Lattice Boltzmann method is used to simulate natural convection in a cavity fill with porous medium under REV scale. Effects of Rayleigh number, Darcy number and porosity on heat transfer and flow in a square enclosure were studied. It is found that Darcy number has a great influence on fluid flow pattern in the cavity. Increasing Rayleigh number,Darcy number, and porosity enhance the heat dissipation effect. Effect of porosity on average Nusselt number is related to Darcy number. As Darcy number is small, porosity has little effect on average Nusselt number. As Darcy number is great, porosity has a great influence on average Nusselt number. As cold source is placed above the wall, average Nusselt number changes dramatically with the increase of Rayleigh number. Under high Rayleigh number condition, cooling effect is improved by arranging the cold source above the boundory.Among the six schemes, Case 6 has the best heat dissipation effect.

Flow and heat transfer characteristics of a droplet impact onto a relatively high temperature thin film during distillation was studied by means of front tracking method. The proposed model was validated by numerical results with analytical solutions. Evolution of gas-liquid interface and heat flux distribution were investigated. Meanwhile, effect of Weber number and dimensionless liquid film thickness on heat transfer was analyzed. It indicates that according to heat flux distribution after impact liquid film can be classified into three zones: The impact zone, the transition zone and the static zone. Forced convection is the main heat transfer mechanism inside the impact zone mainly due to impact. Increasing Weber number or decreasing dimensionless film thickness could enhance heat transfer. With the increase of Weber number, disturbance caused by impact on liquid film strengthens, which makes synergy of momentum and energy more obvious, thus increasing average heat flux between liquid and solid wall, and coronal spray in the impact zone becomes more obvious. The smaller the dimensionless liquid film thickness is, the greater the average heat flux density is, and the longer the heat transfer duration of high heat flux density is.

An improved LB pseudo-potential multi-relaxation multiphase model is used to study flow characteristics of single/dual droplets impacting liquid film. Development of liquid film impacted by a single droplet under different gas-liquid density ratio was investigated. It was found that with decrease of density ratio, top of coronal crown started bending inward, and bottom radius is significantly reduced. Then, double droplets impinging on liquid film was studied with large density ratio. It shows that a central jet was generated as double droplets impacting on liquid film. Increase of horizontal spacing between droplets delaied the appearance of central jet and reduced height of the initial central jet. With the increase of Re, height of the central jet increased obviously.

Kelvin-Helmholtz instability of two-dimensional immiscible incompressible fluid in a sloping tube was numerically simulated with front tracking method. Effects of inclined angles of wall, thickness of velocity gradient layer and Richardson number on development of K-H instability were investigated. It shows that the greater the angle of wall inclination is, the faster the K-H instability develops and the more liquid is rolled up. It was also found that increase of thickness of the velocity gradient layer under the inclined wall presented an inhibitory effect on roll-up of the interface. The greater gravity items of Richardson number is, the slower the interface rolls up. However, surface tension items of Richardson number have weak effect on the growth of interface.

Direct numerical simulation of FTM (Front Tracking Method) was used to study free rising motion of single bubble in a tube with fins in gravity. Ratio of fin height and pitch to tube length of a side are chosen as geometric characteristics. Morton number is used as characteristic parameter of fluid. With analysis on free rising motion of bubbles at different fin height, pitch and Morton number effects of geometric characteristics of tube and parameters of fluid on motion trajectory of bubbles are studied. It shows that under effect of fins bubble shape is asymmetry and bubbles have lateral displacement like a "snake".This phenomenon is associated with geometric structure of fin and fluid around bubble. The higher fin height is, the more obvious phenomenon becomes. The smaller the viscosity of fluid around bubble is, the greater the horizontal displacement is.

Natural convection heat transfer in a porous medium with partially thermally active walls is studied with lattice Boltzmann method. Convective flow heat transfer with different heating and cooling zones, porosity, Darcy number and Rayleigh number is investigated. It reveals that at Da=10^-4 a circulating flow pattern at the middle of the cavity is found, and porosity have great influence on heat transfer at large Rayleigh numbers; As Darcy number is increased to 10^-2, streamlines exhibit a flow pattern with two vortices, and porosity have great influence on heat transfer at low Rayleigh numbers. Location of partially thermally active walls has significant influence on flow pattern and heat transfer in cavity. Bottom-top with bottom heating and top cooling provides a greater heat transfer rate compared with other partial heating. It is better than fully heated wall of cavity.

To study interpenetrating network hydrogel system of PAM/PVA, molecular dynamics simulation is made to investigate molecular interaction inside a hydrogel system. Effects of water content on PAM/PVA composite hydrogel performance are studied. It is found that cohesive energy density and binding energy of hydrogel system increase with water content increasing. Meanwhile elastic coefficients, engineering modulus and ductility decreased with increasing of water content. In addition, with analysis of pair correlation function, we found that there are mainly hydrogen bonding interactions between H₂O molecules and surrounding atoms or functional groups. Strengths of hydrogen bonds formed are O_water >O_PVA >O_PAM >N_PAM, which consists with possibility (difficulty) of forming hydrogen bond.

Based on the cluster multiple labeling technique,a novel cluster detection algorithm is presented as an analysis subroutine in two-and three-dimensional molecular dynamic simulations of ejecta that take place as a planar shock wave encounters a free metal surface.The algorithm is described,tested,and used to detect cluster distribution of ejecta from copper and aluminum under a shock loading.The information obtained about the size,distribution,evolution of the cluster is helpful in the understanding of ejection.

An in-core fuel management code package HEX-ICFM is developed for Xi'an Pulsed Reactor.The orthogonal design model and the loading pattern optimization program HEX-ORTH are studied.The cell calculation is performed using WIMS-D/4.A two dimensional hexagonal geometry multigroup nodal theory code SIXTUS-2 is used for core diffusion calculation.The core physical parameters are calculated using HEX-ICFM for the first cycle of Xi'an Pulsed Reactor.With the fuel of end of cycle 3 and 30 fresh fuel rods the optimum loading patterns are calculated for the objective function max(K^BOC_eff)using HEX-ORTH.

The spallation target of ADS is studied using the program DCM/CEM.The calculation of standard lead target bombarded with 0.1~1.6GeV proton beams is carried out.The neutron spectra and distribution over the lead target, energy deposition and neutron production in the lead target are studied. The simulation results agree with the former theoretical and experimental results.

The sampling method by coupling criticality source direction biasing and the exponential transform is established for duct shielding calculation.In sample problem studying,the optimal source direction biasing parameter p₁、exponential transform parameter p₂ are supposed and the variance of duct calculating results by using this method is shown to reduce efficiently.Correction calculation for the duct of Nuclear Power Institute of China (NPIC) pulsed reactor shows the results are more close to the measured ones.

A semi-analytic method is proposed for solving dynamics initial-boundary value problems of one dimension under alternate force.It adopts differential quadrature method in space domain and series in time domain on the basis of controling partial differential equation,and gets DQ linear equations for solving all parameters of the displacement-field by adding timepoints.