Inverse Transient Analysis Research Articles

Faster Inverse Transient Analysis with a Head-Based Method of Characteristics and a Flexible Computational Grid for Pipeline Condition Assessment

AbstractTargeted and proactive pipeline condition assessment is critical for cost-effective maintenance of aging water transmission and distribution systems. The current research proposes a fast in...

Leak Detection in a Branched System by Inverse Transient Analysis with the Admittance Matrix Method

The diagnosis of water distribution systems by means of the inverse transient analysis requires efficient and reliable numerical models. In the network admittance matrix method (NAMM) the 1-D waterhammer governing equations are integrated in the frequency domain and organized in a laplacian matrix form. The NAMM is particularly suitable for complex systems because of this structure and can be used for the system diagnosis, including leak sizing and location. In this paper a damaged branched system is considered and the diagnosis is performed by means of the NAMM using experimental data from laboratory transient tests. Two different boundary conditions are used in the implementation of the NAMM and the leak is located and sized with a reasonable approximation. An extended numerical investigation is also presented and allows confirmation of the results for different leak locations. The use of the NAMM for the leak detection and the validation using experimental data on a branched system are the main original contributions of this work. The successful diagnosis indicates promising results for applications in more complex systems.

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.

Inverse Transient Radiative Analysis in Two-Dimensional Turbid Media by Particle Swarm Optimizations

Three intelligent optimization algorithms, namely, the standard Particle Swarm Optimization (PSO), the Stochastic Particle Swarm Optimization (SPSO), and the hybrid Differential Evolution-Particle Swarm Optimization (DE-PSO), were applied to solve the inverse transient radiation problem in two-dimensional (2D) turbid media irradiated by the short pulse laser. The time-resolved radiative intensity signals simulated by finite volume method (FVM) were served as input for the inverse analysis. The sensitivities of the time-resolved radiation signals to the geometric parameters of the circular inclusions were also investigated. To illustrate the performance of these PSO algorithms, the optical properties, the size, and location of the circular inclusion were retrieved, respectively. The results showed that all these radiative parameters could be estimated accurately, even with noisy data. Compared with the PSO algorithm with inertia weights, the SPSO and DE-PSO algorithm were demonstrated to be more effective and robust, which had the potential to be implemented in 2D transient radiative transfer inverse problems.

A review of methods for burst/leakage detection and location in water distribution systems

The problem of bursts and leakages in water distribution systems has received significantly increased attention over the past two decades. As they represent both an environmental and an economical issue, how to reduce water loss through bursts and leakages is a challenging task for water utilities. Consequently, various techniques have been developed to detect the location and size of leakages. The methods for bursts (or leaks) detection and location can be broadly divided into two main categories, one based on hardware and the other based on software. Hardware-based methods include (i) acoustic detection methods such as listening rods, leak correlators, leak noise loggers and (ii) non-acoustic detection methods such as gas injection, ground penetrating radar technology and infrared photography. Software-based methods make use of the data collected by real-time pressure and/or flow sensors and several artificial intelligence techniques and statistical data analysis tools, including (i) methods based on numerical modeling methods, such as inverse transient analysis, time domain analysis and frequency domain analysis, and (ii) some non-numerical modeling methods, such as artificial neural networks, Bayesian inference systems, the Golden section method, and Kalman filtering. In this article, the authors describe the methods for pipe network burst location and detection, summarize the features of each method, and propose a suggestion for future work.

Straightforward Transient-Based Approach for the Creep Function Determination in Viscoelastic Pipes

This work introduces a simple and straightforward approach for the creep function determination in viscoelastic pipes on the basis of transient flow analysis. The governing equations are expanded and analytically solved for the first half period of the transient. This solution results in a direct formula for the viscoelastic Joukowsky pressure head as a function of the creep function coefficients which are a priori unknown. Utilizing the measured data, only in the first half water hammer period and the proposed viscoelastic Joukowsky formula, the problem unknowns are determined. To investigate the method’s merits and limitations, two experimental polyethylene pipes are taken into account from the literature. The results show that the proposed approach works very well for long enough pipelines which are completely crept in the half period of the transient flow. The method is found to be computationally efficient and easy to implement in comparison with traditional inverse transient analysis techniques.

