By combining advantages of S_N method (high calculational efficiency) and advantages of MC method (fine geometrical modelling), three-dimensional discrete ordinates-Monte Carlo method (3D S_N-MC coupling method) is able to calculate cavity streaming dose rate in short time. S_N-MC coupling method is applied on Qinshan No.1 reactor and CAP1400 reactor cavity streaming calculation. Results of S_N-MC coupling method are compared with measurements and results of MCNP bootstrapping method. It shows that theoretical model and codes of 3D S_N-MC coupling method are both correct.

Flowfield in a constant area isolator is numerically simulated with coupled double distribution function lattice Boltzmann method(LBM).Numerical results reflect general structure of flow field which means that LBM is a potential computational fluid dynamics method.

Homoclinie intemections are soul.ce of chaos for a map.It is convenient to determine whether a given map iS chaotic or not by computing stable and unstable manifolds of its hyperbolic fixed point and observing if there are homoclinic intersections.A new algorithm is presented to compute one-dimensional stable and unstable manifolds of a map.Inspired by a unique property that derivative is transported along the orbit of one-dimensional manifold.position of new point is located quickly with a two-step "prediction and correction" scheme.Tangent component of the manifold is used as reference line to check if the uew point is acceptable.Performance of the algorithm is demonstrated with several typical chaotic maps.It shows that the algorithm is capable of computing both one- dimensional stable and unstable manifolds of maps.

In order to balance growth rate of manifold in all directions and construct global manifold structure of a dynamical system,a radial control factor is adopted to normalize the original dynamical system.Taking radius component of the tangent vector as a standard,this method controls manifold expanding at same speed in all directions.Theoretical analysis and example calculation demonstrate that manifolds before and after normalization have same orbit with the original one,which means their global manifold structures are consistent.Lorenz and Duffing systems are taken for examples to demonstrate effectiveness of the proposed approach.It indicates that the method not only get same effect as geodesic process but also present manifold in discrete flow way,which avoids many complicated boundary value problems.

With definition of DHT(distinguished hyperbolic trajectory) and existing measure function in phase space,a measure function in extended phase space is presented.Existing algorithms with constant accuracy parameters is laborious as high precision is required.In order to overcome this shortage,a variable-step convergence algorithm is proposed.The main idea is to estimate initial region with the help of ISP(instantaneous stagnation points) and adopt variable-step grids to increase efficiency.With theoretical analysis and numerical calculation,an optimal range of key parameter is given.Two-dimensional and three-dimensional Duffing systems are used to test the performance.It shows that convergence route gained by the developed measure function is smooth and stable.And the variable-step convergence algorithm is more efficient.

With embedding theorem proposed by Takens,we study methods for choosing proper delay time in phase space reconstruction of chaotic time series.A united method to incorporate advantages of average displacement and mutual information is put forward.In mutual information calculation we employ binary tree coding to divide and mark grids which makes it implemented easily.We determine layer numbers according to percentages of sparse grid.Numerical experiments of R ssler and Lorenz systems verifies accaracy of the method.

Numerical simulation on flows and heat transfer of water at supercritical pressures in inclined upward smooth tubes of Φ32 mm×3 mm at an angle of 20° respect to the horizon is made. Length of the tube is 8 000 mm. Influence of violent variation of water properties in the so-called "large specific heat region" on heat transfer characteristics was investigated. Numerical method was validated by comparing numerical results with experimental data. Variation of the inner surface temperature of tube wall with enthalpy of water, mass flow rate and heat flux were obtained at pressures of 26 MPa and 34 MPa, respectively. It was found that distributions of wall temperature, as well as heat flux, along tube wall's circumference were non-uniform. Difference between top generatrix wall temperatures and the bottom generatrix wall temperature was analyzed. Effect of water properties in the so-call "large specific heat region" on heat transfer of water was also discussed. Two parameters, namely cross-section transverse kinetic energy and cross-section relative transverse kinetic energy were introduced to quantitatively describe intensity of secondary flow. And density grads along a cross-section perpendicular bisector were used to analysis secondary flow. Abnormal mechanism of inner wall temperature distribution in a large specific region in inclined upward tubes at supercritical pressures was discussed.