A New Indicator for Unsteady Flow Analysis in Pressurized Irrigation Systems

Pressurized irrigation systems operating on-demand offer large flexibility to farmers for managing their irrigation practices. Within these systems, the fast moving water and the sudden closing of hydrants generates unsteady flow and may create a significant pressure variation in the pipes causing noise, vibration and, sometimes, also pipes’ collapse. The present study describes a simulation tool that was developed for the analysis of unsteady flow effects. A large number of configurations of hydrants simultaneously open has been used to reflect farmers’ behaviour. A new indicator, called Relative Pressure Variation (RPV), was proposed to evaluate the pressure variation occurring into the system in respect to the steady-state pressure. This is very relevant and can be used to identify pipes with potential risk of failure. In addition, an analysis with different gate-valves’ closing time was carried out. It demonstrated that closing time shorter than Tc?=?3 s may create dangerous pressures for the pipes.     

A Multiscale Approach to Leak Detection and Localization in Water Pipeline Network

Leak detection and localization in water pipeline networks is of paramount importance to industry, especially in regions where water is scarce. In this paper, we present a novel multi-modal and multi-scale approach for leak detection and localization in water pipeline networks, in which pressure measurements at various points on the network are used to localize the pipe segment in which the leak is occurring, and then the vibration sensors are used to localize the leak within this segment. In some situations where the complete pipeline model is not available, pressure data alone may not be effective in localizing the leak. However, in such a situation, by supplementing pressure data with vibration data, the leak can be localized, as these additional data are easier to acquire at arbitrary points, since vibration sensors are non-invasive. In order to validate the effectiveness of the approach that needs both pressure and vibration data, we simulate the pipeline model using EPANET that includes models for flow and pressure at various points on the pipeline, then integrate the vibration model with it in MATLAB, since EPNAET does not include models for vibration measurements. A case study of a pipeline network is considered, and the proposed scheme is used to detect and localize the leak. Extensive simulation results show the effectiveness of the proposed scheme in providing accurate leak detection and localization.     

Development of Multiple Leakage Detection Method for a Reservoir Pipeline Valve System

The detection of multiple leakages in pipeline systems has been one of the challenging issues for the control of water loss in water distribution systems. Inverse transient analysis can be a useful principle for predicting leakage through the calibration of location and leakage quantity, based on the pressure reflection that originates from an abnormal boundary condition. In this study, an innovative leakage detection method is proposed to address unknown conditions on multiple leakage dimensions through introduction of revised leakage expressions based on a frequency domain approximation. A multiple leakage function was modified for an efficient representation of multiple abnormalities at a reservoir pipeline valve system. An iterative metaheuristic scheme (IMS) was designed to handle an optimization scheme for multiple leakages using a pressure response for a discharge impulse introduced through value manipulation. In order to address unsteady friction in hydraulic transients combined with multiple leakages, both one-dimensional and two-dimensional models were used to derive leakage expressions for turbulent and laminar flow conditions. An isolated multiple leakage function (IMLF) was proposed to exclusively encapsulate the impact of leakages and unsteady fiction. Considering uncertainties in the hydraulic transient propagation, data noise, and multiple local optima issues in large parameter calibrations, three advanced schemes were modularized to improve detectability of IMS. Several hypothetical examples were presented to show the potential of IMS, validity of three advanced schemes, and robustness in multiple leakage prediction compared to existing approaches.     

EXPERIMENTAL INVESTIGATION OF CHARACTERISTIC FREQUENCY IN UNSTEADY HYDRAULIC BEHAVIOUR OF A LARGE HYDRAULIC TURBINE

The features of unsteady flow such as pressure variation and fluctuation in a large hydraulic turbine usually lead to the instability of operation.This article reports the recent in site investigation concerning the characteristic frequencies in pressure fluctuation,shaft torsional oscillation and structural vibration of a prototype 700 MW Francis turbine unit.The investigation was carried out for a wide load range of 200 MW-700 MW in the condition of water head 57 m-90 m.An extensive analysis of both time-history and frequency data of these unsteady hydraulic behaviours was conducted.It was observed that the pressure fluctuation in a draft tube is stronger than that in upstream flow passage.The low frequency with about one third of rotation frequency is dominative for the pressure fluctuation in part load range.Also the unsteady features of vibration of head cover and torsional oscillation of shaft exhibited the similar features.Numerical analysis showed that the vibration and oscillation are caused by vortex rope in the draft tube.In addition,a strong vibration with special characteristic frequency was observed for the head cover in middle load range.The pressure fluctuation in the draft tube with the same frequency was also recorded.Because this special vibration has appeared in the designed normal running condition,it should be avoided by carefully allocating power load in the future operation.     

