Leakage detection and location in water distribution systems using a fuzzy-based methodology

Loss of water due to leakage is a common phenomenon observed practically in all water distribution systems (WDS). However, the leakage volume can be reduced significantly if the occurrence of leakage is detected within minimal time after its occurrence. This paper proposes a novel methodology to detect and diagnose leakage in WDS. In the proposed methodology, a fuzzy-based algorithm has been employed that incorporates various uncertainties into different WDS parameters such as roughness, nodal demands, and water reservoir levels. Monitored pressure in different nodes and flow in different pipes have been used to estimate the degree of membership of leakage and its severity in terms of index of leakage propensity (ILP). Based on the degrees of leakage memberships and the ILPs, the location of the nearest leaky node or leaky pipe has been identified. To demonstrate the effectiveness of the proposed methodology, a small distribution network was investigated which showed very encouraging results. The proposed methodology has a significant potential to help water utility managers to detect and locate leakage in WDS within a minimal time after its occurrence and can help to prioritise leakage management strategies.     

事故状态下供水管网的拓扑分析

当供水管网发生类似于爆管或水质污染等事故时,通过拓扑分析快速找到并关闭相应阀门以孤立事故源进而开展事故抢修是非常必要的。结合事故发生时管网的拓扑结构特点,以图论的理论和方法为基础,提出了一种可用于事故状态下供水管网拓扑分析的方法。该方法首先利用深度优先搜索算法找到距离事故源最近的阀门,然后通过剔除冗余阀门而确定最优关阀方案及关阀后的事故影响区域,最后调整管网水力模型以适应关阀后管网需水量和拓扑结构的变化。该方法不仅可用于供水管网事故时的关阀调度,还可用于供水系统污染控制分析以及供水管网的性能评价。     

Optimal design of water distribution systems

In this paper, the similarities between a water distribution system (WDS) and a structural truss are discussed. Based on this discussion, the problem of determining the optimal design of a WDS is studied by extending some of the methods used to good effect in structural optimization. Two sensitivity analysis methods for node heads, i.e. virtual-discharge method and pseudo-discharge method, are proposed, and the sensitivity formula for pipe flowrates is derived. An algorithm based on the Sequential Linear Programming (SLP) technique is suggested. Finally, two numerical examples are presented.     

Using Evolutionary Optimization Techniques for Scheduling Water Pipe Renewal Considering a Short Planning Horizon

Abstract: The maintenance and management of underground infrastructures is a growing problem for a majority of municipalities. The maintenance costs are increasing while the financial resources of municipalities remain limited. Water distribution system (WDS) managers therefore need tools to assist them in the elaboration of pipe renewal management plans. In this article, results of a newly developed strategy for pipe renewal based on a cost function are presented. The strategy allows the minimization of a cost function while also considering hydraulic criterion. This strategy was tested on a short planning horizon of five years. The pipe number to be replaced and the optimal moment for renewal are identified using three different optimization techniques: IGA (Island Genetic Algorithm), NPGA‐2 (Niched Pareto Genetic Algorithm 2), and NSGA‐II (Non‐dominated Sorting Genetic Algorithm‐II). The proposed approach has five distinctive features: (1) it is coupled with a flexible evolutionary framework that allows the user to select any type of operator for IGA or any kind of multiobjective genetic algorithm; (2) it uses the hydraulic simulator Epanet2.0 which allows steady state or dynamic simulations; (3) it considers a probabilistic break model to evaluate the structural deterioration of pipes; (4) it integrates a Bayesian approach for the estimation of the pipe break model parameters that take into account the influence of inherent uncertainties related to the quality of data during the decision‐making process; and (5) it simulates the variation of the pipe's roughness over the years. The developed strategy/model is explained using an example that allows us to elucidate its most important components. Simulation experiments on a small network (100 pipes) are presented. A comparison of three evolutionary algorithm results is provided. Tests showed that IGA performs well, but for networks of larger sizes, we recommend increasing the number of demes to reach better solutions. Higher quality results were achieved with NSGA‐II than NPGA‐2 on differently sized networks. We recommend the use the NSGA‐II to optimize large WDS. Future developments for this strategy are also discussed.     

