Detailed modeling and massive tallying of nuclear reactors lead to memory overload for a single core processor.It could not be calculated by Monte Carlo particle transport with particle parallelism only.Domain decomposition is one of solutions.Domain decomposition needs to interchange particles between processors, so that inherit technique of pseudo-random number could not make identical results between serial and parallel.Two techniques of pseudo-random number are described to obtain identical results on different numbers of domains in a Monte Carlo particle simulation code.

In order to develop large-scale transport simulation (such as simulation of whole reactor core pin-by-pin problem), we developed a neutron photon coupled transport code JMCT. In this article, developing idea of a auto modeling tool JLAMT based on field oriented development is introduced. JLAMT developed several quick and assembly modeling tools. Data structure based on hierarchical geometry tree was designed. Automatic conversion and generation of physical model input file for GDML file format are made. By using those modeling tools, complex devices (include DAYAWAN whole-core model) were created, and transformed file was delivered to JMCT for transport calculation. Results were validated for correctness of visual modeling tools.

Mesh tally function of monte Carlo method can give a detailed and intensive calculation of flux distribution in specific volumes. To realize such function in JMCT mesh tally function are designed and realized. It supports non-uniform mesh in three kinds of orthogonal geometry (xyz of rectangular coordinates, rθz of cylindrical coordinates, and rθφ of spherical coordinates). Algorithm for rectangular coordinates is discussed. Calculation on DAYAWAN reactor core pin-by-pin model, Venus benchmark model and a 1-D ITER model verifies preliminarily correctness of JMCT mesh tally. Furthermore, U-array benchmark model is used to test serial performance of JMCT mesh tally. Both JMCT and MCNP5 use same xyz mesh grids and run under same condition. It shows that JMCT takes less time consuming and has higher performance dealing with xyz geometry.

Structure evolution and nature of defects in bcc iron by displacement cascade are investigated with molecular dynamics simulation.Under irradiation displacement cascade induces temporarily self-interstitials,vacancies,<100>, <110>, and <111> dumbbell defects,and composite defects as well,such as,composite defect of <110> and <111> dumbbell defects.composite defect of <110> and dumbbell defects,and defect clusters.Numerical results show that a higher PKA energy might induce more SIAs.The region where atoms are displaced by displacement cascade is about 11-15a₀ in size.A smaller PKA energy gives rise to a smaller region of displacement cascade.At initial stage of 0-0-0.75 ps in displacement cascade,recombination of self-interstitial atoms and vacancies is found.

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.

A multi-dimensional particle-in-cell code KLAP is introduced. Field ionization, impact ionization and two body collision are considered in a one-dimensional code. Moving window technology is used in a three-dimensional code to study laser wakefield acceleration in GeV region. Terahertz radiation, laser propagation in neutral gas medium, surface electron acceleration as well as GeV electron generation in laser wakefield acceleration are studied.

A charge-conserving current assignment algorithm based on current conservation equation proposed by Villasenor and Buneman is introduced.It is found that the algorithm is not available as particle boundary conditions are adopted. With typical boundary conditions amendment methods are proposed in which the simulation satifies charge conservation.

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.

Based on the close relationship between Hamilton-Jacobi (H-J) equations and hyperbolic conservation laws,a high-order numerical method is developed to solve the H-J equations in the 3rd order and 5th order compact schemes.The upwind compact schemes are tested on a variety of one-dimensional and two-dimensional problems,including a problem related to the Richtmyer-Meshkov instability accelerated by planar shocks.Numerical results show that these schemes yield uniform high-order accuracy in smooth regions and satisfactorily resolve discontinuities in the derivatives.Moreover,since the present methods have less numerical dissipation than WENO scheme with the same order,they could be used to solve the H-J equations more accurately in the simulation of multi-scale complex flows.

A three dimensional object oriented parallel particle simulation code PLASIM3D (using the first three letters of the words "plasma" and "simulator") is developed with the purpose of studying the interaction of laser and plasma. The arithmetic of the code is introduced and its performance is tested and analyzed. The linear speedup is acquired in the present test.

A 2(1/2) dimensional particle simulation code PLASIM (Plasma and Simulator) is developed with the purpose of studying the interaction of laser and plasma.The algorithm of the code is introduced.A main characteristics of the code is that it can simulate collision effects by adopting β-particle cloud.Another characteristics is that electrons and ions are both relativistic. So the computation results are more believable when incident laser is ultra-intense.

Through examples, the mechanism of the generation of the aliasing error associated with upwind compact difference schemes and spectral method is studied and compared. The comparison shows the upwind compact difference schemes have some advantages in treating the aliasing error.

An approach combining the fifth Upwind Compact Difference Scheme and Group Velocity Control is applied to simulate directly the interaction of shocks and the density stratified interface of light-gas cylinder.Some research about the generation and development of vorticity and the distortion of edge of cylinder is done.The instability of cylinder density-interface is analyzed.Main character of the linear developing phase is that the gas of higher density goes into the one of lower denstiy at a constant velocity and the spike structure is formed and the character of the nonlinear developing phase is that a pair of vortex structures rotating adversely are formed on both sides of the top of the spike.The numerical solution accords with the experiment.

The temporal spatial discrete Fourier transformation is employed to analyze the dissipation and dispersion errors of the numerical algorithm used here. Based on directly solving the two dimensional time dependent compressible Navier Stokes equations, the spatial evolution of primary vortex generated in forced compressible plane free shear layers is simulated numerically by using a new fifth order upwind compact difference scheme. The phenomena, including the primary vortex saturating, the first pairing, and the second pairing, are shown with the passively conserved scalar method and so on. The initial value effect related to subharmonic disturbances in incoming flows is studied. The results show that the spatial evolution type of large scale compressible vortices is associated with the disturbance modes.

