A fast directional boundary element method for large scale wideband elastodynamic analysis is developed. Directional low rank property of elastodynamic kernels is shown which serves as the theoretical basis of its fast directional algorithm. By only considering S-wave number, interactions of different nodes are divided into low-frequency interactions and high-frequency interactions, and the latter is further divided into interactions with directional wedges on which the directional low rank property is applied. Low-frequency interactions are computed in same manner with that in kernel independent fast multipole BEM for elastodynamics, and translation matrices for different directional wedges are calculated efficiently by coordinate frame rotations. Thus harmonic responses for any frequencies can be computed efficiently. Numerical examples show that the computational complexity for wideband elastodynamic problems are successfully brought down to O(N log^αN). It can also be applied to transient elastodynamic analysis combined with convolution quadrature method.

Equation of state and phase transformation of ZnO in wurtzite structure and NaCl structure under high pressures are studied using density function theory(DFT) formalism.We analyze structural properties,including lattice constant,electronic density of states and band gap.The results are in good agreement with experimental and other theoretical results.It is found that the calculated phase trasformation pressure of metallic oxides using local density approximation(LDA) is generally higher than experimental results.Calculated results using generalized gradient approximation(GGA) are in good agreement with experiments.

An uncoupled method based on an implicit dual time-step approach for nonequilibrium flows is developed.Flow and reaction are separated by using operator-splitting method.Flow equations are solved by a dual time-step approach and source equations are solved by 2nd order trapezoidal formulas.A source-eliminating method is designed to remove error imposed to the solution by chemical source,which is very effective to assure time precision of flow-solving.Analysis and computations suggest that the method maintains efficiency of dual time-step approach as well as precision of unsteady computational results.

An integrated gradient total symmetry-preserving(IGTSP) scheme for momentum equations of Lagrangian hydrodynamics in cylindrical coordinates is presented.The scheme inherits advantages of both IGT and IGA schemes,that is,the scheme not only overcomes nonsymmetry of the IGT scheme but also has a momentum conservation error of order O(h),one order higher than that of IGA scheme.A number of numerical examples are tested to demonstrate advantages of IGTSP scheme.

Material properties are investigated on ballistic performance of tungsten-alloy rods with two-dimensional numerical simulations by program LS-DYNA.In an elastic-plastic hydrodynamic material model,primary parameters of the rod includes failure strain,yield stress and shear modulus,etc.Penetration is studied through simulation of a tungsten-alloy rod impacting on a semi-infinite aluminum-alloy target.It is shown that failure strain shows dominant effect on penetration. Numerical simulations of penetration within impact velocity regime ranging from 785 m/s to 1 924 m/s are performed.Numerical results are in good agreement with experimental data.

In a cylinderical coordinate system, integrated gradient method is an effective discrctization for equations of Lagrangian hydrodynamics. In the method IGT (Integral Gradient Total) scheme does not preserve spherical symmetry while IGA (Integral Gradient Average) scheme overcomes nonsymmetry in cylinderical coordinate system. However, IGA results in abnormally large acceleration in case of large mass ratios, where the mass of one subcell around a node is smaller than that of the other three subcells. If boundary force between neighbouring cells is taken as weighted mass average, IGA scheme is equivalent to IGT scheme in both a planar problem and a cylinderical problem even if there exists a large mass ratio. It is shown that IGT scheme preserves total momentum conservation but IGA scheme does not. Numerical results demonstrate advantages and disadvantages of the two schemes.

Self-sustained oscillation of supersonic cold flowover cavities of scramjets is investigated.Unsteady flowfields are calculated by hybrid RANS/LES method.The key cavity parameters,cavity aft wall angle andthe ratio of cavitylengthto depth,are considered.The hybrid model captures the large scale unsteady characteristics and reveals the evolution process of cavityfree shearlayer.Pressure fluctuation spectra agree well with theoretical prediction.The hybrid RANS/LES data indicate that both cavity shape and size have significant effects on oscillation.Asthe ratio of cavitylengthto depth decreases,the oscillations tend to concentrate on several modes,and the frequency of maximumoscillation amplitude shifts to higher values.Most oscillations are greatly attenuate as the cavity aft wall angle decreases.Compared with a steep aft wall cavity,only highfrequency mode remains inthe cavity with small aft wall angle.

