Pseudotransient Continuation Method in Extended Period Simulation of Water Distribution Systems

This paper presents and discusses a new static solver that implements the pseudotransient continuation method for the quasi-steady state analysis, or extended-period simulation of water distribution systems. The implementation is based on the concept of virtual tanks and has a clear physical meaning. The steady state solver described in this paper can analyze a pipe network under pressure deficient conditions and is free from some convergence problems that occur in the Newton-Raphson method-based solvers when analyzing a pipe network with control devices. The numerical examples considered in the paper demonstrate the convergence of the proposed method in cases where existing static solvers (e.g., that of the EPANET 2 hydraulic simulator) fail.     

Impulse Response Method for Pipeline Systems Equipped with Water Hammer Protection Devices

Surge protection devices, such as surge tanks and air chambers, have been modeled with the impulse response method for transient analysis of water distribution systems. The lumped inertia model and continuity equation are used to represent nonpipe hydraulic elements. Results of pressure or discharge variations obtained by using the impulse response method and the method of characteristics are in good agreement. The impulse response method provides total pressure and discharge along any pipeline segment by direct integration of the ratio of complex head or complex discharge to a complex downstream discharge, respectively. A modification is proposed so that transition between turbulent and laminar flows can be considered. The representation of hydraulic devices has been incorporated into the impedance matrix method, which was developed for heterogeneous and multilooped pipe network systems. The potential advantages of the proposed method over other conventional approaches were investigated by applying the proposed method to hypothetical pipe network systems.     

Improved Control of Pressure Reducing Valves in Water Distribution Networks

The behavior of transients in water pipe networks is well understood but the influence of modulating control valves on this behavior is less well known. Experimental work on networks supplied through pressure reducing valves (PRVs) has demonstrated that, in certain conditions, undesirable phenomena such as sustained or slowly decaying oscillation and large pressure overshoot can occur. This paper presents results from modeling studies to investigate interaction between PRVs and water network transients. Transient pipe network models incorporating random demand are combined with a behavioral PRV model to demonstrate how the response of the system to changes in demand can produce large or persistent pressure variations, similar to those seen in practical experiments. A proportional-integral-derivative (PID) control mechanism, to replace the existing PRV hydraulic controller, is proposed and this alternative controller is shown to significantly improve the network response. PID controllers are commonly used in industrial settings and the methods described are easy to implement in practice.     

Heat Pipe Augmented Passive Solar System for Heating of Buildings

A passive solar heating system was built using heat pipes bonded to the absorbing surface of a solar collector mounted on the south wall of a building. The heat pipes provided one-way heat transfer from the absorber through the insulated wall of the building to water tanks placed inside the space to be heated. The space was then heated by means of natural convection from the surfaces of the tank. The evaporator and condenser ends of the heat pipe were designed to be connected by means of a flexible hose so that the system could be retrofit to an existing building. Simulations were carried out to match the experimental and simulated results. The conductance values obtained as a result of matching showed good agreement with theoretically calculated values. Potential performance improvements were identified, including increased liquid fill fraction in the heat pipes and increasing the heat transfer surface area of the water tanks at the condenser end of the pipe.     

Optimal Distribution and Control of Storage Tank to Mitigate the Impact of New Developments on Receiving Water Quality

Storage tanks are commonly installed in a combined sewer system to control the discharge of combined sewer overflows that have been identified as a leading source for receiving water pollution. The traditional approach to determine the distribution of storage tank volume in the sewer system is confined to the use of objectives within the system itself due to the limits of separate modeling of urban wastewater systems, consisting of the sewer system, wastewater-treatment plant, and receiving water. The aim of this study is to investigate the optimal distribution and control of storage tanks with an objective to mitigate the impact of new residential development on receiving water quality from an integrated modeling perspective. An integrated urban wastewater model has been used to test three optimization scenarios: optimal flow rate control, storage distribution, and a combination of these two. In addition to the cost of storage tank construction, two receiving water quality indicators, dissolved oxygen and ammonium concentration, are used as optimization objectives. Results show the benefits of direct evaluation of receiving water quality impact in the context of storage distribution optimization. Results indicate that storage allocation should be considered in conjunction with optimal flow rate control to achieve the maximum effectiveness in water pollution mitigation.     

