水电站进水口渐变段局部水头损失研究

为研究水电站进水口渐变段局部水头损失,分别针对渐变段长度、隧洞长度和圆形隧洞直径三个影响因素,采用CFD方法模拟了15种进水口渐变段,进行数值分析。在此基础上,通过量纲分析研究了水电站进水口渐变段水头损失的敏感性。结果表明:水电站进水口渐变段局部水头损失与渐变段长度、隧洞长度和圆形隧洞直径有关;渐变段长度、隧洞长度对局部水头损失影响较小,而隧洞直径对局部水头损失影响较大。研究结果可为水电站进水口渐变段设计计算提供参考。     

多岔管局部水头损失系数的确定

为了确定多岔管道局部水头损失系数ζ,采用Fluent软件研究了五岔管局部的流速场分布,进而建立h_j~v~2/2g线性关系,从而得到各岔管局部水头损失系数ζ。计算成果与物理模型试验吻合良好,表明该数值模拟方法可用于其他异形体型局部水头损失系数ζ的确定。     

管路突然扩大时局部水头损失的数值模拟

选取了Spalart-Allmaras湍流模型,对Re＜5500时管路中突然扩大的局部水头损失进行了数值模拟.计算结果表明:模拟得到的测压管水头与试验值吻合较好,用断面平均速度计算速度水头时,若取动能修正系数为1.0,则会使局部水头损失的计算值较实际值偏小,速度水头计算方法的影响远大于突然扩大管路的沿程损失对局部水头损失系数的影响.     

阻抗式调压室水头损失系数研究

根据江苏省宜兴抽水蓄能电站尾水调压室局部模型试验结果，研究具有连接管的阻抗式调压室的水力特性，并用查表计算和经验公式计算进行验证，主要研究了连接管中水流方向、连接管道直径以及流量比对调压室水头损失系数的影响．研究表明，模型试验存在一定的误差，在含调压室系统的水力过渡过程计算中，需结合模型试验结果和数值计算结果，确定阻抗式调压室水头损失系数。     

圆断面90°弯管局部水头损失的数值模拟

利用fluent软件,选取标准k-ε湍流模型,对90°圆断面弯管在雷诺数为60000时的局部损失进行了数值模拟。结果表明:标准k-ε湍流模型能较好地预测弯管内由于离心力造成的二次流,弯管内流场及压强分布与试验值吻合较好,计算得到的局部损失系数与试验值基本一致,从而验证了数值模拟方法对弯管局部损失计算的有效性。     

铝塑复合(PAP)管局部水头损失的试验研究

通过对铝塑复合 (PAP)管及配件的试验研究 ,对建筑给水不同供水方式局部与沿程水头损失的计算比较 ,提出了PAP管在建筑给水系统中局部水头损失按沿程水头损失计算的百分数     

矩形明渠消力池水跃的水头损失研究

为了研究沿程水头损失与局部水头损失的变化规律,根据沿程水头损失的基本定义,推求矩形明渠消力池水跃区沿程水头损失与床面阻力系数、水跃共轭水深比、跃前断面宽高比及跃前断面水深的理论关系,提出了矩形明渠水跃区沿程水头损失及其系数和局部水头损失系数的理论公式,给出了沿程水头损失系数、局部水头损失系数和总水头损失系数的简单拟合公...     

闸孔出流局部水头损失系数研究

为了填补现有水力计算手册中关于确定闸孔出流局部水头损失系数的空白,在当前闸孔出流水力计算理论与实践的基础上,根据能量方程导出了平板闸门闸孔出流局部水头损失系数ζ的定量计算公式.即ζ=0.610 3(e/H)3-0.290 8(e/H)2+0.117 5e/H+0.040 6,ζ随闸孔相对开度e/H的增大而增大,其变化范围为0.04～0.16.     

A systematic approach for estimating water losses in irrigation canals

In order to determine water losses in irrigation canals, a systematic approach was developed, consisting of two main components: a seepage simulation model and a hydraulic simulation model. The SEEP/W module of the Geo-Studio software was used to simulate the seepage rate, and the Hydrologic Engineering Center-River Analysis System (HEC-RAS) hydrodynamic model was used for hydraulic simulation. Different operation scenarios were designed to investigate all possible situations in daily operation of water distribution and delivery systems. The seepage simulation results show that the seepage losses were higher at the bottom and corners of the canal, because the hydraulic gradient was affected by the hydraulic load. The hydraulic simulation results show that due to physical and management infrastructure (using non-automated and operator-based regulation structures), operational losses accounted for a significant volume of losses compared to seepage losses. In most operation scenarios, the maximum seepage loss was 10%, and the remaining 90% was related to operational losses. It is concluded that any factor (decrease or increase of inflow to the canal) that causes an increase or decrease of operational losses is ultimately a determining factor in reducing or increasing total losses. Therefore, management approaches should be adopted to improve performance of the system and reduce losses, especially operational losses, by improving the operation methods of water level regulation and off-take structures.     

