For numerical simulation of spontaneous fission neutron source energy, neutron multiplicity and neutron angular correlation distribution, a NESF numerical simulation program is developed to provide fission neutron multiplicity, energy, angular distribution and other parameters on basis of fission process. The program is integrated into existing neutron transport software. This report focuses on background, physical basis, and process of the program, as well as numerical simulation correlated to neutron angular correlation distribution characteristics and nuclear component characteristics.

Based on E-H TDFEM method derived directly from Maxwell's curl equations, Crank-Nicolson difference scheme is implemented for time-partial differential equation to obtain an unconditionally stable algorithm. Curvilinear tetrahedral elements are applied to discretize computational domain and electric and magnetic fields are expanded with same hierarchical vector basis functions. A sphere cavity and a cylindrical cavity partially filled with dielectric rod are simulated. It shows that curvilinear tetrahedral elements can reach higher accuracy with same mesh numbers, compared with tetrahedral elements. Better results can be obtained by curvilinear tetrahedral elements combined with 1.0 order hierarchical basis functions with fewer unknowns than that combined with 0.5 order hierarchical basis functions.

We set up a numerical experiment platform.It consolidates codes used to simulate warhead verification technologies of passive neutron,passive γ ray,active neutron,active high-energy photon and delayed neutron methods.Two functions on simulating time-dependent coincidence and neutron multiplicity counter measurements were added to the platform.They are carried out by DTB code and NMC code.This paper introduces development and validation of the programs,including theory and program flow.Two numerical experiments are designed to validate the program.The platform provides systematic data to support statistical analysis on nuclear warhead verification technologies

To analyze force of fluid on a rigid object near free surface,a mathematical model with free surface effect is developed based on potential flow theory.It is calculated with boundary element method.Nonlinear kinematic and dynamic boundary conditions are taken into consideration.With control equation and boundary conditions,piercing cylinder through free surface and phenomena of spike are simulated.A comparison between numerical and experimental results shows that the method is appropriate.Pressure on moving objects,transform of free surface,resultant hydrodynamic force and velocity of flow field are analyzed in detail.It shows that the nonlinear method with free surface effect predicts precisely force on moving objects in vicinity of free surface.

Locally conformal perfectly matched layer (PML) is extended to a high order FEM combined with curvilinear elements and high order basis functions, which proves accuracy and efficiency. It is able to handle challenging geometries with arbitrary curvatures with few unknown numbers, especially those with curvature discontinuities. Validity of the proposed method is demonstrated.

Finite element tearing and interconnecting method(FETI) is used in analyzing electromagnetic scattering of complex medium.It decomposes computational space and complex medium.With reasonable operations of algebra,a 3D problem is changed to a 2D problem.It reduces computational complexity.By using Krylov solver,computation of reverse matrix is avoid in the equation about interface system.Numerical results show that the method is accurate and efficient for electromagnetic scattering of complex medium.

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.

We study adaptive computation of drag-coefficient of flow around a cylinder. We adopt upwind finite element schemes for two-dimensional stationary viscous incompressible Navier-Stokes equations, derive weighted posteriori error estimation for drag-coefficient by introducing a dual problem, and implement adaptive mesh refinement. Numerical examples show feasibility of the scheme and robust performance of estimators.

Based on the simulation of the M₂ tide in the Bohai,Yellow and East China Seas,numerical experiments are made to study 4 strategies on the bottom friction coefficient(BFC) in a numerical adjoint model.In order to make a better simulation,the strategy must be consistent with the given BFC distribution.The real bottom friction decided by ocean topography is very complicated and an independent BFC is required.The fourth method which takes the BFC in each grid point as an independent BFC simulates practical experiments best and demonstrates the reasonability and efficiency of this method.

Gaseous detonation propagation through a bifurcated tube was numerically investigated. A 2^nd additive semi-implicit Runge-Kutta method and a 5^th order WENO scheme were used to solve two-dimensional reactive Euler equations. A detailed chemical reaction model was utilized to describe the heat release of detonation. The contours of density, pressure, temperature, species OH mass fraction, the computed cellular pattern and the traveling speed of detonation were obtained. The results show that, influenced by the rarefaction waves from the left sharp comer, the reaction zone is separated from the leading shock. Then, the detonation is degenerated into the deflagration. The winkled reaction front can be clearly identified in numerical schlieren and temperature contours. Re-initiation is induced by the leading shock reflection on the right wall in the vertical branch. Mach reflection of disturbed detonation occurs in both vertical and horizontal branches. The boundary between regions of uniform and larger cells is not a straight line; it doesn't exactly start at the left sharp comer and is usually upstream of the left sharp comer. The triple-point trajectory characterizing Mach reflection locates downstream of the right comer in the horizontal branch. Complex structures of vortices, the unreacted region, and shock-vortex interaction are observed in flow field around the left comer. Vortices accelerate reaction rates of the unreacted region. The reflected shock interacts with vortices and breaks them into pieces. Reflected shock also accelerates the consumption of the unreacted region and then an embedded jet is produced. The evolution of detonation wave and computed cellular pattern are qualitatively consistent with those from experiments.

The key step for reliability assessment with small sampling is to take advantage of the subjective information and the test data of input parameters. Subjective inference could just offer the reliability some incomplete information which can be generally assumed to exist in the form of either a prior mean or a prior credibility interval. To the trials with the outcomes of either survival-failure or normal distributed parameters, efficient approaches are developed to determine the conjugate prior distributions from the subjective information according to the principle of maximum entropy. The test data of input parameters are also transformed as the prior information of the output parameters according to statistics theory. Bayes theorem is used to synthesize the different informations and numerical examples are presented to illustrate the impact of non-experimental information on the reliability posterior, the needed test number and the reliability assessment.

In this paper a mathematical model for temperature field in deep underground unsteady is developed. We have to deal with two coupled convective-diffusion equations in three dimensional space and we propose a reduced equation, which is a single integro-differential equation, of the coupled system.In order to reduce greatly both the memory requirements and the computational effort, for its numerical approximation our particular concern will be in the treatment of the integral term. We also show some numerical examples.