实数型编码遗传算法校核管道摩阻系数

通过测试消防栓等手段，产生用于管网参数校核的不同工况，并对管网中管道摩阻系数进行合理分组，构建参数校核的最优化数学模型，利用实数型编码的遗传算法进行求解，结果表明可以较好地修正管道摩阻系数值，提高模型的使用精度。     

用摩阻灵敏度系数法进行管网模型的校正

利用摩阻灵敏度系数法即通过调整对那些需要校正的管段压力或节点流量较敏感的某一管段的摩阻系数,达到对管网水力模型校正目的,使其符合管网的实际工况,并最终服务于管网规划及管道改扩建、检漏、纠漏等实际工作。     

Calibration of denitrifying activity of polyphosphate accumulating organisms in an extended ASM2d model

This paper presents the results of an experimental study for the modelling and calibration of denitrifying activity of polyphosphate accumulating organisms (PAOs) in full-scale WWTPs that incorporate simultaneous nitrogen and phosphorus removal. The convenience of using different yields under aerobic and anoxic conditions for modelling biological phosphorus removal processes with the ASM2d has been demonstrated. Thus, parameter η_PAO in the model is given a physical meaning and represents the fraction of PAOs that are able to follow the DPAO metabolism. Using stoichiometric relationships, which are based on assumed biochemical pathways, the anoxic yields considered in the extended ASM2d can be obtained as a function of their respective aerobic yields. Thus, this modification does not mean an extra calibration effort to obtain the new parameters. In this work, an off-line calibration methodology has been applied to validate the model, where general relationships among stoichiometric parameters are proposed to avoid increasing the number of parameters to calibrate. The results have been validated through a UCT scheme pilot plant that is fed with municipal wastewater. The good concordance obtained between experimental and simulated values validates the use of anoxic yields as well as the calibration methodology. Deterministic modelling approaches, together with off-line calibration methodologies, are proposed to assist in decision-making about further process optimization in biological phosphate removal, since parameter values obtained by off-line calibration give valuable information about the activated sludge process such as the amount of DPAOs in the system.     

Crack detection in beam-like structures

Sensibility analysis of experimentally measured frequencies as a criterion for crack detection has been extensively used in the last decades due to its simplicity. However the inverse problem of the crack parameters (location and depth) determination is not straightforward. An efficient numerical technique is necessary to obtain significant results. Two approaches are herein presented: The solution of the inverse problem with a power series technique (PST) and the use of artificial neural networks (ANNs). Cracks in a cantilever Bernoulli–Euler (BE) beam and a rotating beam are detected by means of an algorithm that solves the governing vibration problem of the beam with the PST. The ANNs technique does not need a previous model, but a training set of data is required. It is applied to the crack detection in the cantilever beam with a transverse crack. The first methodology is very simple and straightforward, though no optimization is included. It yields relative small errors in both the location and depth detection. When using one network for the detection of the two parameters, the ANNs behave adequately. However better results are found when one ANN is used for each parameter. Finally, a combination between the two techniques is suggested.     

A model for chlorine concentration decay in pipes

A model that accounts for transport in the axial direction by convection and in the radial direction by diffusion and that incorporates first order decay kinetics has been developed to predict the chlorine concentration in a pipe in a distribution system. A generalized expression for chlorine consumption at the pipe wall is used to solve the governing equation and to determine the average chlorine concentration at any location in the pipe. Three non-dimensional parameters are used to determine the concentration and a methodology to determine them in pipe networks is proposed. The range of values of these dimensionless parameters where wall consumption is significant are determined. The methodology is applied to field measurements of chlorine concentration in a distribution network.     

Triple top line-based identification of sustainable water distribution system conservation targets and pipe replacement timing

ABSTRACT

This paper introduces a simulation-based sustainable life of pipe (SLP) determination for a water distribution system (WDS) using a triple top line (TTL) sustainability index (SI). SLP is the pipe replacement time maximizing SI. The approach is applied to the U-City system, a hypothetical urban WDS. Two case studies were conducted: (1) SLP to identify a conservation goal and (2) optimal SLP analysis using revised harmony search (ReHS) to discover replacement timing. The results show conservation targeting a 1% annual rate of demand growth maximizes the SI. And after optimizing the SLP, earlier pipe replacement and higher benefits result from the maximum SI approach compared to the least cost approach. In conclusion, the demonstrations show that using the TTL-based SI can guide demand management and pipe replacement strategies to maximize a comprehensive set of sustainability benefits.     