Flow regime and head loss in a drip emitter equipped with a labyrinth channel

Labyrinth channels are widely adopted in emitter designs to regulate the water flow.The flow regime and the head loss of labyrinth channels have significant impacts on the hydraulic performance of emitters.In this study,the flow behavior of water passing through an emitter channel is observed using the micro particle image velocimetry(PIV),and the head loss during the flow is analyzed for an emitter with a triangular labyrinth channel.The results show that the flow regime is consistent with the classical theory of hydraulics governing straight channels,even when the cross-sectional area is very small(as small as 0.5 mm×0.5 mm).The critical Reynolds number from laminar to turbulent flows in a labyrinth channel is approximately in a range between 43 and 94.The local head loss factor decreases as the Reynolds number increases for labyrinth channels with smaller cross-sectional areas,such as 0.5 mm×0.5 mm and 1.0 mm×1.0 mm.The local head loss factor is not related to the Reynolds number and is only a function of the boundary conditions of the labyrinth channel when the Reynolds number exceeds approximately 1 000(for cross-sectional areas of 1.5 mm×1.5 mm and 2.0 mm×2.0 mm).The ratio of the local head loss to the total head loss total( /)j fh h first increases and then remains nearly constant as the Reynolds number increases in the labyrinth channel.The head loss in the labyrinth channel is almost equal to the local head loss,and total( h_j/h_(ftctal))is approximately 0.95 for cross-sectional areas of greater than 1.0 mm×1.0 mm.These results can be used for optimizing the design of emitter channels.     

倒虹吸有压弯管的局部水头损失系数计算方法比较

有压弯管局部水头损失计算在倒虹吸等过水建筑物设计中至关重要。其中,转弯角和转弯形式是影响局部水头损失系数取值的重要因素。本文通过比较分析典型的有压弯管局部水头损失系数计算公式,结合水工模型试验资料的验证,考察了不同计算公式的性能。对小转弯角(<20°)情形,分析了转弯半径和转弯形式对局部水头损失系数的影响。结果表明,转弯角小于17°时,折弯管的局部水头损失系数不大于圆形缓弯管,在低水头、大流量的输水工程的倒虹吸设计中可以考虑采用折弯管形式。     

An analysis of relay protection requirements for the purpose of estimating its effectiveness

Existing requirements, used to estimate the effectiveness of relay protection, are analyzed. The need to include in these requirements economic indicators of the functioning of relay-protection devices and automation or the reliability of the electric supply, taking into account the results of the functioning of these devices, is validated. This enables the effectiveness of the decisions taken when choosing relay protection and automation devices to be increased.     

Using the W&H integrated uncertainty analysis framework with non-initiated experts.

The W&H (Walker and Harremo?s) integrated uncertainty analysis framework was put forward with the aim of providing a conceptual basis for the systematic treatment of uncertainty in model-based decision support activities such as policy analysis, integrated assessment and risk assessment. It provides a heuristic tool that can be applied in decision support exercises to classify and report the various dimensions of uncertainty. The intention is to stimulate better communication among analysts as well as between them and policymakers and stakeholders. The framework successfully articulates diverse scholarly understandings of 'uncertainty', 'ignorance', and 'quality' in science for policy, Nevertheless, experience with the W&H framework has revealed that many of the concepts put forward are relatively unfamiliar--and perhaps somewhat controversial--to experts practising decision support. Thus, efforts are required to communicate the W&H framework to experts in such a way that their knowledge of uncertainty is elicited adequately, without them being overly intimidated or confused by the novelty of the concepts presented to them. After introducing the W&H conceptual framework, this paper presents the methodology that was used in applying the W&H framework in expert elicitations on uncertainty in the risk assessment of genetically modified crops. Experiences with the use of this methodology are discussed and recommendations for further improvement are given.     

伸缩装置在输煤系统中的经济性分析

根据伸缩装置的结构和功能特点,结合火力发电厂输煤系统的情况,以秦皇岛煤码头和漯河热电厂输煤系统为实例,就伸缩装置在火力发电厂输煤系统中的经济性和适用性进行了分析,得出了伸缩装置更适合在工作位数大于2的大型胶带输送机上应用的论点     

用Matlab实现加筋土结构整体稳定性可靠性分析

结构的整体稳定在结构设计中非常重要,特别是对较高的加筋土墙,该文将重点对加筋土挡墙进行整体稳定性的可靠性分析,通过将加筋体看成一般重力式墙,用圆弧法得到护坡的最危险滑动面及中心点,并建立极限状态方程,运用Matlab中实现蒙特卡罗法的编程。基于加筋土结构整体稳定性的可靠性分析,具有明显的理论意义和很大的实用价值。