The distribution characteristics of the neutron field in cement was simulated using the MCNP code to comply with the requirements of an online Prompt Gamma Neutron Activation Analysis system.Simulation results showed ...The distribution characteristics of the neutron field in cement was simulated using the MCNP code to comply with the requirements of an online Prompt Gamma Neutron Activation Analysis system.Simulation results showed that the neutron relative flux proportion reduced with increasing cement thickness.When the cement thickness remains unchanged,the reduced proportion of thermal neutrons increases to a small extent,but the epithermal, intermediate,and fast neutrons will decrease according to the geometric progression.H element in the cement mainly affects the reduction of fast neutrons and other single-substance elements,e.g.,O,Ca,56Fe,Si,and Al.It also slows down the reduction of the fast neutrons via inelastic scattering.O contributes more than other elements in the reduction of fast neutrons.Changing the H content affects the thermal,epithermal,intermediate,and fast neutrons, while changing the Ca,Fe,and Si contents only influences the thermal,epithermal,and intermediate neutrons;hence, there is little effect on the reduction of fast neutrons.展开更多
For solving higher dimensional diffusion equations with an inhomogeneous diffusion coefficient,Monte Carlo（MC） techniques are considered to be more effective than other algorithms, such as finite element method or f...For solving higher dimensional diffusion equations with an inhomogeneous diffusion coefficient,Monte Carlo（MC） techniques are considered to be more effective than other algorithms, such as finite element method or finite difference method. The inhomogeneity of diffusion coefficient strongly limits the use of different numerical techniques. For better convergence, methods with higher orders have been kept forward to allow MC codes with large step size. The main focus of this work is to look for operators that can produce converging results for large step sizes. As a first step, our comparative analysis has been applied to a general stochastic problem.Subsequently, our formulization is applied to the problem of pitch angle scattering resulting from Coulomb collisions of charge particles in the toroidal devices.展开更多
对白噪声驱动随机系统的Fokker-Planck方程进行约化,求得约化方程的解析解,使用局部解析解和 Monte Carlo结合方法求解常系数Fokker-Planck方程,并与常系数Eokker-Planck方程的精确解进行对比, 之后求解了变驱动力系统的行为．数值模拟...对白噪声驱动随机系统的Fokker-Planck方程进行约化,求得约化方程的解析解,使用局部解析解和 Monte Carlo结合方法求解常系数Fokker-Planck方程,并与常系数Eokker-Planck方程的精确解进行对比, 之后求解了变驱动力系统的行为．数值模拟结果表明,有限解析／Monte Carlo结合的方法,能成功求解-维 Fokker-Planck方程,求解粒子数为105个,能获得十分光滑的PDF分布曲线,计算颗粒在300个时,就能获得较好的均值．其研究为两相湍流PDF模型新计算方法研究提供基础．展开更多
To mitigate the damages produced by flood discharges of hydropower stations, a three-dimensional numerical model of the aerated water jet restricted by gravity, air resistance and air buoyancy is proposed. Based on th...To mitigate the damages produced by flood discharges of hydropower stations, a three-dimensional numerical model of the aerated water jet restricted by gravity, air resistance and air buoyancy is proposed. Based on theoretical analysis and prototype data, a three-dimensional stochastic model is constructed using Monte Carlo method to evaluate the range of atomization and intensity of rainfall in gorges, which are strongly affected by complex terrain and various wind conditions. The prototype data observed from two hydropower stations are selected in the feedback and verification analysis to verify the proposed model. The result shows that the computational solutions fit the prototype data well. This model can be used to forecast the atomization of a hydropower station that is being designed or constructed.展开更多
基金Supported by National Natural Science Foundation for Distinguished Young Scholar(41025015)NSFC(40974065,11105132)+3 种基金Province Key Technology R&D Program(2011FZ0055)National High Technology Research and Development Program of China(2012AA063501)the Basic Research for Application of Sichuan Province(2012JY0109)China Postdoctoral Science Foundation(2012M520245)
文摘The distribution characteristics of the neutron field in cement was simulated using the MCNP code to comply with the requirements of an online Prompt Gamma Neutron Activation Analysis system.Simulation results showed that the neutron relative flux proportion reduced with increasing cement thickness.When the cement thickness remains unchanged,the reduced proportion of thermal neutrons increases to a small extent,but the epithermal, intermediate,and fast neutrons will decrease according to the geometric progression.H element in the cement mainly affects the reduction of fast neutrons and other single-substance elements,e.g.,O,Ca,56Fe,Si,and Al.It also slows down the reduction of the fast neutrons via inelastic scattering.O contributes more than other elements in the reduction of fast neutrons.Changing the H content affects the thermal,epithermal,intermediate,and fast neutrons, while changing the Ca,Fe,and Si contents only influences the thermal,epithermal,and intermediate neutrons;hence, there is little effect on the reduction of fast neutrons.
基金supported in part by the Higher Education Commission of Pakistan under PPCR programsupported by the National Magnetic Confinement Fusion Program under Grant No.2013GB104004Fundamental Research Fund for Chinese Central Universities
文摘For solving higher dimensional diffusion equations with an inhomogeneous diffusion coefficient,Monte Carlo（MC） techniques are considered to be more effective than other algorithms, such as finite element method or finite difference method. The inhomogeneity of diffusion coefficient strongly limits the use of different numerical techniques. For better convergence, methods with higher orders have been kept forward to allow MC codes with large step size. The main focus of this work is to look for operators that can produce converging results for large step sizes. As a first step, our comparative analysis has been applied to a general stochastic problem.Subsequently, our formulization is applied to the problem of pitch angle scattering resulting from Coulomb collisions of charge particles in the toroidal devices.
基金Supported by Natural Science Foundation of China (No.50379033)Program for New Century Excellent Talents in University.
文摘To mitigate the damages produced by flood discharges of hydropower stations, a three-dimensional numerical model of the aerated water jet restricted by gravity, air resistance and air buoyancy is proposed. Based on theoretical analysis and prototype data, a three-dimensional stochastic model is constructed using Monte Carlo method to evaluate the range of atomization and intensity of rainfall in gorges, which are strongly affected by complex terrain and various wind conditions. The prototype data observed from two hydropower stations are selected in the feedback and verification analysis to verify the proposed model. The result shows that the computational solutions fit the prototype data well. This model can be used to forecast the atomization of a hydropower station that is being designed or constructed.
