Archive

25 March 2006, Volume 23 Issue 2 Previous Issue    Next Issue

---

For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Select

Initial Transient Magnetic Field Distribution in an MFCG YANG Xian-jun, DONG Zhi-wei, ZHAO Qiang 2006, 23(2): 127-132.  Abstract ( )   PDF (313KB) ( )   An analytical scheme for the initial transient process in a simple helical flux compression generator, which includes distribution of the magnetic field in the hollow of the armature and current density in the helical stator, is derived with diffusion equations. The relationship among frequency of conducting current,roots of the characteristic Bessel equation and decay time in the armature is discussed. The skin depth in the helical stator is calculated and is compared with an approximation widely used in the magnetic diffusion process. Our analytical result is helpful to understand mechanism of the loss of magnetic flux in both armature and stator and makes significant suggestions to optimal designing performance of the helical flux compression generator.

Select

Mean Short Path of Network and Network Product ZHOU Yu-lin, YUAN Guo-xing 2006, 23(2): 133-136.  Abstract ( )   PDF (173KB) ( )   The mean short path of network is discussed. The mean short path of the network product is equal to the sum of the mean short path of the networks. Based on this we calculate the mean short path of several constructed networks.

Select

A Numerical Study of High-speed Impulsive Noise of Helicopter Rotors with the CFD/Kirchhoff Method ZHAO Qi-jun, XU Guo-hua, WANG Shi-cun 2006, 23(2): 137-143.  Abstract ( )   PDF (426KB) ( )   To improve the accuracy in the simulation of rotor flowfield and noise in the CFD/Kirchhoff method, a combination of the third-order upwind scheme(MUSCL) and flux-difference splitting scheme, instead of the second-order center-difference scheme which may cause larger wake dissipation, is employed and a N-S solver based upon embedded grids is developed. On the basis of the flowfield solution, a harmonic expansion approach is presented for rotor far-field noise. The approach gives an analytical expression of the integral function in the Kirchhoff formula and thus improves the interpolation efficiency and accuracy. A rotor high-speed impulsive(HSI) noise is calculated and a comparison with available experimental data is made, and good agreement was demonstrated. In addition, the HSI noise of helicopter rotors at different tip Mach numbers and on different observer locations is calculated and analyzed. The calculated results indicate a highly directional nature of the rotor high-speed impulsive noise with a maximum in the plane of rotor, and the impulsive feature of the high-speed noise radiation weakened rapidly with the increase of the directivity angle below the rotor plane.

Select

A Conjugate Gradient Algorithm for Density Reconstruction in High-energy X-ray Radiography XU Hai-bo, WEI Su-hua 2006, 23(2): 144-150.  Abstract ( )   PDF (351KB) ( )   A point spread function and a cost function are obtained with a physical analysis of the high-energy x-ray radiography. Taking the French Test Object model as an example, the conjugate gradient algorithm is applied to the density reconstruction in high-energy x-ray radiography, and the result is satisfactory. The algorithm starts at a simulation in radiography and searches for a maximum likelihood by comparing the simulated radiographs with the measured radiographs. To some extent, the algorithm overcomes the uncertainty in eliminating the blurting effects through a deconvolution process in reconstruction methods.

Select

An Inverse Heat Conduction Problem with Multi-variables in a Transient State with a Homotopic Regularization Method XUE Qi-wen, YANG Hai-tian, DU Xiu-yun 2006, 23(2): 151-157.  Abstract ( )   PDF (322KB) ( )   Taking Bregman D-Function as a regularization function, we present a general numerical model to identify the multi-variables, including thermal parameters and boundary conditions. A time stepping scheme is used for the transient analysis and a homotopy method is adopted to solve the process. Both the data with measurement errors and the initial value are used to indentify these parameters. The numerical validation exhibits good results.

Select

A Variational Calculation of Equilateral Triangle H3 and Tetrahedron H4 GUO Zhi-quan, WANG Kai-ming, WANG Hong-de, GUO Qiu, YU Yong-xin, GAO Shou-shan 2006, 23(2): 158-164.  Abstract ( )   PDF (232KB) ( )   With a variational method and a modified arrangmement channel quantum mechanics(MACQM) method, the energies of a equilateral triangle H3 and a tetrahedron H4 system are calculated. The result shows that as α=1.03 and R=1.74a0, the H3 system has a minimal energy of -1.58161 a.u.; as α=1.07 and R=1.60 a0, the H4 system has a minimal energy of -2.28097 a.u.. It shows that both structures could exist.

Select

Numerical Methods with Dynamic Structured Meshes for Unsteady Flows with Moving Boundaries ZHANG Yu-dong, JI Chu-qun 2006, 23(2): 165-170.  Abstract ( )   PDF (308KB) ( )   3D time-accurate Euler/Navier-Stocks equations for a cell with moving boundaries are established in a Cartesian framework. Based on the two-order Godunov scheme, numerical simulation methods on dynamic grids are established. To avoid grid motion induced error, the geometric conservation law (GCL) is satisfied numerically. The method is applied to simulate unsteady transonic flow about an oscillating airfoil (2-D) and an oscillating rigid rectangular wing (3-D). Computational results are in good agreement with the experimental data. The methods are effective and can be used to solve multi-body separate problems.

