A direct numerical simulation of transition phenomena in a mixed convection channel flow

This study intends to provide an increased understanding of the laminar-turbulent transition phenomena for the buoyancy-assisted heated vertical channel flow during the early transient stage. The spectral method with weak formulation is applied in the direct numerical simulation. Initial disturbances consist of the finite-amplitude two-dimensional TS wave and a pair of three-dimensional oblique waves for the K-type disturbances. The results from the harmonic energy competitions of different wave modes show that for the buoyancy-assisted heated flow, the (k_x=1, k_z=1) or (1,1) and (1,0) modes would gain energy immediately and start to rise at almost the same rate. This phenomenon is different from that of the buoyancy-opposed flow, where the (1,1) mode decays slowly in the beginning until other modes gain enough energy and then it begins to grow quickly and overtakes the (1,0) mode after a short time period. These different transition patterns match with the experimental results that the flow transition is supercritical and subcritical for the buoyancy-assisted and -opposed flows, respectively. Buoyancy-assisted heated flow transition follows the general trend of an isothermal flow in the beginning, but the thermal-buoyant force is crucial in accelerating the instability and also causing notable differences during the subsequent transition process. All of the results for the vortex structures development, kinetic energy budget of the disturbances, flow visualization by tagged fluid particles, and the local temperature fluctuations are consistent in pointing to a clear pattern for the buoyancy-assisted heated flow transition.     

VRDS装置常压分馏塔系统的问题分析

胜利炼油厂重油加氢 (VRDS)装置的常压分馏塔为填料塔 ,2 0 0 1年检修开工后该系统出现异常 ,经过查找分析 ,确定轻烃 /产品减压渣油换热器和柴油汽提塔重沸器内漏是装置异常的主要原因     

The experimental determination of the neutron cross section for selected solvents

An experiment was conducted in order to determine the macroscopic neutron cross section of various solvents useful in neutron radiographic inspection. These solvents are used to dissolve the salts of high cross-section elements in order to formulate a fluid of maximal neutron cross section. The resulting fluid could then be used as a contrast enhancing agent in neutron radiographic inspection. This experiment was planned using statistical experimental design techniques. The results of this experiment provided a quantitative measure of the mean and standard deviation of the macroscopic neutron cross section for the nine fluids investigated. A control fluid was found to be in close agreement with published values.     

河道冲刷和清水水流河床冲刷率

在冲积河流里。水流条件变化如洪水、水库泄放清水、河道渠化等使挟沙力不饱和引起冲刷，称为河道冲刷。这与水工建筑造成的局部冲刷不同。河道冲刷深度主要决定于冲刷率和冲刷历时。本研究通过对各种泥沙大量实验，证明了河床冲刷率正比于水流提供的冲刷功率并依赖于泥沙粒径和容重，首次提出了冲刷率公式。经验证，该公式可以用于非恒定流输沙和河流洪水冲刷计算。     

光接入网中DWMT调制技术的研究

研究了光纤－电缆调制解调器接入技术的上行信道调制方式，分析了离散小波多音（DWMT）调制与其它调制方式相比所具有的特点和优势，提出了DWMT调制解调器的实现模型，设计了使用DWMT调制解调器的光纤－电缆调制解调器双向传输的系统方案；并对DWMT调制的系统特性进行了计算机仿真分析。仿真结果表明，DWMT调制是一项能有效实用于光纤－电缆调制解调器系统上行信道的技术。     

厚断面球铁的声速

论述了影响厚断面球铁声速和声波衰减的各种因素。指出，必须在应力状态下同时考核声速和声波衰减，以作为判别厚断面球铁材质的一种手段。     

配极变换及其在求解锥面截交线中的应用

本文应用配极变换的几何性质来确定锥面截交线的中心及其主要轴线，这对于准确地绘制或使用数控绘图机来绘制二次曲线．是很有意义的．     

Nonlinear adaptive algorithms for equalisation in mobile satellite communications

This paper considers the equalisation problem in Quadrature Phase-Shift Keying (QPSK) modulated signals which have been distorted by the passage through a transmission channel. The channel is modelled as a Rician fading channel to simulate the behaviour of the transmission channel in the mobile satellite context. The equalisation is treated as the generalisation of the channel behaviour, and some algorithms with the structure of an artificial neural network using the Multilayer Perceptron, Volterra Series and Radial Basis Function are described. Results for the BER performance of typical transversal equalisers, with Square-Root Kalman adaptation algorithm, and algorithms with artificial neural network structure are also reported and evaluated. Improved performance is exhibited by the artificial neural network approaches.     

RAID的存储信道分析

本文从冗余磁盘阵列的信道模型出发，研究各部分组成的理论与技术。文中在给出系统的模型描述之后，着重分析了冗余信息元生与检纠错、数据分割与同步。还研究了系统中的负荷平衡问题，指出了磁盘优化调度的方向。     

复杂目标近场电磁散射的可视化计算方法

首次介绍了复杂目标近场散射计算的可视化方法。采用非均匀有理Ｂ样条曲面（ＮＵＲＢＳ）精确构造任意形状散射体，结合几何体近场透视变换和Ｚ－Ｂｕｆｆｅｒ技术实现了基于Ｗｉｎｄｏｗｓ平台的近场散射计算。提出广义雷达散射截面的概念并给出的若干算例。该方法充分利用了计算机３Ｄ图形设备的几何运算能力，运算速度快，严谨高，可扩展性好。