A nine-point rezone strategy is presented,which improves geometric quality of computational grids and keeps the rezoned grids close to Lagrangian meshes.The scheme is proved an approximation to elliptic equation with spherical symmetry.Numerical examples demonstrate robustness and effectiveness of the scheme in ALE (Arbitrary Lagrangian Eulerian) calculation of high speed impact and denotation driving.

In a sparse linear system derived from two-dimensional three-temperature energy equations, the diagonal dominan varies greatly from row to row and so is the magnitude of the elements. We provide a new scaling method to improve the diagonal dominance. As ILUT is used to the derived linear system, it reserves the number of elements in each row and several relatively large elements related to the photon are dropped due to the large difference among elements. To improve the equality of the ILUT, we provide a new method named multiple row ILUT (MRILUT), in which multiple rows are computed before dropping. The provided methods are embedded into a preconditioned Krylov subspace method to solve the actual two-dimensional energy equations with three temperatures. The number of iteration at each time step and the total computation time are both greatly reduced.

The constitutive model and its parameters of concrete and rock with damaging variables are given referring to[1,2],and coded into a 2-D elastic-plastic finite element program named LTZ-2D.With this program,the problem of projectile and kinetic bullet penetrating concrete and rock targets is numerically simulated.The results of simulation are compared with those of experiments.

A parallel solver for circulant block tridiagonal systems on distributed memory multicomputers is developed.The algorithm is based on matrix block operations.The implementation of this algorithm invokes BLAS3 subroutines.The complexity of the algorithm is analyzed.A sufficient condition guaranteeing the processes not to break down is given.The numerical experiments on a distributed memory multicomputer YH3E show that this algorithm has a high parallel efficiency.

A numerical approach is presented for simulating the stability of harmonic resonance overvoltage in power systems and the relationship is discussed between the stability of harmonic solutions and the change of parameters of system by using the methods of Galerkin and Runge Kutta.It can be used for describing further bifurcation phenomenon in power systems.

A numerical approach is presented for simulating the quality of natural ventilation in an apartment unit with three bedrooms and one hall by using algorithm of Simpler and Artificial compressing method based on blocked interior spaces,which obtained the main data on the distribution of laminar-flow field in a housing unit. The application software created accordingly applies universally,which provides an effective means for an alyzing,optimizing and evaluating the quality of natural ventilation in housing design.

The computational program of chemical kinetics of KrF^* excimer laser pumped by e-beam is modified. The kinetics and energy deposition for the mixture system of Ar, Kr and F₂ pumped by proton-beam is calculated. The results show that deposited energy is about 50 times as much as by e-beam-pumping for the same pressure, the same mixture of the gases and the same current density.

The scattering of waves from a cylindrical obstacle burried in the dielectric half-space can be investigated by many means. One of them is discrete method. But it is difficult to deal with the radiation conditions on the artificial boundaries of finite calculating region. To eliminate the effects of waves reflected from the artificial boudaries, an Artificial Transmitting Boundary Method was given by seismology circles and has been applied to some scattering problems successfully/In this paper, as a trial, the method mentioned above is combined with Finite Element Method and applied to give out the near-field solutions. Then, making use of the results, the far-field solutions are given with Green's function method. Finally, the results from the method used here are compared with those from the integral equations method. It is verified that the new method used here is feasible.

The approximate analysis of differential systems by applying the theory of regional analysis, is described. It supplies a formularization and calculating programme for algebraic limit cycle of second degree in a type of differential systems of third degree, and also for critical value of damping resistance in power systems. This new method simplifies the traditional method, hence it is acceptable and applicable for engineers. Finally, a few of examples are given based on this method.

In this paper We calculated numerically the electron energy deposition in the cylindrical Ar/Kr/F₂ mixtures Pumped transversely by electron-beam, using SANDYL code, Obtained the relations between energy deposition efficiency and total Pressure of the mixture, electron energy and mixture Composition ratio. Moreover, We made rough estimation of the energy deposition efficiencies of electron and proton by using the formula of the stopping power, and made the comparison of electron and Proton energy losses for the theorical simulation of Proton-beam Pumping.