Flow Characteristics of Skimming Flows in Stepped Channels

Skimming flows in stepped channels are systematically investigated under a wide range of channel slopes (5.7°?θ?55°). The flow conditions of skimming flows are classified into two flow regimes, and the hydraulic conditions required to form a quasi-uniform flow are determined. An aerated flow depth of a skimming flow is estimated from the assumption that the residual energy at the end of a stepped channel coincides with the energy at the toe of the jump formed immediately downstream of the stepped channel. In a quasi-uniform flow region, the friction factor of skimming flows is represented by the relative step height and the channel slope. The friction factor for the channel slope of θ=19° appears to have a maximum. The residual energy of skimming flows is formulated for both nonuniform and quasi-uniform flow regions. Further, a hydraulic-design chart for a stepped channel is presented.     

Numerical Simulation of Relatively Wide, Shallow Channels with Erodible Banks

A two-dimensional numerical model was developed to simulate relatively wide, shallow rivers with an erodible bed and banks composed of well-sorted, sandy materials. A moving boundary-fitted coordinate system was used to calculate water flow, bed change, and bank erosion. The cubic interpolated pseudoparticle method was used to calculate flow, which introduced little numerical diffusion. The sediment-transport equation for the streamline and transverse transport was used to estimate bed and bank evolution over time, while considering the secondary flow. Bank erosion was simulated when the gradient in the cross-sectional direction of the banks was steeper than the submerged angle of repose because of bed erosion near the banks. The numerical model reproduced the features of central bars well, such as bar growth, channel widening due to divergence of the flow around the bars, scour holes at the lee of the bars, and the increase of bar size with time. These features were in accordance with the observations for laboratory experiments. It also reproduced the features of braided rivers, such as the generation of new channels and abandonment of old channels, the bifurcation and confluence of channels, and the lateral migration of the channels. The model showed that the sediment discharge rate fluctuated with time, one of the dynamic features observed in braided channels.     

IMP 用于热电阻测温的新方法及其输入通道的扩展

英国施伦伯杰公司的数据采集器 IMP,35951B 能用于电阻测温,而35951A 却不能.前者仅有10个通道,后者20个通道,而两者的价格差不多,本文提供一种以35951A 代替35951B 用于热电阻测温的方法可使通道成本降低50%,又提供几种扩展 IMP 输入通道的方法可使工程费用成倍的降低.这些方法对大型计算机监测系统很有价值.     

The effects of technological innovation on sustainable development and environmental degradation: Evidence from China

Despite the rapid progress of the global economy and technology's key role, severe environmental and ecological challenges must be given proper attention to advance sustainable development. This paper uses the autoregressive distributed lag method on 40 years of data to investigate the impact of technological innovation on China's sustainable development and determine the channels through which technological innovation contributes to sustainable development. Our empirical results demonstrate that technological innovation is an important driver in promoting sustainable development, revealing that innovation adds to economic growth without harmful effects on the environment. The results also indicate that financial development significantly adds to China's sustainable development through carbon dioxide (CO₂) emissions reduction, and economic growth further triggers the sustainability process by reducing CO₂ emissions. The findings of this paper enhance existing theories and contribute to the progress of sustainable development in China, the novel results outlining industry development drivers could potentially be used for developing global innovation policies integration.     

Numerical investigation of channel columns with complex stiffeners—part I: test verification

A numerical investigation on fixed-ended cold-formed steel channel columns with complex stiffeners subjected to axial load is described in this paper. The complex stiffeners of the channel sections consist of simple lips with return lips. The specimens were brake-pressed from high strength zinc-coated structural steel sheets having a nominal yield stress of 450 MPa. A non-linear finite element model is developed and verified against experimental results of fixed-ended channel columns with complex stiffeners. Initial geometric imperfections and material non-linearity are included in the model. The calibrated model is shown to provide accurate predictions of the experimental ultimate loads and failure modes of the tested columns.     

基于天线选择的MIMO系统能效功率分配优化

对MIMO系统在毫米波衰落信道下的能效功率分配进行研究,以期实现绿色传输。考虑发送端采用天线选择技术,接收端采用最大比合并技术,给出系统能量效率公式,并构建系统基于能效最大化的目标优化函数。利用拉格朗日乘子法,获得迭代功率分配方案。利用排序法及朗伯函数给出简单的闭式功率分配方案。利用Matlab软件验证所提功率分配方案的有效性。仿真结果表明,文章提出的功率分配方案较穷举搜索法EE性能得到了明显提升,是一种复杂度低的优化算法,能快速收敛到EE最大值。     

论高新技术改造我国矿产资源企业的途径

怎样利用高新技术改造我国传统矿产资源企业，进而实现我国传统矿产资源企业的高新技术化，是知识经济时代在讲求科学的发展观的理念下，对我国传统矿产资源企业实现高效可持续发展的现实要求，而不断探寻运用高新技术改造我国传统矿产资源企业的途径，不失为一种现实而科学的选择。     

Investigation on the Dimensions and Shape of a Submerged Vane for Sediment Management in Alluvial Channels

A submerged vane is a flow-training facility mounted vertically on the channel bed to control the sediment movement in the channel cross section, and has been utilized in various applications, such as prevention of bank erosion, sediment exclusion at water intakes, and deepening channels for navigation. The performance of a submerged vane is related to its dimensions and shape. This study aims to investigate a vane’s sediment control effectiveness as a function of its size and shape, with the expectation of an optimal combination of dimensions and shape. A model for the calculation of the transverse bed profile in a cross section of a straight alluvial channel induced by a single submerged vane is developed. The model is utilized to investigate the performances for three types of vanes: (1) rectangular plates with various height and length; (2) tapered plates with linear decreasing in length from the base to the top; and (3) plates of parallelogram with the top of the plates swept forward or backward. Design guidelines and suggestions on the dimensions and shape of the vane are provided based on the results.     

840D系统在数控双面卧式铣镗床上的应用

介绍了西门子840D系统在数控双面卧式铣镗床上的应用,并具体说明了840D数控系统的双通道、双工作组的控制功能和补偿功能的实现.     

稠密栅元棒束内流动行为的CFD数值模拟

国内针对稠密栅元组件内流体的流动和传热特征展了大量的实验研究,但目前仍缺乏对稠密栅元通道内冷却剂流动特性的全面认识.本文对矩形和三角形稠密栅元通道内的空气湍流流动进行了数值研究.结合实验数据,系统地验证了涡粘性和雷诺应力两类湍流模型模拟稠密栅元内流动特征的适用范围.结果表明:SSG雷诺应力模型对流动有较好的模拟,但在棒壁窄缝处的计算结果与实验数据存在较大的差距;在y+<20时,SSG模型对近壁面区域网格的疏密不敏感;在y+较小时,二阶ω模型出现数值震荡.