To obtain reasonable scales and grid requirements of computational zone, water flow in 5×5 fuel pins assembly was simulated adopting incompressible N-S equations, standard k-ε turbulent model and SIMPLE algorithm. By comparing pressure drop, velocity and its vertical component at different planes perpendicular to fuel pins, with relative error smaller than 5%, conclusions were obtained. Length of inlet part and outlet part of computational domain should be about 2.0 times and 2.3-2.8 times of space between two spacer. Polyhedral mesh should be adopted and its scale should be smaller than 0.35 mm in zone between spacer as smooth pin zone adopt structured grid with 0.3 mm-0.5 mm dimension.

For parallel computation,two techniques are proposed to couple Fourier transform and fluid dynamics.One is muiti-physics coupled communication technique and the other is parallel Fourier transform.By comparing efficiency of the two techniques,it is shown that the muiti-physics coupled communication technique is better than calling parallel FFTW technique as the number of cores is relatively small,while calling parallel FFTW technique is better as the number of cores is over a thousand.Scalability is demonstrated with a parallel efficiency above 50% on 16 384 processors.Numerical simulation on laser filamentation is shown.

We present a method for parallel solution of Poisson's equation on irregular domains,which is a key in solving threedimensional electromagnetic problem of a high power microwave device with complex geometry.Irregular domains are expressed with non-uniform grids,where neighbor grids can not be stored in neighbor positions,thus make parallelization difficultly.In our method,an irregular region is expressed by an uniform grid expression with geometry constraints,and then,a parallel Poisson equation is solved on irregular domains by using red-black reordering method.Numerical results validate effectiveness of the method.We also evaluate irregular domains'effect on parallel performance.

A conservative remapping algorithm based on donor-cell method for multiscale dynamic simulation is proposed which couples micro molecular dynamics (MD) simulation with macro finite element (FE) method. Since physical quantities are obtained with integral reconstruction from information of FE nodes and their underlying MD atoms, the algorithm can be applied to both structured and unstructured meshes. An auxiliary mesh is introduced for vertex-centered unknowns. Accuracy and efficiency of the method are validated with numerical experiments.

A parallel code, with fully three-dimensional nonlinear hydrodynamics coupled with light wave propagation, is implemented to study mechanism of laser beam self-focusing and filamentation instability as high intensity laser propagates in a large size underdense plasma. Numerical method and parallel algorithms are introduced.

With the development of massively parallel processing, it is necessary that the parallel applications would be capable of good scalability. It is described how to use the near optimal scalability analysis method with the two dimensional electromagnetic plasma parallel program using particle in cell method as an example. Having known the performance of small parallel systems, one can obtain the information about how many processors which the larger systems are running on can obtain the more"reasonable" performance when using the near optimal scalability analysis. A suit of practical scalability evaluation method is also proposed to find the reason why the practical scalability is bad, and help to optimize the application programs.

The energy band structure,density of state and Mulliken charge density of the F₃-center in α-Al₂O₃ are studied by an embedded-cluster model,when H-like wave function is used for F-center.The optical transition model of the color center is also discussed.It found one single energy level and one doubly-degenerate energy level in the fundamental gap of the crystal with F₃-center.There is a new transition from defect energy level to conduction band and the transition energy is 3.54 eV.Comparing with the absorption spectrum of α-Al₂O₃ by high-energy and great flux neutron radiation,shows that 0.356 μm(3.483 eV) experimental absorption peak should be due to the F₃-center.Also,it found the charge density is less in the site of F₃-center than that of Fcenter in α-Al₂O₃ crystal.

The electronic structure of rutile TiO₂ crystal with F-type color center is studied by using the H-like wave function and Discrite Variation method with the relaxation of ions around color center,and their energy band,density of states are obtained.The results show that F and F⁺ center have donor energy level in forbidden band,and F²⁺ center has acceptor energy level in forbidden band.The optical transition energy are 0.85 eV and 1.67 eV for F and F⁺ center,respectively.The optical absorption peaks 1.7μm(0.75 eV),760 nm(1.61 eV) in the reduced sample of TiO₂ are due to the F and F⁺ center,and a transferring of F⁺→F existed.

The nearest neighbour relation between cities on random triangle lattice has been used to construct a tour subspace and to solve the traveling salesman problem. With importance sampling simulated annealing method and subtour optimization method, the efficiency has been raised obviously. Near optimal solutions are obtained in shorter computation time.