The 3-D Fast Multipole Method, a kind of gridless particle simulation method, is described and improved to obtain higher accuracy. A spherical particle with reduced dimensional motion model is presented. As examples, the spatial distribution of the potential in dust plasma and the instability produced by electrons streaming through ions are simulated. The results of simulations are in agreement with the theory.

An algorithm is proposed to combine Kirchhoff integral and an unsteady flow computation. Axisymmetric jet flows are given by DNS using 5-order accurate upwind compact scheme and 3-order accurate Runge-Kutta scheme. Kirchhoff integral is used to predict the far-field sound. Numerical results show that far-field sound pressure has the directivity and reaches maximal value at 20° diverged from the flow direction. The directivity is attenuating while the propagation distance is increasing.

The linear instabilities in compressible shear layers are investigated by solving the two and three dimensional time dependent compressible Navier Stokes equations.A high accuracy upwind/symmetric compact difference hybrid algorithm is used.A pseudo random number generation technique is employed to simulate the white noise disturbance.Based on numerically solving the three-dimensional viscous disturbance equations by using a new method named as SCD-MNR,some results related to linear stability analysis are first given.Both two-and three-dimensional waves are considered.Compressibility effect can increase the most unstable wave angles besides that damps the growth rates of unstable waves.Numerical results confirm the prediction of linear theory that during the initial evolution of the compressible shear layer unstable waves are linear,and that in this course the wave number and angle of the most unstable disturbance are selective.The algorithm used here appears to be effective.It is a reasonable means for the study on compressible shear layers that linear theory combines with numerical simulation.

The flow fields of 2-D compressible axisymmetric jet are simulated by solving N-S equations. The discretization method has high order accuracy. The information and development of the large vortical structure and it's role in the jet development are studied. The Kelvin-Helmholtz wave appears firstly when jet losts it's stability, and then the single vortex rolls up. After that, with the development of jet, the vortex structures begin to pair and merge because of the increasement of non-linear effects. It is also shown that the pressure distribution is directly relative to the large vortical structures.

Based on the Fourier analysis method, a fully-discretized dispersion relation is derived for a family of high accuracy upwind compact difference schemes by considering one dimensional linear convetion equation temporally discretized by the explicit multi-step Runge-Kutta algorithm. The effects of CFL numbers on the characteristics of these schemes, including dissipation and dispersion errors, phase velocity and group velocity, are analyzed. The two-dimensional anisotropy problem is discussed. Moreover, an eigenvalue analysis is performed. Two numerical examples are used to show the high accuracy and resolution of these schemes.

A high order accurate finite difference scheme is proposed in light of the upwind compact method^[1].The flux vectors in Euler equations are approximated by using upwind compact difference.In order to prevent the nonphysical oscillations in the vicinity of the shock the group velocity control(GVC)method is used.The reason of oscillation production in numerical solutions is nonuniformity of group velocity of wave packets.GVC is for improvement of the shock resolution.The present scheme has third order accruracy in smooth regions.

The stability of temporally evolving compressible plane mixing layers is investigated numerically by solving the three dimensional compressible linear disturbance equations.A high order finite difference method is used.The effects of key parameters such as convective Mach number and Reynolds number on the stability characteristics of compressible mixing layers are analyzed.The comparsions between two and three dimensional,viscous and inviscid disturbances are presented.Part of the numerical results obtained here are in agreement with those of relative literature.

Inorder to simulate multiscale physical problems constructing high order accurate difference schemes is needed. The fourth order accurate compact scheme is reconstructed using the method of diffusion analogy developed by authors in order to make the scheme dissipative. The modified compact scheme with fourth order accuracy in space and third order accuracy in time is used to compute the 2-D shock reflection problems. The computed results show the scheme developod to correctly simulate multiscaler physical problems also can be used to capture the shock well.

In this paper, we present a modified implicit ENO scheme and combine it with CSCM-like implicit supra-characteristic boundary treatment. Numencal experiment with this scheme for 2-D channel fupersonic flow aboat 4% circular arc has damenstrated the sharp shock-capturing capability of the scheme. The results are also compared with those of TVD scheme. The futher application to the viscid flow in simplified inlet is made. They show a good agreelment with the results of SIP/Beam-warming schemes except nearby the reflection point of shock. But our results seem to be more reasonable.

A upwind compact scheme with dispersion regulator is developed and discussed. The scheme developed is dissipative and the dispersion term in the truncation error can be controlled. According to the behaviour of the flow parameters near the shock the scheme with specially chosen control function gives high resolution. The scheme is simple, efficient and the shock can be captured well. The scheme is used to compute the shock reflection problem, and the computed results are satisfactory.

Near wake flow is simulated by using numerical method for solving the Navier-Stokes Equations.In order to get fine solutions near the corner coordinate transformation is made in both x and y directions.The differetial equations are approximared with factored implicit scheme developed in⁽¹⁾. The scheme is implicit, and large time step can be used. But the difference solutions can be expressed explicitly. In process of solution there are no numerical inversions of matrices and no matrix operations.The scheme has advantages of both implicit and explicit schemes.Flows with different Mach number M and Peynolds number Pe are computed.

A new implicit factored difference scheme for solving compressible Navier-Stokes equations on the base of the single step scheme developed before is described in this paper. For the inviscid portion of the Navier-stokes equations the flux vectors are split according to the sign of the eigenvalues of the Jacobian matrices using the property that the nonlinear flux vectors are homogeneous functions of degree one. For the viscous portion correction with operator the addition is used for improving convergence rate. Obtained difference scheme is used to solve Couette flow.