基于溶洞随机模型的岩质边坡稳定性评估研究

以城门山铜矿为例,提出了一种溶洞随机模型并将其应用于评估岩溶地区岩质边坡稳定性。钻孔数据统计表明溶洞长度分布服从负指数规律,而石灰岩长度分布是无规则的。基于钻孔数据,分别采用逆变换法和舍选法生成溶洞和石灰岩长度;同时,借鉴极限平衡法中竖直条分思路,将岩溶区域离散为有限数量的竖直条块;在此基础上,开发了溶洞随机模型生成软件。将溶洞随机模型导入极限平衡法,提出了一种岩溶地区岩质边坡稳定性评估方法。研究发现,溶洞随机模型模拟所得的溶洞特征参数与钻孔统计结果非常接近。考虑溶洞影响效应,城门山铜矿典型边坡的安全系数明显降低。该方法对于类似岩溶地区的溶洞分布模型构建以及岩质边坡稳定性评估具有重要的指导和推广意义。     

Sewer deterioration modeling with condition data lacking historical records

Accurate predictions of future conditions of sewer systems are needed for efficient rehabilitation planning. For this purpose, a range of sewer deterioration models has been proposed which can be improved by calibration with observed sewer condition data. However, if datasets lack historical records, calibration requires a combination of deterioration and sewer rehabilitation models, as the current state of the sewer network reflects the combined effect of both processes. Otherwise, physical sewer lifespans are overestimated as pipes in poor condition that were rehabilitated are no longer represented in the dataset. We therefore propose the combination of a sewer deterioration model with a simple rehabilitation model which can be calibrated with datasets lacking historical information. We use Bayesian inference for parameter estimation due to the limited information content of the data and limited identifiability of the model parameters. A sensitivity analysis gives an insight into the model's robustness against the uncertainty of the prior. The analysis reveals that the model results are principally sensitive to the means of the priors of specific model parameters, which should therefore be elicited with care. The importance sampling technique applied for the sensitivity analysis permitted efficient implementation for regional sensitivity analysis with reasonable computational outlay. Application of the combined model with both simulated and real data shows that it effectively compensates for the bias induced by a lack of historical data. Thus, the novel approach makes it possible to calibrate sewer pipe deterioration models even when historical condition records are lacking. Since at least some prior knowledge of the model parameters is available, the strength of Bayesian inference is particularly evident in the case of small datasets.     

Characterizing Heat Release Rates Using an Inverse Fire Modeling Technique

A ubiquitous source of uncertainty in fire modeling is specifying the proper heat release rate (HRR) for the fuel packages of interest. An inverse HRR calculation method is presented to determine an inverse HRR solution that satisfies measured temperature data. The methodology uses a predictor-corrected method and the Consolidated Model of Fire and Smoke Transport (CFAST) zone model to calculate hot gas layer (HGL) temperatures in single compartment configurations. The inverse method runs at super-real-time speeds while calculating an inverse HRR solution that reasonably matches the original HRR curve. Examples of the inverse method are demonstrated by using a multiple step HRR case, complex HRR curves, experimental temperature data with a constant HRR, and a case with an experimentally measured HRR. In principle, the methodology can be applied using any reasonably accurate fire model to invert for the HRR.     

Calibration of Structural Models Using Fuzzy Mathematics

Abstract: A calibration model is presented that quantifies the uncertainties associated with structural free vibration analysis. System identification objectives and fuzzy set mathematics are integrated to formulate an analysis methodology that enables the a priori prediction of the most probable sources of modeling error. By first developing fundamental fuzzy sets defining uncertainty in structural parameters such as stiffness and design loading, higher-level fuzzy sets governing dynamic behavior are obtained using the vertex method. Uncertainty in the dynamic parameters (natural frequency, frequency ratio, and structural response) are each represented using fuzzy mathematics, where membership functions are determined by performing multiple dynamic analyses involving confidence levels of model assumptions. A numerical example is presented to demonstrate the calibration model for a 13-story steel structure located in San Jose, California. Results show that the calibration model is capable of quantifying uncertainties in structural properties and behavior without requiring the measured data necessary for conventional system identification procedures.     

