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25 March 2005, Volume 22 Issue 2 Previous Issue    Next Issue

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Exact Nonreflecting Boundary Conditions for Exterior Problems of the Hyperbolic Equation HAN Hou-de, ZHENG Chun-xiong 2005, 22(2): 95-107.  Abstract ( )   PDF (516KB) ( )   An artificial boundary numerical method for the exterior problems of the hyperbolic equation is considered.Three kinds of equivalent exact nonreflecting boundary conditions are derived on a circular artificial boundary.Numerical examples are presented and effectiveness of these artificial boundary conditions is demonstrated.

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Discontinuous Finite Element Methods for Solving Hydrodynamic Equations YU Xi-jun, ZHOU Tie 2005, 22(2): 108-116.  Abstract ( )   PDF (509KB) ( )   The discontinuous finite element method with first, second and third order accuracy on triangular meshes on two-dimensional domain is applied to simulate hydrodynamic equations. The calculation results are compared with those from difference methods. It is reckoned that the discontinuous finite element method has advantages in solving hydrodynamic problems with complicated boundary conditions or a domain with a complicated boundary.

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Upwind Compact Schemes for Hamilton-Jacobi Equations TIAN Bao-lin, FU De-xun, MA Yan-wen, LI Xin-liang 2005, 22(2): 117-122.  Abstract ( )   PDF (282KB) ( )   Based on the close relationship between Hamilton-Jacobi (H-J) equations and hyperbolic conservation laws,a high-order numerical method is developed to solve the H-J equations in the 3rd order and 5th order compact schemes.The upwind compact schemes are tested on a variety of one-dimensional and two-dimensional problems,including a problem related to the Richtmyer-Meshkov instability accelerated by planar shocks.Numerical results show that these schemes yield uniform high-order accuracy in smooth regions and satisfactorily resolve discontinuities in the derivatives.Moreover,since the present methods have less numerical dissipation than WENO scheme with the same order,they could be used to solve the H-J equations more accurately in the simulation of multi-scale complex flows.

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High-order Schemes for Viscous Hamilton-Jacobi Equations CAI Li, FENG Jian-hu, XIE Wen-xian, WANG Zhen-hai 2005, 22(2): 123-129.  Abstract ( )   PDF (320KB) ( )   Second-order and fourth-order methods for approximate solutions of viscous Hamilton-Jacobi equations are developed on the basis of the weighted essentially non-oscillator (WENO) scheme.By modifying the numerical flux,constructing the second-order approximation based on nonlinear limiter and fourth-order approximation based on Taylor expansion for viscosity term, the one- and two-dimensional viscous Hamilton-Jacobi equations are solved successfully. Numerical tests demonstrate the desired high-resolution,robustness and non-oscillatory behaviors of the schemes.

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Spatiotemporal Chaos Control in Coupled Bistable Map Lattice Systems YUE Li-juan, SHEN Ke 2005, 22(2): 130-136.  Abstract ( )   PDF (440KB) ( )   The suppression of spatiotemporal chaos is realized by using variable feedback techniques in coupled bistable map lattice systems.Numerical simulations indicate that the chaos in a bistable map system and the spatiotemporal chaos in a coupled bistable map lattice system could be suppressed to the fixed point or the periodic orbits by using different feedback techniques and strengths.In addition to the fixed point of a local bistable map system the feedback control method does not require a priori dynamics information of the coupled bistable map lattice system.The method appears useful in controlling turbulence of coupled bistable map lattice systems.

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An Alternating Segment Implicit Method for Burgers Equations WANG Ting-chun, ZHANG Lu-ming 2005, 22(2): 137-142.  Abstract ( )   PDF (232KB) ( )   A two-level implicit scheme for Burgers equations is shown,whose truncation error is O(τ2+h2) (where τ is time step and h is space step).An alternating segment method is proposed and its unconditional linear stability is proved.The new method is free from nonphysical oscillations and suitable for parallel computers.A numerical example shows that the method has good applicability and high accuracy, in particular, it is more accurate when diffusion coefficient is small.

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The Application of Computational Singular Perturbation in Reduced Combustion Reaction Systems LIU Jie-ping, CHENG Xiao-li, WANG Qiang 2005, 22(2): 143-148.  Abstract ( )   PDF (316KB) ( )   A reduced chemical kinetics model for typical combustion reaction systems is derived by means of the Computational Singular Perturbation (CSP) method.The combustion reaction governing equations are employed to construct ideal basis vectors,with them the coupling between the fast mode and the slow mode is decoupled properly.Several significant parameters are defined,such as the participation index,the radical pointer,and the importance index.Then the state equations of the fast modes and the reduced chemical kinetics model are obtained.A typical mixed combustion reaction system of CO-CH4-Air is calculated,and the results show that the reduced combustion reaction system obtained by CSP method approximates the original system well.