Pilot-Scale Verification and Analysis of Iron Release Flux Model

An original model by Mutoti in 2003 was developed mathematically, and empirically, to predict the increase in total iron concentration in distribution systems. This model, referred to as a flux model, relates the increase in iron concentration in a reach of unlined or galvanized iron pipe to the surface area of the pipe in contact with the water. A flux term, defined with a dimension of mass per area per time was used. The effects of water chemistry, pipe material and hydraulic conditions were incorporated into the flux term. This paper describes the verification of the flux model using independent pilot data obtained with variable water quality under worst case, laminar flow conditions. The original model accurately predicted iron release for this independent verification data, with an overall R2 of 0.80. For laminar flow conditions, the increase in iron concentration is proportional to the flux and the hydraulic residence time, and is inversely proportional to the pipe diameter.     

Reduction of Mixing in Jet-Fed Water Storage Tanks

Contrary to usual mains-water practice, mixing in water storage tanks used in rainwater harvesting systems is undesirable because pathogen die-off can occur in the unmixed water prior to its extraction for use. The principal cause of mixing in these tanks is the momentum of the inflow during a rainfall event. We investigate the effect of inflow-jet configuration on the proportion of stored water in a tank which mixes with the slightly cooler inflow of rooftop water. Scale experiments are conducted which show that the nondimensional height of the mixing front above the jet inlet is proportional to the inflow-jet densimetric Froude number for both single and multijet arrangements of various geometries. For each arrangement a coefficient of mixing is found. The results are then used to assess the level of mixing in full-scale rooftop rainwater harvesting storage tanks and determine whether residence time in such tanks is a viable strategy for pathogen reduction. For such applications, a radial manifold of jets outwardly directed from the tank center is found to be the most promising.     

Efficient Quasi-Two-Dimensional Model for Water Hammer Problems

Quasi-two-dimensional models for turbulent flows in water hammer are necessary for advancing the understanding of flow behavior in pipe transient; conducting detailed investigation of the fate of transient-induced contamination; and validating one-dimensional water hammer models. An existing quasi-two dimensional numerical model for turbulent water hammer flows has the attributes of being robust, consistent with the physics of wave motion and turbulent diffusion, and free from the inconsistency associated with the enforcement of the no slip condition while neglecting the radial velocity at boundary elements, such as valves and reservoirs. However, this scheme is computationally intensive making it unsuitable for practical pipe systems or for conducting numerical experiments. This paper addresses the efficiency and stability of this existing scheme. In particular, algebraic manipulations show that the original scheme can be decoupled into two tridiagonal systems, one for piezometric head and radial flux and another for axial velocity. This decoupling is the reason for the high efficiency of the modified scheme. The original and proposed schemes are applied to a pipe–reservoir–valve system. It is found that, for the same spatial and temporal discretization, both schemes are of equal accuracy. However, significant saving in computer execution time is achieved by using the modified scheme. Application of the modified scheme to pipes of realistic dimensions and wavespeeds (length 35.2 km, diameter 200 mm, and wave speed 1000 m/s) takes only a few minutes to execute. This small execution time requirement makes the current quasi-two-dimensional model suitable for application to practical water hammer problems. The stability domain of the proposed scheme is established using the Von Neumann method.     

长距离输水工程瞬态水力计算及处理措施设计

运用Hammer软件对长距离输水工程瞬态进行动态模拟,清晰地呈现了瞬态发生时,随着压力波的推移,管道系统因为管道负压而引起弥合水锤的过程.针对模拟情况,采取在输水管道系统的合理位置增设三功能排气阀、抗水锤泄压阀,在泵站出口设置抗水锤气压罐等联合措施,有效地消除瞬态条件下在管道系统内产生的水锤,保证输水管道系统瞬态的安全...     

正确解决“管网叠压”供水技术推广难题的途径

“管网叠压”供水技术目前正在大面积推广,但绝大多数管网叠压供水设备并没有发挥出应有的作用。原因是供水设备的运行方式不节能、不科学。实践证明：“管网叠压恒压水泵＋屋顶水箱”全自动供水设备是管网叠压供水技术推广的正确途径。     

