Perfectly matched layer (PML) absorbing boundary conditions (ABC) are presented for nonlinear Euler equations in unbounded domains. The basic idea consists of two steps. First,PML technique is applied to linearized Euler equations in either a uniform mean flow or a parallel mean flow. Nonlinear PML equations are then derived by replacing flux functions in linearized Euler equations with nonlinear counterparts. Since a stiff source term gets involved in PML equations,an implicit-explicit Runge-Kutta scheme is proposed to integrate discrete ODE system. Numerical experiments are performed. They demonstrate advantage of proposed PML ABC over traditional characteristic boundary condition.

Multiplication-reactivity conversion factor is a key parameter in CFBR-Ⅱ to get reactivity at subcriticality by neutron source multiplication method.It was measured in many experiments,but the results were different.In order to explain this,we derive an expression of multiplication-reactivity conversion factor with transport equation.Aimed at CFBR-Ⅱ,multiplication-reactivity conversion factor in different reactivity states are calculated with Monte Carlo Method.It is concluded that multiplication-reactivity conversion factor is determined by delayed neutron fraction,importance ratio of external neutron source and fission neutron source,neutron leakage probability ratio of multiplication system and substitute system,detector efficiency ratio of multiplication system and substitute system.Multiplication-reactivity conversion factor varies with CFBR-Ⅱ's reactivity.

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.

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.

Lindman boundary condition is adopted in particle simulation code LARED-P. Using this code, obliquely incident laser propagation in plasma is numerically studied, with enough testing computation, it is convinced that Lindman BC can officiently diminish wave reflection into simulation area.

A two-dimensional relativistic electromagnetic particle simulation code (2DCIC) is presented. The charge and current densities are computed self-consistently using Maxwell's equations, relativistic motion equations of electrons and Newton's equations of ions by tracking 10⁴-10⁶ simulated particles. some details of wave wave and wave particle interaction are also studied together with the evolution of instability as time. Laser light impinges obliquely (or normally) on plasma, which has a density gradient (or homogeneous density). To save computational time, the parallel computational method is developed. Using this code, the ultrashort intense pulse laser plasma interaction and other plasma problems can be also studied by modifying parameters of physical model. After a lot of test computation, plasma equilibrium and propagation of ultrashort intense pulse laser in plasma are studied. The computed physical picture is reasonable.