calculated in a fully-implicit finite-difference scheme. It is shown that the dimensionless permeability modulus causes a increase of pressure and its derivative. The interporosity-flow factor determines the time of the interporosity flow. The storativity-ratio influences the width and depth of the "concave" in the pressure derivative. The effect of the outer-boundary differs from that of a normal triple medium. The skin factor affects the whole pressure and the "heave" in the pressure derivative curve, while the dimensionless permeability modulus mainly affects the later pressure and pressure derivative.

Select

An Eigenvector Method for the Mode Simulation of Optical Resonators and Beam Propagation CHENG Yuan-ying, JIANG Chao, WANG You-qing, HU Jin, LI Jia-rong 2005, 22(5): 449-455.  Abstract ( )   PDF (479KB) ( )   A novel Eigenvector Method(EM) for the calculation of resonator modes and beam propagation is developed.A new transit matrix for the optical resonator is obtained based on the Fresnel-Kirchhoff diffracted integral equation.The eigenvectors of the transit matrix,that represent multi-mode characteristics of the resonator,are calculated with the integral eigen-equation.The field inside or outside the resonator resulting from the eigenvectors can be derived by EM as well.The partition of grids,choice of shape functions,error and convergence analyses are discussed.It shows that a suitable partition of grids and choice of shape functions are of benefit to increase calculation rate,precision and stability.

Select

Parallel Unstructured Mesh Generation SI Hai-qing, CHENG Juan 2005, 22(5): 456-464.  Abstract ( )   PDF (846KB) ( )   A parallel unstructured mesh generation method is studied. Lohner's advancing front domain-splitting algorithm is improved so that the subgrids and their boundaries are more favorable for grid generation. An optimization strategy of subdomain's boundary is presented to improve the smoothness of the boundaries and the quality of grids. The conditions for receiving new points and elements are developed in the course of grid generation in subdomains. And a new strategy which receives new elements and refuses new points during the interface grid generation is presented,which saves calculation time.

Select

An Application of the Multi-block Patched Grid Technique in Electromagnetic Scattering Problems HE Xin, CHEN Jian-qiang, MAO Mei-liang, Deng Xiao-gang 2005, 22(5): 465-470.  Abstract ( )   PDF (500KB) ( )   Multi-block patched grids in conjunction with a finite volume time domain (FVTD) algorithm are used to solve classic multi-body electromagnetic scattering problems. The governing equations of the Maxwell equations are cast into three-dimensional general curvilinear coordinates. The approach uses four-stage Runge-Kutta scheme for time integration and flux vector splitting based on eigen structure of flux Jacobian matrices for spatial discretization. Monotonic upstream shemes for conservation laws (MUSCL) scheme for interpolation is used for the dependent variable. The resolution for temporal discretization is second order and that for spatial discretization is third order. Numerical results for the radar cross section(RCS) of a classical configuration agree well with the analytical results. And the results for multi-body calculation agree well with that in references. It shows that the algorithm developed is able to simulate complex topology configuration (including multi-body) problems.