Tiit Koppel

A review of methods for leakage management in pipe networks

Leakage in water distribution systems is an important issue which is affecting water companies and their customers worldwide. It is therefore no surprise that it has attracted a lot of attention by both practitioners and researchers over the past years. Most of the leakage management related methods developed so far can be broadly classified as follows: (1) leakage assessment methods which are focusing on quantifying the amount of water lost; (2) leakage detection methods which are primarily concerned with the detection of leakage hotspots and (3) leakage control models which are focused on the effective control of current and future leakage levels. This paper provides a comprehensive review of the above methods with the objective to identify the current state-of-the-art in the field and to then make recommendations for future work. The review ends with the main conclusion that despite all the advancements made in the past, there is still a lot of scope and need for further work, especially in area of real-time models for pipe networks which should enable fusion of leakage detection, assessment and control methods.

Calibration of a model of an operational water distribution system containing pipes of different age

The aim of the paper is to demonstrate that the Levenberg-Marquardt algorithm can give successful results when operational water distribution systems are calibrated with the proper selection of parameter increment for the calculation of partial derivatives. The functional dependence of pipe roughness on age, which describes linear and nonlinear dependences, is proposed for the calibration of a model of a water distribution system containing pipes of different age. It is also shown that the visualization of response surface on a coarse grid is very useful for the analysis of the results.

PROBABILISTIC LEAK DETECTION IN PIPE NETWORKS USING THE SCEM-UA ALGORITHM

Several methods have been developed so far which attempt to detect leaks in water distribution systems by taking into account pressure (and possibly other available) measurements. As in many previous approaches, the leak detection problem is formulated and solved here as an inverse problem with unknown leak areas being the calibration parameters. However, unlike the previous approaches, a stochastic (rather than deterministic) leakage detection methodology is developed and used here. This methodology is based on the Shuffled Complex Evolution Metropolis (SCEM-UA) algorithm and is capable of estimating the posterior probability density functions of unknown leak areas in a single model run. Baring in mind the accuracy of similar leak detection approaches, it is believed that the stochastic context used here is more appropriate than the deterministic one used before. To achieve the above goal, the Epanet2 hydraulic network modelling software is linked to the SCEM-UA software in the Matlab programming environment. The SCEM-UA algorithm parameters are tuned to achieve an effective and efficient search for unknown leak areas. The methodology developed is tested on two literature case studies.

Experimental investigation on rapid filling of a large-scale pipeline

This study presents the results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water-level meters, thermometers, void fraction meters, and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water-air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made.

Emptying of large-scale pipeline by pressurized air

AbstractEmptying of an initially water-filled horizontal PVC pipeline driven by different upstream compressed air pressures and with different outflow restriction conditions, with motion of an air-water front through the pressurized pipeline, is investigated experimentally. Simple numerical modeling is used to interpret the results, especially the observed additional shortening of the moving full water column due to formation of a stratified water-air “tail.” Measured discharges, water-level changes, and pressure variations along the pipeline during emptying are compared using control volume (CV) model results. The CV model solutions for a nonstratified case are shown to be delayed as compared with the actual measured changes of flow rate, pressure, and water level. But by considering water-column mass loss due to the water-air tail and residual motion, the calibrated CV model yields solutions that are qualitatively in good agreement with the experimental results. A key interpretation is that the long air...

HYDRAULIC POWER ANALYSIS FOR DETERMINATION OF CHARACTERISTICS OF A WATER DISTRIBUTION SYSTEM

A water distribution system which consists of distribution network and pumping station is considered. The global energy performance and hydraulic power capacity of the water distribution network is analysed. The energetically maximum flows in pipes and networks are determined. The coefficient of output power efficiency and the surplus power factor of hydraulic systems are defined. The assemblage of characteristic curves of water distribution network is analysed from the aspect of energetically maximum flows in network.

Use of modelling error dynamics for the calibration of water distribution systems

The calibration of a water distribution system remains a complex task. Leakages create additional difficulties if their proportion is high. Not all leakages are real. A part of them are apparent leakages. An optimization procedure is proposed to obtain the proportions of real and apparent leakages. The distribution of the leakages over a WDS may be made easier by analyzing the dependence of modelling errors on water flow. It is suggested that pressure measurements should be ranked according to the closeness of measurement to the water source and that modelling errors should be analysed separately for the measurements of different order (from the first to the highest). The advantage of this approach is that the analysis is confined within points of measurements of one order and it allows to redistribute fluxes of leakages (real and apparent) more reliably. Nonlinear optimization with linear constraints is used for the redistribution of leakages over a WDS. The methodology proposed allows to exclude the influence of systematic errors on the result of calibration.

Estimation of real-time demands on the basis of pressure measurements by different optimization methods

The aim was to estimate real-time demands in a water distribution system on the basis of pressure measurements. The task was formulated as an optimization procedure to find water flows correcting typical demands that will minimize differences between measured and modelled pressures. The Levenberg-Marquardt algorithm (LMA) and the Genetic algorithm (GA) were tested to solve the problem. Results showed that the LMA works much faster than the GA. It was also found that the higher the demands the lower is the sensitivity of the results to random errors in pressure measurements. Measurements in an operational WDS were used in calculations.

Real-time demands and calibration of water distribution systems

All computer models of water distribution systems (WDS) have to contain information about demands. Usually demands are derived based on customers water meters weekly or monthly readings. It gives information only about the average demand. Dynamics of hourly, daily and weekly demands are usually estimated based on typical demand patterns of different type of consumer groups like domestic households, hospitals or hotels. Estimation of demand dynamics by this manner inevitably decreases precision of calibration. Calculations show that differences between real-time and typical demand can influence results of calibration. The paper proposes some methods to minimize this influence. Special software has been developed for estimation of real-time water demands in a WDS. Algorithms and software checked on an operational WDS.

Estimation of real-time water fluxes in water distribution system on the basis of pressure measurements

Experience in calibration of water distribution system (WDS) models shows large uncertainties of demands estimated on the basis of typical hourly values for different types of consumers. The typical dynamics of demands, which are used for the lack of more detailed information, differ from real-time demands in time and in space. It makes it difficult to estimate real-time water fluxes in WDS which are necessary for evaluation of the propagation rate of the contaminated zones in case of deliberate or accidental chemical or biological threats. The aim of this investigation was to test the possibility of estimating real-time water flow fluxes in District Meter Areas (DMAs) on the basis of pressure measurements. Results have been tested on the operational WDS.