We propose a method for three-dimensional inversion imaging of unknown magnetic sources in near-field conditions. Considering that most magnetic sources are not only magnetized with background magnetic field, but also have strong remanence, we convert magnetic field on observation surface into magnetic field vector anomaly modulus, and establish objective function to optimize solution to get the best match for magnetic field characteristics. Simulations and experiments show that the method eliminates effectively influence of residual magnetism on inversion results, and realizes imaging of magnetic susceptibility distribution of multiple magnetic sources in near field. It shows that the proposed method can be used to detect position and shape of unknown magnetic body.

A finite-difference time-domain (FDTD) method combined with Newmark algorithm in finite-element method for analysis of electromagnetic characteristics in dispersive media, named as extended Newmark-FDTD method, is presented. In the method, a unified time-domain updated formula can be applied to typical kind of dispersive model, i.e., Debye, Drude and Lorentz medium, and to novel dispersive models, i.e., modified Lorentz, quadratic complex rational function model and hybrid dispersive model as well, which has higher accuracy and better stability than traditional center difference scheme. Finally, validity of the algorithm is verified by several examples.

Two-dimensional potential energy surface (PES) of Be-CO complex was calculated with single and double excitation coupled-cluster theory with noniterative treatment of triple excitations[CCSD(T)], and in combination with large basis sets. The mixed basis sets, namely augmented correlation-consistent aug-cc-pVQZ for C and O atoms, aug-cc-pCVQZ for Be atom, and an additional (3s3p2d2f1g) set of midbond functions were used. A single global minimum with a depth of -69.21 cm^-1 located at R_e=8.29a₀, θ_e=115.42° is found. And the PES exhibits weak anisotropy. Rovibrational energy level structure of Be-CO complex is investigated. Spectroscopic parameters of the complex are calculated.

In large eddy simulations (LES), a flat ground model and rough wedge ground models with different wedge heights were adopted to investigate near-surface wind field characteristics under condition of time-varying upstream inflows. In both flat ground model and rough wedge ground models, simulated results show that there is downdraft in peak period of gusty wind and updraft in valley period, respectively. Intensity of downdraft/updraft flows are related to ground roughness in upwind areas and amplitude of inflows. It follows that wind velocity and direction in atmospheric boundary layer always change over time in time-varying upstream inflows, which enhances transportation of mass and energy in actual atmospheric boundary layer.

A discrete Boltzmann model is presented for detonation simulation. It consists of a discrete Boltzmann equation and a phenomenological reaction rate equation. In physical modeling, it is equivalent to a traditional Navier-Stokes model and a coarse grained model for thermodynamic non-equilibrium behavior. Compared with traditional fluid model, it provides more dynamic information and more kinetic information as well. The model adopts 16 discrete velocities, which has high computational efficiency. Additional degrees of freedom are introduced so that it can be used to simulate various detonations with different specific heat ratios. Several classic examples of detonation are simulated to validate the model. It shows that besides detonation dynamics where traditional hydrodynamic model works, it can also be used to study non-equilibrium effects where traditional fluid model does not work.

Optical limiting (OL) and dynamical two-photon absorption (TPA) of 4,4'-bis(di-n-butylamino)stilbene (BDBAS) molecules in chirped femtosecond laser pulses are studied by solving Maxwell-Bloch equations with an iterative predictor-corrector finitedifference time-domain (FDTD) method.It shows that both sign and magnitude of chirp rate influence greatly spectrum evolution and OL behavior.Spectra exhibit obvious carrier frequency shifts depending on sign of chirp rate,blue shift for positive chirp rate and red shift for negative chirp rate.As absolute chirp rate increases,shift becomes more obvious,OL window gets narrower and saturation of output intensity becomes greater.Interestingly,self-induced transparency (SIT) appears as a negative chirp rate reduces to a certain value (-0.025 fs^-2).Dynamical TPA cross section is reduced as chirp effect is considered.It provides a method for controlling nonlinear optical absorptions.

Mature long distance theory of vibration energy collision metastasis was applied to massive molecular system. A collision theory of ²³⁵UF₆ and ²³⁸UF₆ isotope molecules was established with quasiclassical method. v₃ vibration energy near resonant energy transfer process of ²³⁵UF₆ and ²³⁸UF₆ isotope molecules was studied. Resonance functions of energy difference,resonance transfer probability and resonance transfer rate as functions of temperature were obtained. It shows that they decrease with increase of temperature. Collision molecular translation decreases resonance transition probability and rate. It provides a theoretical basis for controlling selective loss processes caused by vibration-vibration transfer. It provides a reference for separation of uranium isotopes.