Energy dissipation and pressure decay during transients in viscoelastic pipes with an in-line valve

In this paper, the effect of a partially closed in-line valve, viscoelasticity, and unsteady friction on the transient behavior of a pressurized pipe is examined. Such an analysis is executed by considering global energy quantities evaluated by means of a one-dimensional numerical model calibrated on the basis of a huge amount of laboratory tests. In the numerical experiments, the effect of the initial conditions and in-line valve characteristics has been analyzed by considering different values of the initial Reynolds number, N0, in-line valve head loss coefficient, χ, and location, δ. By introducing dimensionless quantities, exponential laws are shown to interpolate the time-history of maxima of both pressure and global energy quantities reliably with the related coefficients being a function of N0, χ, and δ. Thus, the links between the decay of pressure peaks at single sections and the dissipation of the global kinetic and internal energy are established. Moreover, it is shown that a given decay of pressure peaks may derive from very different transients. This result has crucial implications to inverse transient analysis based on the evaluation of the pressure decay at a given section with particular attention to the uniqueness of the solution.

Inverse Transient Analysis for a Branched Pipeline System with Leakage and Blockage Using Impedance Method

Abstract In this study, analytical expressions for pressure head and discharge in the frequency domain were presented for a branched pipeline system with both a leakage and a blockage. To consider the unsteady friction's impact, the impedance development process implemented both unsteady friction impact resulting from velocity profiles with two-dimensional distributions and unsteady friction resulting from acceleration. Based on impedance expressions defining this system, response functions were derived in the frequency domain and their corresponding time-domain responses were integrated into a meta-heuristic calibration scheme for inverse transient analysis.

Holistic Diagnosis of Pipeline System with Impedance Method

In this study, a diagnosis potential of impedance method implementing several unsteady friction models for a pipeline system with or without leakage. The development based on impedance approach provides a feasible and flexible modelling environment that can address not only for various fundamental system properties, but also for dynamic variables in transient generation. Calibration parameters cover conventional diagnostic parameters such as friction parameters and leakage, steady and transient condition parameters such as the initial flow rate and valve closure duration, and system characteristics such as pipeline length and wave propagation speed. Based on the perspective of the impedance for system definition, corresponding response functions in the frequency domain approach were derived. Time domain responses of pipeline systems were integrated into the genetic algorithm for inverse transient analysis. Unsteady models addressed both frequency-dependent friction and acceleration-based frictions. Parameter calibrations with experimental data have shown that the impedance-based approach provides a versatile and feasible optimization structure via the objective fitting function of the pressure head variation. The performance of the integrated optimization examples demonstrates the robustness of the impedance-based approach for a representation of a real-life system, a diagnosis of system abnormality and a configuration of system characteristics.

Inverse Transient Analysis for Classification of Wall Thickness Variations in Pipelines

Analysis of transient fluid pressure signals has been investigated as an alternative method of fault detection in pipeline systems and has shown promise in both laboratory and field trials. The advantage of the method is that it can potentially provide a fast and cost effective means of locating faults such as leaks, blockages and pipeline wall degradation within a pipeline while the system remains fully operational. The only requirement is that high speed pressure sensors are placed in contact with the fluid. Further development of the method requires detailed numerical models and enhanced understanding of transient flow within a pipeline where variations in pipeline condition and geometry occur. One such variation commonly encountered is the degradation or thinning of pipe walls, which can increase the susceptible of a pipeline to leak development. This paper aims to improve transient-based fault detection methods by investigating how changes in pipe wall thickness will affect the transient behaviour of a system; this is done through the analysis of laboratory experiments. The laboratory experiments are carried out on a stainless steel pipeline of constant outside diameter, into which a pipe section of variable wall thickness is inserted. In order to detect the location and severity of these changes in wall conditions within the laboratory system an inverse transient analysis procedure is employed which considers independent variations in wavespeed and diameter. Inverse transient analyses are carried out using a genetic algorithm optimisation routine to match the response from a one-dimensional method of characteristics transient model to the experimental time domain pressure responses. The accuracy of the detection technique is evaluated and benefits associated with various simplifying assumptions and simulation run times are investigated. It is found that for the case investigated, changes in the wavespeed and nominal diameter of the pipeline are both important to the accuracy of the inverse analysis procedure and can be used to differentiate the observed transient behaviour caused by changes in wall thickness from that caused by other known faults such as leaks. Further application of the method to real pipelines is discussed.