Mixing in Water Storage Tanks. I: No Buoyancy Effects

The results of extensive experiments on jet-induced mixing in water storage tanks are reported in two papers. The experiments were conducted on three styles of storage tanks using a newly developed three-dimensional laser-induced fluorescence (3DLIF) system that can measure the whole field of tracer concentrations in the tanks and its temporal evolution through the mixing process. Various inlet geometries were tested for each tank style. In this paper, the results of experiments with no buoyancy effects are given. The 3DLIF technique enabled complex flow patterns to be observed such as a donut-shaped dead zone that inhibited mixing in ground-level cylindrical tanks. Values of dimensionless mixing times are presented that enable comparisons of the mixing efficiency of different inlet configurations and allow prediction of mixing times in prototype tanks. For cylindrical tanks, the dimensionless mixing time increases with increasing depth-to-diameter ratio. Vertical nozzles at the bottom mixed most efficiently. If a single vertical nozzle is used, placing it near a sidewall is preferred. Mixing becomes somewhat more rapid as the number of nozzles increase. Mixing times for rectangular tanks are generally similar to cylindrical tanks. The use of a tube intended to enhance mixing actually inhibited mixing in standpipe tanks.     

Forecasting the Remaining Useful Life of Cast Iron Water Mains

Effective asset management strategy of civil infrastructure systems requires integration of technical and financial plans. This is particularly true in managing water mains, which requires knowledge of their current condition and their forecasted remaining useful life. This paper presents a model designed to forecast the remaining useful life of cast iron water mains. The model is easy to use and its generated results are utilized in determining condition rating of the water mains being considered. The model considers factors related to pipe properties, its operating conditions, and the external environment that surrounds the pipe. In addition, it overcomes limitations associated with existing models. Three different data-driven techniques are considered in the model development; each is used to study the relationship between remaining useful life and a set of deterioration factors, and to forecast remaining useful life of cast iron water mains. These techniques are multiple regression and two types of artificial neural networks: multilayer perceptron; and general regression neural network. The data used in model development were acquired from 16 municipalities in Canada and the United States. The results produced by the developed models correlate well with the actual conditions.     

Optimal Design of Level 1 Redundant Water Distribution Networks Considering Nodal Storage

A water distribution network (WDN) is designed to meet time-varying demands with sufficient pressure, taking into consideration an appropriate demand during peak hours. Therefore, a network has inherent redundancy in the sense that under abnormal conditions such as those arising due to pipe breaks or pump failures, deficiency in supply during peak hours can be met through additional supply during off-peak periods. However, this necessitates a storage facility at the consumer end of the network, which is normally available in the form of a sump or an overhead tank in developing countries. Such a storage enables the consumer to store water during the off-peak period and then use it during the peak period. Reliability of a WDN is assessed herein considering nodal storage, and an iterative method is proposed for the optimal design of Level 1 redundant WDNs, i.e., networks that can sustain a single pipe failure without affecting consumer services either in part or in full. The method is illustrated through an example and the designs of a network with and without storage are compared. Provision of a nodal storage is found to reduce the total cost of the network.     

Solute Mixing Models for Water-Distribution Pipe Networks

The spreading of solutes or contaminants through water-distribution pipe networks is controlled largely by mixing at pipe junctions where varying flow rates and concentrations can enter the junction. Alternative models of solute mixing within these pipe junctions are presented in this paper. Simple complete-mixing models are discussed along with rigorous computational-fluid-dynamics models based on turbulent Navier–Stokes equations. In addition, a new model that describes the bulk-mixing behavior resulting from different flow rates entering and leaving the junction is developed in this paper. Comparisons with experimental data have confirmed that this bulk-mixing model provides a lower bound to the amount of mixing that can occur within a pipe junction, while the complete-mixing model yields an upper bound. In addition, a simple scaling parameter is used to estimate the actual (intermediate) mixing behavior based on the bounding predictions of the complete-mixing and bulk-mixing models. These simple analytical models can be readily implemented into network-scale models to develop predictions and bounding scenarios of solute transport and water quality in water-distribution systems.     

Ground Displacements from a Pipe-Bursting Experiment in Well-Graded Sand and Gravel

Pipe bursting is a construction technique that involves the replacement of an existing buried pipe with potentially much less surface disturbance than traditional cut and cover construction. However, excessive ground movements associated with pipe-bursting operations may lead to damage to surrounding infrastructure. A static pipe-bursting experiment was performed in sand and gravel within an 8-m-long, 8-m-wide, and 3-m-deep test pit to quantify the ground displacements from pipe bursting. An existing unreinforced concrete pipe buried 1.385 m below the ground surface was replaced with a high-density polyethylene pipe. Pulling force and the three-dimensional nature of surface displacements associated with pipe bursting are examined. The 4-m wide surface response had a peak vertical displacement of 6 mm. In addition, transverse displacements of 1.2 mm resulted in the formation of a tension crack in the ground above the concrete pipe. This experiment offers data that improves the understanding of the mechanisms of ground disturbance, and provides unique experimental data for calibration of numerical models.     