Two methods(SPH and ALE) are used to simulation of droplets impacton PMMA.Deformation of droplets and failure of PMMA are compared.It shows that the surface failures in two methods agree with Brunton's experiment.Feasibility and accuracy of two methods are proved.SPH method shows better ability in simulating liquid-solid impact.Then,a rain ball impact the edge of airscrew of a flying aircraft is analyzed with SPH method.Two engineering techniques are proposed to protect integrity of airscrew.

To maximize utilization of ultra high pressure jet energy,ultra high pressure jet flow field is studied with numerical simulation 0n different nozzle combinations.According to bottom flow field velocity vector and bottom hole pressure distribution,flow structure and drilling of nozzle combinations are analysed.A combination of three vertical edge nozzles has high efficiency on rock but is ineffective in cleaning the bottom and it results in wall erosion severely.Center plus a nozzle can clean the bottom and solve the problem of anti.wall erosion,but it requires greater high-pressure fluid displacement.Two vertical side nozzles and a center tilt nozzle or a vertical edge and a central nozzle combination is more favorable.A reasonable nozzle combination is essential in improving drilling efficiency.

Reverse voltage characterizations of 4H-SiC PiN diodes with junction termination extension(JTE) are simulated by using a two-dimensional device simulator(ISE-TCAD 10).0.4H-SiC PiN diodes with JTE are fabricated with a planar fabrication process based on simulation.Good consistency between simulation and experiments was achieved.It shows that a 4H-SiC PiN diode with optimized JTE edge termination can reach a breakdown voltage of 1600 V,which is more than 90 percent of ideal parallel plane junction breakdown voltage.

High-order conservative remapping method is developed to improve flow information exchange accuracy of window embedment technology on non-matched grid-block interface with preservation of conservative property and robustness.Remapping methods with various order of accuracy combined with various stencil selection strategy are compared.Constant distribution,linear and quadratic polynomial distributions are tested for reconstruction of conservative variables on interface.Accuracy and efficiency of linear polynomial WENO remapping are balanced well for engineering application.Numerical study of DLR-F4 wing-body configuration with a mending plate patched on the wing is conducted by a in-house developed code NSAWET.A sharp pressure jump brought by the mending plate is predicted.

A novel finite-difference time-domain(FDTD) method combined with semi-analytical recursive convolution (SARC) algorithm in digital signal processing(DSP) techniques is presented to analyze electromagnetic scattering by dispersive media.Absolute stability,high accuracy,less storage and high effectiveness are retained while a unified update formulation is possessed.It can be applied to analysis of general dispersive media provided that the poles and corresponding coefficients in dispersive medium are given.Finally,the proposed SARC-FDTD approach is validated.RCS of an object coated with plasma are calculated.

With characteristics of 4H-SiC,a double base epilayer 4H-SiC bipolar junction transistors(BJTs) is investigated.By analyzing build-in electric field in the base region and the base transit time,the device is numerically calculated in two-dimensional models according to orthogonal experiments.A mean range analysis is made to find optimized structure of 4H-SiC BJTs.It shows that common emitter current gain with negative temperature coefficient is about 72 and it remains high in a wide range of collector current.

A mathematical model and a program are developed to calculate neutron yields, energy spectrum and angular distribution of D (d, n)³He reaction in a thick deuterium-titanium (TiD_x) target as incident deuteron energy lower than 1.0 MeV. D(d, n)³He reaction cross section from nuclear data tables and stopping power derived with SRIM-2003 code are adopted in the calculatoin of neutron production of an accelerator-based D(d, n)³He reaction neutron source. Integrated neutron yields, neutron energy spectrums and angular distribution are obtained.

In order to solve EMC problems for multiple antennas mounted on airborne platforms with limited computer resources, a multilevel fast multipole algorithm (MLFMA) with adaptive number of levels is implemented based on Electric Field Integral Equation(EFIE). For the analysis of coupling between antennas, more reasonable arbitrary isolation is adopted instead of traditional isolation. BiCGStab(l) combined with near-field preconditioner is employed which improves efficiency of the MLFMA. Radiation pattern and isolation of ultra-shortwave antennas on a full-scale Boeing 747 aircraft model are obtained and discussed.

To overcome shortcomings of traditional inverse analysis method (TIAM), a fast and reliable searching scheme is used to find elements passing through die entrance radius during deformation process. An efficient stress-strain relation for continuous uniaxial tensile test is introduced to update stress distributions. Constitutive equations avoid complexity of incremental FEM based stress/strain updating algorithms, and effects of die entrance radius on deformation history are considered. Numisheet'93 square box drawing benchmark demonstrates that the constitutive equations significantly enhance prediction of stress distribution compared with incremental FEM based software DYNAFORM.