有气阀的长距离输水管道流动特性分析与应用

长距离输水管道为了补(排)气需要安装气阀，气阀工作时在阀附近的管道内会形成空穴，并且以气阀为中心，上下游管系、空穴和气阀组成一个局部的小系统，形成管系水流特性、空穴参数和过阀气流特性的连续同步变化，并使管内出现振荡流动。本文通过计算实例对过阀气流参数按等熵流动过程计算，空穴参数按等温过程计算，上、下游管系内的水流特性则按非定常流动计算，其计算结果基本符合实际情况。由此得到的过阀气流的质量流量，可用于选择气阀的过流面积，而管系内水流的振荡流动特性，可供管道系统设计、气阀布设安装时参考。     

管道泄漏检测的水力瞬变全频域数学模型

输水管道泄漏孔的存在及其位置直接影响着系统压力波形的畸变和衰减特性,通过分析有、无泄漏时任意位置处的压头频域特性可使泄漏检测成为可能.在考虑非恒定摩阻影响的基础上,提出基于水力瞬变全频域数学模型的泄漏检测反问题分析方法.用拉氏频域变换处理边界条件和实测数据,并将遗传算法用于频域反问题模型的求解,在寻优速度上比传统的瞬变时域分析的方法有了较大的改善.算例表明基于水力瞬变全频域数学模型分析的管道泄漏检测是一种有效的新方法.     

Valve Maneuver Prediction in Simple and Complicated Pipeline Systems

The pressure and flow variations in pipeline systems are extremely sensitive to dynamic operations of the valves. Valve control and propagation of pressure waves along pipelines and their interactions with different pipeline elements introduce pressure transients in pipeline systems. The time series of the pressure head at any designated position depends on boundary conditions such as valve maneuver as well as geometrical and material characteristics of the pipeline system. An innovative method is proposed to calibrate the valve trajectory using pressure head records. The impedance method and particle swarm optimization were integrated with decomposition of convolution between the pressure response function and time series of the valve maneuver. To validate the applicability of this study, the developed method was tested in three hypothetical pipeline systems: a simple reservoir pipeline valve, multiple reservoir pipeline valves, and a complicated pipe network. Decomposition of the transfer function in the time domain and its convolution contributed toward improving the efficiency of the developed method. The successful calibrations of valve actions demonstrate the potential of the proposed scheme as an alternative to conventional flow meters for high-resolution flow rate evaluation.

     

超长倒虹吸出口明满流仿真闸门动态边界设置方法

鄂北调水工程中的孟楼-七方倒虹吸长达72km,其闸门调控下的出口边界设置对倒虹吸管内水力响应过程有显著影响。超长倒虹吸出口闸门处于有压段与明渠段的交界处,属于长有压管道闸孔淹没出流,具有高度耦合、非线性化的特点。常用的有压隧洞泄流公式未考虑倒虹吸内的非恒定流运动,不适于作为长倒虹吸出口边界,Henry公式能够合理反映闸门调控下的水力响应规律,但难以反映水击震荡特性。在此基础上,提出一种将出口闸门涵管化的边界处理方法,仿真结果揭示出在快速关闸时倒虹吸管中伴随有显著水击振荡,下游段事故工况中最大水击压强达25.1m(初始压强为8.8m),最大水击振幅为16m,压强变化特性与类似试验结果相符。提出的方法可为鄂北调水工程的事故工况调度提供技术支撑,也可为类似明满流动态边界仿真建模提供参考。     

Impedance Method for Abnormality Detection of a Branched Pipeline System

In this paper, an integrated detection scheme is developed to simultaneously address a leakage, a partial blockage and unknown branched pipeline elements. Expressions for the pressure head and discharge for a branched pipeline system having both a leakage and a blockage are derived in frequency domain. Boundary conditions for a reservoir and a branched dead-end allow the development of impedance formulations. The condition for a pipeline junction can be addressed using either a common condition for the pressure head combined with a continuity condition of discharge or a connectivity condition for impedance. In order to consider the unsteady friction’s impact, the impedance development process studied both the impact resulting from velocity profiles with two-dimensional distributions and the impact resulting from local and convective accelerations. Impedance expressions are derived for two distinct branched pipeline systems at different abnormality conditions. Based on drived formulations describing these systems, response functions were derived in the frequency domain and their corresponding time domain representations were integrated into a meta-heuristic calibration scheme for inverse transient analysis. Using an objective function for minimization of root-mean-square-errors between the observed and computed pressures, the calibration based one impulse response can simultaneously predict locations and magnitudes of abnormalities as well as parameters for a branched pipeline. The strength of the impedance-based approach for inverse transient analysis arises mainly from its feasibility to address different conservation conditions for pressure and discharge and for combining these conditions into a unified impedance connectivity condition.     

