Discharging capacity of rectangular side weirs in straight open channels

A side weir is a hydraulic control structure used in irrigation and drainage systems and combined sewer systems. A comprehensive laboratory study, including 843 tests for the discharge coefficient of a sharp-crested rectangular side weir in a straight channel, was conducted in a large physical model under subcritical flow conditions. The discharge coefficient is a function of the upstream Froude number, the ratios of weir length to channel width, weir length to flow depth, and weir height to flow depth. An equation was developed considering all dimensional parameters for discharge coefficient of the sharp-crested rectangular side weir. The average error of the proposed equation is 4.54%. The present study data were compared with ten different discharge coefficient equations developed by several researchers. The study also presents water surface profile and surface velocity streamlines.     

ELID镜面磨削技术——砂轮快速修整技术的研究

介绍了ELID磨削中采用电火花整形装置对金属结合剂超硬磨料砂轮进行整形修整的技术。修整后的砂轮径向跳动量小于1μm,砂轮表面光滑,形状精度高,磨粒等高性好,适于精密镜面磨削用,具有修整时间短、成本低、砂轮损耗小的优点。     

模具制造中的高速加工技术

分析了传统电加工工艺在模县制造中存在的主要问题，介绍了超高速加工技术的主要特点，论述了超高速加工用于模具制造的关键技术，列举了一些应用实例和使用效果，指出了超高速加工技术在模县制造中广阔的应用和发展前景。     

Discharge characteristics and structure of flow in labyrinth weirs with a downstream pool

A new design of a labyrinth weir is introduced in this study by adding a square pool to the vertex of a one-cycle triangular labyrinth weir with a sidewall angle of 45°. The addition of the square pool increased weir length without causing an excessive nappe interaction, and as a result, reduced the head water over the weir with the same discharge. Laboratory experiments were carried out to investigate the hydraulic performance of the new design with a potential application in pool-weir fishways. Mean and turbulence characteristics of flow for different weir geometries and in both free and submerged flow regimes were measured to be used for prediction of fish behaviour in the upstream of the proposed weir models. Discharge coefficients based on channel width and weir length were calculated. It was found that the new design can significantly increase the capacity of triangular labyrinth weirs and provide financial advantages in construction over triangular labyrinth weirs without pools in low discharges. In submerged flow conditions, the proposed model performed better than sharp-crested linear weirs in low discharges. Contour plots of the three-dimensional velocity components showed a region of strong mean flow around the neck of the new weir model. Turbulent characteristics such as turbulent kinetic energy, power spectra, exuberance ratio, and joint probability distribution functions of velocity fluctuations were extracted from instantaneous three dimensional velocities for different weir depths and flow regimes. Two vertical planes were identified based on the highest turbulent mixing in free and submerged flow regimes. The depths contributing the most to turbulent mixing were identified; active depths decreased as the flow regime changed from free to submerge flow regime.     

Overflow characteristics of streamlined weirs based on model experimentation

Weirs are a type of hydraulic structures that are used in water supply systems and irrigation networks for different purposes. These structures are categorized as different types and must be selected in respect to the hydraulic conditions to satisfy all the objectives of a project. The present study subjects to investigate the hydraulic characteristics of flow over the streamlined weirs, based on model experimentation. The streamlined weirs are a special type of weirs, designed based on the airfoil theory. These weirs have some merits compared to the other types of weirs. They have high discharge coefficient, more stability and less fluctuations of water free surface. According to the objectives of the present study, an experimental investigation was performed, using different experimental models of the streamlined weirs, designed according to the Joukowsky transform function. Experimental results inferred that for a constant flow discharge, the upstream flow heads over the streamlined weirs with different relative eccentricities are almost constant, showing an approximately constant discharge coefficient by the variation of the relative eccentricities. Furthermore, adding a downstream sloped face does not change the flow discharge coefficient. However, increasing the weir height, results in the increase of the flow head and the decrease of the flow discharge coefficient, especially, for the higher heads and the lower relative eccentricities.     

A novel comprehensive correlation for discharge coefficient of square-edged concentric orifice plate at low Reynolds numbers

Among various differential pressure flow meters, the orifice meter has gained its publicity in applications where cost, space, and ease of maintenance are of high priority. A major problem associated with the use of orifice flow meters at low Reynolds number flows is the significant variation of discharge coefficient (C_d) as a function of orifice geometry and the Reynolds number. In this work, a two-dimensional axisymmetric numerical model was applied to the investigation of viscous, incompressible flow through square-edged concentric orifice plate for the purpose of studying the performance of discharge coefficient consequent to variations of Reynolds number (Re), orifice/pipe diameter ratio (β), and orifice thickness ratio (t*). The analysis of numerical results by means of multiple regression method has yielded a new correlation incorporating the effect of the parameters under study on orifice meter discharge coefficient for orifice bore Reynolds numbers (Re_o) < 250. Results of relevant investigations from the literature are used in the present work as references for the validation of the numerical model as well as the proposed correlation for discharge coefficient.     

Experimental modeling of flumes with two semi-cylinder contractions (free and submerged flows)

In this study, the flow through a simple low-cost flume constructed using two semi-cylinder contractions on either side of a rectangular channel was experimentally investigated. In practice, these flumes may operate under free- or submerged-flow conditions depending on the downstream flow depth. To reliably estimate the flume discharge, free- and submerged-flow conditions should be accurately distinguished. At present, there is no equation to estimate the submergence threshold. This study investigates the possibilities of using these flumes under submerged-flow conditions. The discharge of the submerged flume may be calculated on the basis of the free-flow discharge equation. Thus, two new free-flow discharge equations were deduced: a general equation by considering the contraction ratio with an average error of 2.25%, and another one by neglecting it with an average error of 4.88%. Compared with the existing discharge equations, the proposed free-flow equations are the best ones. Under submerged-flow conditions, the submergence ratio affects the flow discharge. Using the measurements carried out in this study, the submergence threshold ratio and submerged-flow discharge were formulated and calibrated with the average errors of 2.96% and 3.80%, respectively. The equation to distinguish the free- and submerged-flow conditions was also deduced by equating the submerged- and free-flow discharge equations yielding a novel real solution.     

基于泵送压力的混凝土泵排量计量方法

分析现有混凝土泵排量计量方法的特点,指出现有计量方法在计量精度方面的不足.根据混凝土泵工作原理建立混凝土泵排量数学模型,指出计量混凝土泵排量的关键是实时泵送效率系数.分析影响实时泵送效率系数的因素以及混凝土缸压力与主液压缸压力之间的关系,提出基于泵送压力的计量方法.通过直接测量混凝土泵主油缸压力,分析主油缸压力变化趋势,计算实时泵送效率系数,对混凝土泵实际排量进行计量.试验表明,所提方法具有较高计量精度.     

聚丙烯装置在无规共聚生产状态下的长周期运行

无规共聚PP具有良好的透明性和热封性能,其消费和生产量逐年增加。研究了采用液相本体Spheripol技术生产无规共聚物时,聚丙烯装置遇到的环管带连接堵塞、高压闪蒸罐D2301架桥、汽蒸器D2501下料阀堵塞等问题,通过原因分析,采取了如下措施:在无规物转产均聚物时控制Donor的加入量,在生产无规物时控制Atmer163的加入量,改造降温针形阀,保障了装置的长期稳定运行。