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Mesoscopic Transport Through a Toroidal Carbon Nanotube and a Quantum Dot Coupled System ZHAO Hong-kang, WANG Qing 2005, 22(2): 149-154.  Abstract ( )   PDF (289KB) ( )   The mesoscopic transport through a quantum dot and a toroidal carbon nanotube (TCN) coupled system is investigated with the nonequilibrium Green's function technique.The coherent tunneling is strongly related to the energy structures of the TCN and the quantum dot.The Aharonov-Bohm effect causes energy levels of the TCN to change periodically,and the tunneling current oscillates with the magnetic flux.The detailed nanostructure of TCN exhibits metal-semiconductor transition,and this behavior is reflected in the output current.The matching-mismatching of quantum levels of the sub-systems plays important role in the mesoscopic transport.

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Radiative Lifetimes of Rydberg States 6sns 3S1 and 6snd 3D1 of HgI LIANG Liang, ZHOU Chao, WANG Yong-chang 2005, 22(2): 155-158.  Abstract ( )   PDF (180KB) ( )   Natural radiative lifetimes of 6snd 3S1(n=11~25) and 6snd 3D1(n=12~24) Rydberg series of neutral mercury are calculated by means of multichannel quantum defect theory (MQDT). The lifetime of 6sns 3S1 series can be approximated by τ=0.814v2.835(ns) and that of the 6snd 3D1 series by τ=0.302v2.926(ns), where v is an effective quantum number.

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A Quantitative Relationship Between pKa and Molecular Vibration Intrinsic Frequency of Nonmetal Binary Hydrides QIU Ming-hua, ZHAO Li-gang, LONG Yun-fei, LUO Juan 2005, 22(2): 159-162.  Abstract ( )   PDF (207KB) ( )   The intrinsic frequency of molecular-vibration of nonmetal binary hydrides is calculated with mechanic vibration theory.Both the fundamental frequency (ω0) and the summed frequency (Σωi) are used as molecular structural indices,and the established model:pKa=A0+A1ω0+A2Σωi is applied in the quantitative relation analysis.It is shown that the estimated correlation coefficient between pKa values and the indices in the data set is larger than 0.995.Comparing the period values with the experimental values of pKa,the mean absolute error is estimated to be less than 1.82.

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A Numerical Simulation of Profile Controlling and Flooding with Weak Gel XU Bing, CHENG Lin-song 2005, 22(2): 163-170.  Abstract ( )   PDF (325KB) ( )   A three-dimensional,three-phase,eight-component mathematical model based on the component model and the black oil model is presented. The model considers main factors,such as gravity,capillary force,compressibility of fluid and rock etc.An improved IMPES (implicit pressure, explicit saturation) method is applied in which the phase pressure is calculated implicity and the phase saturation is calculated with high order accuracy.Based on this mathematical model,a numerical simulator is developed for the profile controlling and flooding with weak gel.

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A Design of 3D Spot-size Converter Based on a Rib Waveguide Structure ZHANG Xi-fei, XIAO Jin-biao, CAI Chun, ZHANG Ming-de, SUN Xiao-han 2005, 22(2): 171-178.  Abstract ( )   PDF (403KB) ( )   A 3D trapered spot-size converter (3D-SSC) on a rib cross-sectional optical waveguide, one of the key components in photonic devices connecting with single mode optical fibers,is investigated through simulating lightwave transmission in this component based on 3D-FD beam propagation method.Geometry parameters,such as laterally boundaries,length,width of the large section,thickness and those of the transitional optical waveguide for connecting SMOF to 3D-SSC are discussed and analyzed.The simulation shows that the insert loss of 3D-SSC can be lower than 2 dB as the width in the area of 11.5 μm~13.5 μm and the thickness in the area of 4.5 μm~6.5 μm at the large end of the taper when the taper length is in the region of 200 μm~500 μm.The capability and the alignment tolerance of the 3D-SSC is better than those of the planar SSC,and the 3D-SSC with a nonlinear lateral boundary acquires lower insertion loss than that with a linear lateral boundary.It is found that the 3D-SSC converts gradually the guided modes from multi-mode to single mode finally.

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A Numerical Calculation of Fission Chain Statistical Fluctuation with Wide-pulse Neutron Injection XU Nai-xin, TANG Min-jun 2005, 22(2): 179-183.  Abstract ( )   PDF (205KB) ( )   With wide-pulse neutron injection the fission chain fluctuates statistically.A calculation approach is presented, in which numerical solutions of the statistical distribution Wn equations are disassembled and then synthesized.It makes the computation suitable for generalized conditions (with arbitrary time distribution,zero time (t0) injection probability distribution P(t0) and number probability distribution S(n) etc.).The equivalent conditions in practical physical models are discussed and expanded from single-medium to multi-medium.In addition, the average computing formulae for required parameters in solving Wn equations are given as well.

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An Integral Conservative Remapping Method for Two-dimensional Lagrange Meshes FU Shang-wu, DAI Zi-huan, WU Ji-ming 2005, 22(2): 184-188.  Abstract ( )   PDF (362KB) ( )   An effective rezoning method for two-dimensional Lagrange meshes, i.e., an integral conservative remapping method, is studied. The algorithm is described in detail. Calculation results are shown.