RTU系统在城市引水工程中的应用与施工技术

城市引水工程中的长途输水管线,全程各个关键点的压力监测,直接影响输水系统的安全运行与调控。利用RTU系统完成长输管线压力监测点的数据采集,并通过GPRS与供水调度监控中心组成远程数据采集和监督控制（SCADA）系统,达到引水工程全线的压力监测。以哈尔滨市磨盘山水库引水工程为例,介绍了RTU系统的构成、系统的功能描述、RTU系统工程在安装过程中的关键工艺控制。以期对RTU系统应用的工程技术和维护人员,提供一些实践经验和教训。     

长引水系统电站过渡过程数字仿真

水力过渡过程计算是水电站和水力机组设计不可或缺的一项工作,也是保证电站尤其是长引水系统电站安全稳定运行的前提。为了确保电站甩负荷过渡过程的安全,以有压管道非恒定流微分方程组为基础,采用特征线法,对具有上游调压室,一洞三机布置的复杂引水管路系统建立了数学模型,并进行了机组甩负荷过渡过程仿真计算。最终,确定了合理的导叶关闭规律,给出了相关参数随时间变化的历程线,并计算了调压井的最高、最低涌浪,为该电站的设计及安全稳定运行提供了技术依据,同时对类似工程也具有一定的参考价值。     

液体管道高频水力瞬变过程的数值模拟

目前在液体管道高频水力瞬变分析中,人们通常采用经典的拟稳态摩阻模型进行分析.但这种方法针对管壁切应力具有拟稳态特性的缓慢瞬变的分析是可行的,而对高频瞬变流动过程而言却不能准确预测水击压力波具体的衰减过程以及出现的波形畸变现象.介绍了一种新的考虑瞬时加速度对高频水力瞬变过程影响的非恒定摩阻模型,并结合特征线法给出了其数值解法,最后通过实例验证了该模型能比经典的拟恒定摩阻模型更为准确地模拟液体管道中高频瞬变流压力波的衰减和波形畸变.该模型对计算机的要求和计算耗时与经典的拟稳态摩阻模型相差不大,是一种具有良好工程应用潜力的液体管道高频瞬变分析数学模型.     

李家峡水电站机组开停机过程非平稳振动信号的小波分析

基于李家峡水电站双排机组振动的现场试验研究，并且针对传统频谱分析方法傅立叶变换（FFT）对于非平稳信号已力不从心这一缺陷，利用小波分析方法在时域和频域上同时具有良好的局部化性质，通过对开停机这一典型非平稳过程信号进行小波及小波包分析，将其分解到不同频带内，获取微弱信息和提取优势频率，并对其作振源分析，得出开停机初始时刻因水流不稳均出现强烈的振动现象，且低频段信号能量最大，开停机过程水流脉动压力和尾水涡带摆动是引起定子基础振动的主要原因。同时也证明了小波是处理非平稳信号的最有力的工具。     

抽水蓄能电站水力 机械系统自激振动特性研究

针对部分抽水蓄能电站运行过程中出现的水力-机械振动以及运行不稳定现象，从水力阻抗的角度研究可逆式机组可能产生自激振动的判别条件以及相应的不稳定区域。应用非线性振动理论，分析抽水蓄能电站产生自激振动时的幅频特性。结合具体算例，考虑可逆式机组在不稳定区域(“S”形特性区)运行时，进行水力-机械系统的自由振动分析，在全频域范围内分析系统的振动特性，得出相应衰减因子为正的振动模式，同时结合特征线法在时域内进行自激振动分析，给出相应的振动曲线。研究结果表明抽水蓄能电站自激振动由多个衰减因子为正的振动模式叠加而成，其最大幅值与理论分析一致。     

抽水蓄能电站水力-机械系统自激振动特性研究

针对部分抽水蓄能电站运行过程中出现的水力-机械振动以及运行不稳定现象,从水力阻抗的角度研究可逆式机组可能产生自激振动的判别条件以及相应的不稳定区域。应用非线性振动理论,分析抽水蓄能电站产生自激振动时的幅频特性。结合具体算例,考虑可逆式机组在不稳定区域("S"形特性区)运行时,进行水力-机械系统的自由振动分析,在全频域范围内分析系统的振动特性,得出相应衰减因子为正的振动模式,同时结合特征线法在时域内进行自激振动分析,给出相应的振动曲线。研究结果表明抽水蓄能电站自激振动由多个衰减因子为正的振动模式叠加而成,其最大幅值与理论分析一致。     