High order weighted essentially non-oscillatory finite difference schemes (FD-WENO) are applied successfully to numerical simulation of gravity-driven high density ratio Rayleigh-Taylor instability problems and laser ablative Rayleigh-Taylor instability problems in two dimensions. It provides important references to numerical study of inertial confinement fusion (ICF) as well as to other high-tech fields. High order FD-WENO schemes are applicable to numerical simulation of ICF inplosion.

Navier-Stokes calculation on multi-block is performed to calculate drag of the DLR-F6 wing-body configuration with CFD software TRIP2.0.Structured grids(1-to-1) and test results used are from Drag prediction workshop Ⅱ (DPWⅡ). Referenced numerical results are obtained with CFL3D. Effects of mesh density and turbulent models on aerodynamic characteristics and pressure distribution are carefully studied. Results are verified by experimental data and CFL3D results. Grid refinement leads to convergent results in SST turbulent models. It is demonstrated that turbulent models have little influence on pressure drag, but obvious influence on friction drag. The turbulent model and grid density have little influence on pressure distribution.

The static power and ground(P/G) network is analyzed by a combination of compressed equivalent circuit modeling and random wall algorithm.A model of power and ground network is obtained by parameter extraction and modeling over whole chips.The method builds an equivalent model for original network and uses random walk method to solve the simplified network.As a result,the improved compressed random walk algorithm saves CPU time greatly.The speed of the algorithm is more than two order of magnitude faster than the normal random walk algorithm.

A class of meshless methods for heat conduction equations are constructed.They can be performed on structured or unstructured meshes.The methods are conservative and consistent.They have at least the first order accuracy when performed on irregular quadrilateral or triangular meshes,and have the second order accuracy when performed on rectangular or uniform parallelogram meshes. These meshless methods are suitable and efficient in solving linear or nonlinear parabolic problems on irregular quadrilateral meshes or mixed meshes, especially in solving two-dimensional three-temperature radiation heat conduction equations on irregular and mixed meshes.

Based on a high-order compact upwind scheme,a high-order shock-fitting finite difference scheme is studied for numerical simulation of the generation of boundary layer disturbance waves due to free-stream waves.Both steady and unsteady flow solutions of the receptivity problem are obtained by computing full Navier-Stokes equations.Numerical simulation of receptivity to free-stream disturbances for hypersonic boundary layers is performed.

Resonance absorption of p-polarized electromagnetic wave by mode conversion in magnetized inhomogeneous plasma is investigated numerically as external magnetic field is perpendicular to density gradient.Different from an unmagnetized inhomogeneous plasma,the mode conversion coefficient in a magnetized inhomogeneous plasma depends on a cooperation of the incident direction,the density gradient direction and the direction of external magnetic fied.

With electric potential of three electrodes, discrete equations of surface electric charge density was founded with boundary element integral equations. The distribution of surface electric charge on the electrodes was calculated by solving a linear equation group. Then the spatial distribution of the potential and the electric field are obtained. In vacuum, the edge effect of a double glow discharge was analysed.

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.

A self-heating model is presented to predict the high-frequency performance of AlGaAs/GaAs heterojunction bipolar transistors (HBT's) including high current and thermal effects. A base pushout effect is discussed at high current region. And in this case, the lattice temperature, the cut-off frequency and the maximum frequency versus the collector current density are achieved.

An analytical non-linear model including surface-state effect is proposed for 4H-SiC power MESFET's with which the impact of suface damage at the ungate recess region caused by the dry-etching process on the output steady-state characterization can be illustrated clearly.The model has the advantage in very simple calculations over the 2D numerical simulations, therefore suitable for process analysis of SiC power MESFET's.

A new method to simulate flows with patched grids is introduced which is based on second-order Godunov method and Euler equations,and conservation across patch boundaries is satisfied.Using the method,the supersonic flows of bind-rocket and complex flows between two objects are simulated.Computation results are in agreement with experimental data,and describe the complex flows rightly such as the crossing and reflex of shocks.This conservation method with patched grids based on second-order Godunov method and Euler equations is one of effective methods for numerical simulation.

An approximate expression for escape probability for Doppler Profile lines in a cylindrically expanding medium is obtained in this paper. The complicated quintuple integral griving escape probability is approximated by a simple integral which has a Gauss-shaped integrand. The largest error is no more than 7%.

In order to simulate the cooling of electronic devices by solid-liquid phase change materials (PCM) the problem on two-dimensional melting heat transfer in a rectangular enclosure with discrete heat sources on one of its vertical walls has been solved numerically.Effect of Stefan number on the solid-liquid interfacial shape and wall temperature varition along the height of the wall are also discussed.

The Ray-tracing technique is useful to decrease computing time.