Select

Direct Monte Carlo Simulation of a Microscale Backward-facing Flow Qin Feng-hua, Sun De-jun, Yin Xie-yuan 2006, 23(2): 171-176.  Abstract ( )   PDF (367KB) ( )   A modified treatment for pressure boundary conditions in DSMC is shown, The microscale backward-facing gas flow is computed by a partitioned domain DSMC method and a general flow construction is obtained. It is shown that the recirculating flow region attached to the backward-facing step exists in the microscale flow with proper conditions while the region of separation on upper side does not. A discussion about the effect of flow parameters is given and a relationship between reattachment length and Reynolds number is obtained.

Select

An Explicit Algebraic Reynolds Stress Model for Anisotropic Buoyant Turbulent Flows LAI Xi-jun, WANG Zhi-dong, WANG De-guan 2006, 23(2): 177-183.  Abstract ( )   PDF (369KB) ( )   An explicit algebraic Reynolds stress model (EARSM) proposed by Wallin & Johansson was extended to simulate anisotropic buoyant turbulent flows. The collocated finite volume method was applied to solve the Navier-Stokes equations and the pressure coupling was treated in the SIMPLEC algorithm. A turbulent thermal mixing in T-junction flows was simulated to validate the model, A comparison with experiments and Fukushima et al's DNS results shows that the present model captures the characteristics of anisotropic buoyant turbulent flows. Meanwhile, the computation shows excellent numerical stability and the computation cost is only slightly higher than that of the eddy-viscosity turbulence model.

Select

An Algorithm of Selecting Delay Time in the Mutual Information Method LÜ Xiao-qing, CAO Biao, ZENG Min, HUANG Shi-sheng, LIU Xiao-guang 2006, 23(2): 184-188.  Abstract ( )   PDF (256KB) ( )   A concrete algorithm of selecting delay time in the state space reconstruction in the mutual information method is introduced. A simple and practical program algorithm based on a reticulate layer is established. An analysis on calculated result shows that the mutual information needs to be computed to a certain reticulate layer in selecting delay time. Therefore, the algorithm is simplified significantly. The Lyapunov exponents calculation of attractors(Rossler and Lorenz) verifies the validity of this algorithm.

Select

A Study on the Spin-ladder Model WU Jun-fang, ZHANG Chun-min 2006, 23(2): 189-192.  Abstract ( )   PDF (168KB) ( )   The eigenvalue and the two-particle scattering matrix are obtained in a spin-ladder model. They are solved with the coordinate Bethe Ansatz method in integrable. The eigenvalue equation is formed with the Schrödinger equation. Then the eigenvalue is solved as the wave function is given. Finally, the two-particle scattering matrix is calculated by the eigenvalue equation and the continuous condition of the wave function. The eigenvalues of one-particle, two-particle and N0-particle are solved, and the two-particle scattering matrix is obtained.

Select

A Numerical Analysis of Instantaneous Response of the CH4/O2/N2 Laminar Flamelet WANG Hai-feng, CHEN Yi-liang, CHEN Hua-lei, LIU Ming-hou 2006, 23(2): 193-198.  Abstract ( )   PDF (404KB) ( )   The instantaneous response of a laminar diffusion flamelet is investigated numerically. A detailed mechanism GRI-Mech 3.0(53-species and 325-reaction) is empolyed to describe the CH4 oxidation and NOx formation. A predication of steady flamelct structures is compared with the experimental data to validate the method. A step variation of strain rate is used to simulate the influence of a instantaneous flow field on the flamelet local structure. The response of flamelet structures(temperature and species concentration) to the strain rate variation is given and analyzed. We focus on the influence of the step size of the strain rate. It is found that the flamelet response to the strain rate variation is not symmetric,and the response time is inverse proportional to the strain rate variation as it is small. In addition, the mean response time of temperature is much longer than the flow time scale of a typical turbulent combustion field, which demonstrates the importance of unsteadiness in the numerical simulation of turbulent combustions.

Select

Backflow in an Inverse Twisted Nematic Liquid Crystal Cell ZHANGZhi-dong, JIANGLi, WEI Huai-peng 2006, 23(2): 199-203.  Abstract ( )   PDF (228KB) ( )   Based upon Erickson-Leslie hydrodynamic equations, we study an inverse twisted nematic liquid crystal cell, in which the liquid crystal is untwisted in the field-off state and twisted in the field-on state. The time evolution of director configuration and the velocity of flow are obtained. An abnormal director profile caused by the backflow appears after the switch of a holding voltage.

Select

Propagation of Light in a Supersonic Turbulence Boundary Layer CHEN Yong, LIU Jian, LI Shu-min, JIN Gang 2006, 23(2): 204-208.  Abstract ( )   PDF (481KB) ( )   Propagation of light in a supersonic flat turbulence boundary layer is numerically analyzed. The flow characteristics are studied according to the optic wave-front variance. The mass-weight averaging N-S equations are adopted as the governing equations of flow, and a two-equation turbulent model is employed. Light propagation is described by paraxial wave equations and solved by a phase-screen method combined with the FFT technique, Light intensity distribution and phase aberrations are given in order to show the optic aberrations as well as the flow characteristics.