Hydraulic characteristics of a siphon-shaped overflow tower in a long water conveyance system: CFD simulation and analysis

The siphon-shaped overflow tower is a new type of pressure-suppressing structure used in long water conveyance systems,and it plays a crucial role in guaranteeing the system’s stability and safety during hydraulic transient processes.The flow in the tower is characteristic of weir flow in a closed duct,and is thus a complex air-water two-phase flow.Intensive studies of the flow patterns,the pressure pulsations,and the discharge capacity are necessary for better understanding of the flow processes and for the purpose of design.In this paper,we simulate the flow in a siphon-shaped overflow tower under both steady and unsteady flow conditions.Through a steady-flow field simulation,the relationship between the overflow discharge and the pressure in the connected pipeline is analyzed and an empirical formula for evaluating the discharge capacity is provided.Through a transient-flow field simulation,the negative-pressure distributions on the weir crest,the pressure pulsations on the crest and in the falling pond,and the transformation of the air-water two-phase flow in the downstream outlet pipe are analyzed.Moreover,the major influencing factors of the flow patterns,especially,the sectional area of the air vents,are clarified.It is indicated that the siphon-shaped overflow tower can regulate the pressure surge during hydraulic transients and guarantee the safety and stability of the pipeline system,if the shape and the vents are properly designed.     

供水管线渗漏水力分析

基于供水管网水力计算理论，建立了以渗漏强度对管线压力的主要影响因素的渗漏状态下管道水力计算模型。应用该模型，可以得到正常与渗漏两种状态下的压力差值的数学表达式与其变化规律，据此可根据压力变化判据渗漏和进行定位。通过模拟计算，介绍了压力变化作为渗漏发生有效判据和初步定位的方法。     

大型水轮机不稳定流体与结构耦合特性研究Ⅰ：耦合模型及压力场计算

为了分析压力脉动及其诱发的结构振动等不稳定问题,对大型水轮机在不稳定条件下的流固耦合算法进行了研究。建立了非定常条件下耦合问题的控制方程及其定解条件,探讨了耦合界面模型在耦合分析过程中的作用,提出了一种适合于大型水轮机不稳定压力场与结构场耦合分析的界面模型,分析了以求解转轮区压力脉动为主要目标的非定常湍流计算模式。结合某大型电站,建立了原型水轮机非定常耦合计算模型,详细给出了转轮区不稳定压力场的分布特征,为下一步开展结构动态响应分析奠定了基础。     

An integral calculation approach for numerical simulation of cavitating flow around a marine propeller behind the ship hull

In this paper, the unsteady cavitating turbulent flow around a marine propeller is simulated based on the unsteady Reynolds averaged Navier-Stokes(URANS) with emphasis on the hull-propeller interaction by an integral calculation approach, which means the propeller and hull are treated as a whole when the cavitating flow is calculated. The whole calculational domain is split to an inner rotating domain containing a propeller and an outer domain containing a hull. And the two split sections are connected together in ANSYS CFX by using the GGI interfaces and the transient rotor stator frame change/mixing model. The alternate rotation model is employed for the advection term in the momentum equations in order to reduce the numerical error. Comparison of predictions with measurements shows that the propeller thrust coefficient can be predicted satisfactorily. The unsteady cavitating flow around the propeller behind the ship hull wake shows quasi-periodic features including cavity inception, growth and shrinking. These features are effectively reproduced in the simulations which compare well to available experimental data. In addition, significant pressure fluctuations on the ship hull surface induced by the unsteady propeller cavitation are compared with experimental data at monitoring points on the hull surface. The predicted amplitudes of the first components corresponding to the first blade passing frequencies match well with the experimental data. The maximum error between the predictions and the experimental data for the pressure pulsations is around 8%, which is acceptable in most engineering applications.     

轴流式水轮机模型飞逸过程三维湍流数值模拟

通过作者建立的非稳态过程三维湍流数值模拟方法,模拟了轴流式水轮机模型飞逸过程,并进行了其三维数值湍流计算,获得了机组到达最大转速时所需时间、最大飞逸转速值、飞逸过程内特性流场演变规律以及转速、流量、力矩与测点静压随时间变化的曲线。计算结果表明,所得最大飞逸转速与试验值非常接近,误差在1.5%以内;所得力矩及流量等外特性参数变化过程均符合高比转速水轮机理论特性;当转速增大到某一数值之后,尾水管水力稳定性急剧恶化是引起机组振动的主因。