基于加权最小二乘法的供水管网节点流量校核

管网水力模型是实现供水系统现代化管理的重要工具,要使水力模型能比较准确地反映管网真实运行状态,达到预期使用目的,其中的参数需要校核。将管网节点流量校核作为优化问题,采用加权最小二乘法逐步迭代求解,与已有研究相比,采用矩阵分析法推导供水管网雅克比矩阵解析式,引入水量分配矩阵聚合节点流量,将欠定问题转化为超定,提高了校核的计算效率和结果的可靠性。采用简单管网阐明了雅克比矩阵的计算、节点流量的聚合及梯度向量的构造,利用实际管网验证了方法的实用性。     

Experimental strain analysis for polyethylene pipes installed by horizontal directional drilling

The results of five field tests on instrumented polyethylene (PE) pipes installed using horizontal directional drilling (HDD) are presented in the paper. The focus is on mechanical behavior of pipes, their stiffness, strength and deformations. The testing methodology is presented and correlation between different readings is discussed. The test results are presented in a form of pipe strains along the borepaths and vs. time of installation. The test program involved 200 mm (8 inch) diameter, standard dimension ratio (SDR) 17 and 150 mm (6 inch) diameter, SDR 11, high density and medium density polyethylene pipes pulled along 90 and 177 m borepaths. The parameters were the quality of the drilling fluids, the ratio of borehole to pipe diameters, pipe material, and construction sequence. The presented results show the variation of pipe strains with time and along the borepath. Strain gauge readings indicate both flexural and axial deformations. Included in the paper are also readings from a load cell indicating the value of the pulling force. The experimental results are analyzed in terms of different mechanisms that contribute to the increase of the pulling forces and straining of the pipe. Influence of the field test parameters is presented. Conclusions are drawn on the effects of the mechanisms and test parameters on the pipe mechanical behavior.     

Performance-based modelling of long-term deterioration to support rehabilitation and investment decisions in drinking water distribution systems

Managing the urban drinking water system in the long term in order to maintain system performance can be challenging due to the difficulty of modelling future deterioration of the networks. This paper establishes a methodology for cohort survival models where historical (empirical) data on decommissioning ages of pipes are used to calibrate survival functions of pipe cohorts according to service level targets. The benefit of the approach is that remaining useful life of pipes, future renewal rates and investment needs can be governed by a required level of service in the network. A case study shows how the methodology can be applied to a cohort of drinking water pipes to create a ‘calibration curve’, which is a survival function calibrated with empirical data.     

Metabolic modelling of full-scale biological nitrogen and phosphorus removing wwtp's.

This paper evaluates the experiences with modelling full-scale biological phosphorus and nitrogen removing wastewater treatment plants. For the simulation, we used a metabolic phosphorus model integrated in ASM2d, further referred to as TUDP-model. It was found that the metabolic model for bio-P removal can be applied for modelling full-scale wwtp's, without extensive parameter adjustments. A stepwise modelling approach was proposed. Only three specific parameters were calibrated. Two parameters, the inert fraction in the influent and the actual anoxic sludge fraction will need calibration for all systems. Parameter sensitivity analyses showed that the sensitivity of operational data, often considered as known input data, is high. The model kinetics were found less sensitive. This will in general be the case for all low-loaded wwtp's recorded in their pseudo-steady state. Based on mass balance calculations, operational data and measurements were evaluated. Since all terms on a phosphorus balance can be measured, errors in operational data (e.g. SRT and flow rates) become very apparent in P-removal models (ASM2d, TUDP). We suggest using the P-balance in general for wwtp modelling, as a check on data consistency. This study showed that considering operational data per definition as known input data is not justified. Therefore, operational data should be evaluated, or considered in model calibration over the use of kinetic and stoichiometric parameters.     

A high resolution application of a stormwater management model (SWMM) using genetic parameter optimization

Low Impact Development (LID) tools and green infrastructure approaches have been developed and applied to mitigate the urbanization impacts on increasing runoff and pollutant washoff. The present work is the first part of a larger effort to simulate LID scenarios for a large scale urban catchment through up-scaling of high-resolution study catchments using the Stormwater Management Model (SWMM). In this study we present the setup, calibration, validation, and the results of a parameter sensitivity analysis of a high-resolution SWMM model for a highly urbanized small catchment located in Southern Finland. The homogenous subcatchments and associated narrow parameter boundaries, which are allowed by the high spatial resolution, result in insensitivity of SWMM to the fraction of impervious cover. The model optimization, using only the two identified key parameters “depression storage” and “Manning's roughness n for conduit flow”, yielded good performance statistics for both calibration and validation of the model.     

基于ARC/INFO的城市管网信息系统的设计与建立

对城市管网信息系统的设计与开发从系统的总体设计、系统的功能结构、系统的实现等多方面进行了详细的探讨 ,建立了城市管网信息系统模型 ,并根据这个模型建立了大连市管网信息系统 ,从而为其它城市建立城市管网信息系统和其它类似的系统提供了一个值得借鉴范例。