Select

A Semivectorial Analysis of Optical Waveguides Based on a Variable Transformed Galerkin Method ZHANG Xi-fei, MA Chang-feng 2006, 23(2): 209-216.  Abstract ( )   PDF (345KB) ( )   A semivcetorial method based on a variable transformed Galerkin method is proposed for optical waveguides. It is successfully applied to analyze the eigenvalues of rectangular and rib optical waveguides. The modal propagation constants and field distributions of rectangular and rib waveguides are presented. The calculated results agree well with the published data. Adopting a proper variable transformation, the artificial boundary condition is avoided, and the polarization characteristics of the mode field are displayed.

Select

A One-dimensional Study of Un-stabilized Filtration Combustion in a Packed Bed ZHANG Gen-xuan, CHEN Yi-liang, LIU Ming-hou, YE Tao-hong, WANG Hai-feng 2006, 23(2): 217-223.  Abstract ( )   PDF (419KB) ( )   Gas filtration combustion in porous media differs substantially from the combustion with free flame. A one-dimensional model is proposed, and a perturbation theory is used for the combustion front velocity analysis of the methane-air premixed combustion in an inert packed bed, The temperature distribution is predicted for either fully-developed or transient combustion state, based on direct solution and Green's function method. Finally, computational experiments are given and the results are satisfactory.

Select

A Simple Method for Voxel Constructing and Material Ascertainment in BNCT Monte Carlo Dosimetry Calculations LI Gang, DENG Li 2006, 23(2): 224-230.  Abstract ( )   PDF (604KB) ( )   We introduce a simple method for voxel constructing and material ascertainment in BNCT(Boron Neutron Capture Therapy). The voxel model of a Snyder head phantom based on four materials, provides a good approximation. It keeps the conservation mass of skeletoncranium, brain and skin. The 4-material voxel model and 286-material voxel model with mesh sizes of 16 mm, 8 mm, 4 mm, are simulated respectively by the MCNP Monte. Carlo program. The result indicates that the 4-material voxel model is accurate. We also recommend a 5 mm mesh voxel model, which saves simulation time and keeps a good accuracy.

Select

A Simulation of the EAST MHD Equilibrium Configuration HUANG Qin-chao, WANG Hua-zhong, LUO Jia-rong, YUAN Qi-ping 2006, 23(2): 231-236.  Abstract ( )   PDF (371KB) ( )   The Tokamak equilibrium fitting numerical calculation code EFIT is modified to study the MHD (magnetohydrodynamics) equilibrium in an EAST device. The divertor configuration in the steady-state phase of the EAST device is simulated with the modified cede. A method is proposed to satisfy the free boundary equilibrium for non-symmetrical current, by using linear equation array with the current of poloidal field coils as the main confined condition and expected configuration as the auxiliary confined condition. It is shown that the method can be used to obtain the equilibrium configuration which is induced by non-symmetrical current, and to solve the non-convergence problem of a free boundary equilibrium.

Select

False Scattering and Ray Effect in Spherical Harmonics Approximation for the Radiative Transfer Equation ZHANG Hao-chun, YI Hong-liang, TAN He-ping 2006, 23(2): 237-242.  Abstract ( )   PDF (391KB) ( )   The false scattering and ray effect in spherical harmonics method, including P1 and P3 approximation, is studied. Physical models of parallel and oblique laser incidence into two-dimensional gray media are constructed and the temperature profile within the medium is investigated to examine the false scattering. The ray effect is analyzed by the net radiative flux in the boundary. Simulation results show that both false scattering and ray effect exist in the spherical harmonics method, and the ray effect is mitigated higher in P3 than that in P1 approximation. In addition, the ray effect in the spherical harmonics approximation mitigates with increasing optical thickness within gray medium.

Select

A Local Phase Control of Spiral and Spatiotemporal Chaos MA Jun, WU Ning-jie, YING He-ping, PU Zhong-sheng 2006, 23(2): 243-248.  Abstract ( )   PDF (642KB) ( )   A local phase compress scheme is applied to suppress spiral and spatiotemporal chaos in the Fitzhugh-Nagumo and Panfilov systems. In the numerical investigation, the compress signal is limited to a small area in order to control the global spiral and spatiotcmporal chaos with or without noise. The simulation shows that the system becomes homogeneous stable within a few of 50 time units. A practical control of defibrillation and pattern formation is discussed.

Select

Quantum Properties of the Superposition of Excited Coherent States LU Dao-ming 2006, 23(2): 249-252.  Abstract ( )   PDF (185KB) ( )   The superposition of two excited coherent states with identical intensity and different phases are constructed. Its antibunching effect and amplitude-squared squeezing are studied numerically. The result shows that as the light intensity and the excited photon number increase, the antibunching effect decreases and the amplitude-squared squeezing increases. The amplitude-squared squeezing is influenced by the phase difference.