Classical trajectories of a diatomic molecule system (CO) in laser fields are calculated in the symplectic scheme. The calculated results are compared with that with Runge-Kutta(R-K) approach. The vibration trajectories, phase trajectories and vibration energy of a diatomic molecule CO are analysed.
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The relationship between the slowness-curved-surface and the softening of the acoustic mode is discussed.The acoustic mode softening of cubic systems corresponds to the maximum slowness. The eigenvector in the soft mode corresponds to the polarization of acoustic mode. By solving the Christoffel equation, the maximum slowness and the polarization of the acoustic mode are obtained. The symmetry change of proper ferroelastic phase transition of cubic systems is determined by the solution of the Christoffel equation and the Curie principle.
A series of adaptive corrdinate transformation methods are proposed in which the grid angles are preserved approxi-mately, and the material interface is kept to be Lagrangian description and a minimum difference (in the least-squares sense)be-tween the mesh velocity and the fluid velocity is achieved. The new coordinate system is adapted to important features of flow fields.
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.
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.
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.
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.
Natural radiative lifetimes of 6snd ()~3S_1(n=11～25) and 6snd ()~3D_1(n=12～24) Rydberg series of neutral mercury are calculated by means of multichannel quantum defect theory(MQDT). The lifetime of 6sns ()~3S_1 series can be approximated by τ=0.814v~(2.835)(ns) and that of the 6snd ()~3D_1 series by τ=0.302v~(2.926)(ns), where v is an effective quantum number.
The Complex Terrain Dispersion Model(CTDM) developed by the American Environmental Protection Agency(EPA) is applied to Qinshan Nuclear Power Plant(QNPP) in China.The ground plume centerline concentrations of atmospheric pollutant in PhaseⅠ,Ⅱ and Ⅲ are calculated.The results are compared with that of wind tunnel experiments and a few field data.Two revising methods for LIFT are put forward.Model reliability test shows that the revising methods are more accurate.The ratios of calculated result to the measurement in the domain of 1/3.5～3.5 are:54.4% in CTDM,72.9% in revision A, 58.6% in revision B.In addition,the model sensitivity is analyzed.
Grand canonical Monte Carlo(GCMC) method is adopted to investigate the dependence of hydrogen storage capacitym 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 0.34to 0.61 or 0.88 nm the hydrogen storage capacity is improved effectively. As the inter-tube distance of SWCNTA approaches 1.7nm 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 nAy 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.
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.
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.
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.
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.
The fiber fine structure in solar radio bursts carries small-scale magnetic field information in the initial phase of the burst.We deal with fiber structures to analyze the frequency drift rate.The background is obtained by a wavelet transformation.With a subtraction of the background and a threshold processing,the fiber structures are seperated.We select continuous segments in each channel.The cubic spline interpolation is used to fit the intensity-time relation with which the moments of intensity maxima are determined.Finally,the drift rate is calculated with linear regression.The algorithm is used to calculate frequency drift rate of the radio fiber event on 21-April-2002.The mean frequency drift rate obtained is beween(0.041?0)～(-0.013?8)?GHz·s~(-1).
We developed a high performance algebraic solver for nonlinear systems discretized from two-dimensional energy equations with three temperatures by a nine point scheme.The main idea is to solve the system by an inexact Newton method and preconditioned Krylov subspace methods in the frame of PNK and JFNK methods.Numerical experiments show the efficiency of the algebraic solvers.It is shown that our PNK method is 6 times faster than the nonlinear block Gauss-Seidel method. The JFNK and PNK methods are also compared.
The time step control in two-dimensional three-temperature hydrodynamic calculations is studied.Based on numerical stability and accuracy we propose several conditions that restrict the time step.These conditions change the time step automatically in computation so that the calculation proceeds with the most economical and reasonable time step.Numerical results are shown to demonstrate the efficiency of the method.
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.