聚丙烯酸洗槽技术在冷轧生产的应用及展望

酸洗槽是去除热轧板表面氧化铁皮的主体设备,传统酸洗槽设计多选用碳钢衬胶再衬耐酸砖结构,制造工序复杂,维护困难。近年来,聚丙烯(PP)材质以其优越的机械加工性能和耐化学品性能得到广泛应用。对比PP酸洗槽和传统钢衬胶再衬砖结构,PP酸洗槽质量轻,便于运输、安装和质量控制,在越来越多的新旧生产线上取代传统的钢结构形式。分析PP酸洗槽设计方面纵向热膨胀以及回酸口的焊接问题,给出了解决的方案,并展望了PP酸洗槽的应用前景。     

Effect of Tank Size and Geometry on the Flow Induced by Circular Bubble Plumes and Water Jets

Ambient flow field and circulation patterns induced by circular bubble plumes and water jets in tanks of different sizes were studied in rectangular and square water tanks. A nonstationary nature of the flow was observed in all experiments and its dominant oscillation frequency was found to directly relate to the tank size. The flow circulation patterns were similar for bubble plumes and water jets, but changed significantly with tank size and geometry. Strong three-dimensional effects were observed in a rectangular tank, resulting in flow entraining in the longer plane and flow detraining in the shorter plane, especially for the bubble plume tests. A relationship was developed to relate the tank size to the patterns of circulation cells. Nearly isotropic turbulent flow conditions were obtained in all experiments, but the effect of tank size and geometry on the magnitude of the turbulent stresses was more pronounced in the bubble plume tests.     

Models Quantify the Total Maximum Daily Load Process

Mathematical models have been used for many years to assist in the management of water quality. The total maximum daily load (TMDL) process is no exception; models represent the means by which the assimilative capacity of a water body can be quantified and a waste load allocation can be determined such that the assimilative capacity is not exceeded. Unfortunately, in many TMDLs, the use of models has not always adhered to the best modeling practices that have been developed over the past half-century. This paper presents what are felt to be the most important principles of good modeling practice relative to all of the steps in developing and applying a model for computing a TMDL. These steps include: Problem definition and setting management objectives; data synthesis for use in modeling; model selection; model calibration and, if possible confirmation; model application; iterative modeling; and model postaudit. Since mathematical modeling of aquatic systems is not an exact science, it is essential that these steps be fully transparent to all TMDL stakeholders through comprehensive documentation of the entire process, including specification of all inputs and assumptions. The overriding consideration is that data richness and quality govern the level of model complexity that can be applied to a given system. The model should never be more complex than the data allow. Also, in applying a model, one should always attempt to quantify the uncertainty in predictions. In general, quantifying uncertainty is easier with simple models, which is another reason to begin with a simple framework.     

Optimum Design of a Watershed-Based Tank System for the Semiarid and Subhumid Tropics

Small reservoirs known as tanks are constructed in the watersheds of arid, semiarid, and subhumid regions of India to provide supplementary or protective irrigation to crops during dry spells of the monsoon season or full irrigation during the postmonsoon season. The stored water in tanks or recharged groundwater is used for this irrigation. Several models have previously been developed to design the capacity of individual tanks. However, for optimum utilization of water generated in a watershed to meet the demands for irrigation and for downstream release, it is necessary to design the tanks together in terms of their number, locations, and capacities. A comprehensive methodology for this is presented using stream points, i.e., possible tank locations on the main stream(s) in the watershed. Tank strategies (combinations of numbers of tanks, their locations at stream points, and tank types) are then generated for the identified stream points. Subsequently, fields in the watershed are assigned to the catchment and the command of different tanks of a specified tank strategy. Simulation of field, tank, and groundwater balance is then carried out on a daily basis, from which optimum tank dimensions are obtained for a specified tank strategy. The optimum tank strategy and corresponding optimum tank dimensions are obtained by investigating all the possible tank strategies.