Inverse transient radiation analysis in one-dimensional participating slab using improved Ant Colony Optimization algorithms

As a heuristic intelligent optimization algorithm, the Ant Colony Optimization (ACO) algorithm was applied to the inverse problem of a one-dimensional (1-D) transient radiative transfer in present study. To illustrate the performance of this algorithm, the optical thickness and scattering albedo of the 1-D participating slab medium were retrieved simultaneously. The radiative reflectance simulated by Monte-Carlo Method (MCM) and Finite Volume Method (FVM) were used as measured and estimated value for the inverse analysis, respectively. To improve the accuracy and efficiency of the Basic Ant Colony Optimization (BACO) algorithm, three improved ACO algorithms, i.e., the Region Ant Colony Optimization algorithm (RACO), Stochastic Ant Colony Optimization algorithm (SACO) and Homogeneous Ant Colony Optimization algorithm (HACO), were developed. By the HACO algorithm presented, the radiative parameters could be estimated accurately, even with noisy data. In conclusion, the HACO algorithm is demonstrated to be effective and robust, which had the potential to be implemented in various fields of inverse radiation problems.

Discussion of “Case Studies of Leak Detection and Location in Water Pipe Systems by Inverse Transient Analysis” by Dídia Covas and Helena Ramos

In a lecture about fundamental issues in numerical hydraulicsgiven within the theme “Frontiers in Hydraulics: ComputationalHydraulics” of the Iowa Hydraulics Colloquium, Liggett (1996)indicated the solution of transient flow in networks as a problemthat had not been studied as intensively as many other hydraulicsproblems. Moreover, Liggett voted for inverse analysis as thenext big push in numerical hydraulics. In the discussers’ opinion,this paper not only gives a valuable contribution in the field oftransient test-based techniques (TTBT) for simple pipe systemdiagnosis but also points out some crucial aspects that couldbe investigated more extensively. Precisely, to improve the per-formance of TTBT for the detection of possible anomalies(e.g., leaks, partial blockages, partially closed in-line valves,and illegal branches), the following questions arise: (1) why notcouple the ITA approach with a preliminary analysis of transientpressure data? and (2) why not generate controlled and sharppressure waves by means of proper devices instead of by maneu-vering valves?With regard to the first question, some benefits could beachieved by first locating the anomalies by analyzing the timehistory of the pressure (i.e., pressure signal,

Determining the Internal Wall Condition of a Water Pipeline in the Field Using an Inverse Transient

The application of inverse transient analysis (ITA) to estimate the location and magnitude of lost lining and internal corrosion of metal pipelines is demonstrated for a field pipeline. The method uses a transient model and inverse search algorithm to analyze patterns of measured pressure reflections obtained after a transient pressure wave is induced in a pipeline. The method is applied in the field on a 6 km long section of a 750 mm nominal diameter steel pipeline with internal cement mortar lining. The equipment used for generating hydraulic transients and measuring pressure responses in the pipeline is described. Results of the field tests are analyzed to estimate the location and extent of internal wall damage along the pipeline. Extensive ultrasonic thickness survey results are used to corroborate the approximate location and magnitude of predicted pipeline wall damage.

Detection of Leakage Freshwater and Friction Factor Calibration in Drinking Networks Using Central Force Optimization

Inverse Transient Analysis (ITA) is a powerful approach for leak detection and calibration of friction factors in pressurized pipes. Through this method, a transient flow is initiated and pressures are measured somewhere in the system. Then, a nonlinear programming (NLP) problem with a least-squares criterion objective function is developed to minimize discrepancies between the measured and calculated pressures at measurement sites. Solving the raised NLP results in the problem’s unknowns being leakage specifications and pipe friction factors. For this purpose, various optimization techniques may be utilized. This issue is a major challenge for ITA-based methods. The present work aims at applying the new method of Central Force Optimization (CFO) to the problem of ITA. CFO is a deterministic metaheuristic inspired by gravitational kinematics in which small objects in space are dragged by bigger ones. Herein, the concept and main structure of CFO are represented as well as of CFO. A reference pipe-network is considered to be solved using the ITA equipped with CFO. The results are then discussed compared to the previous works. It is concluded that CFO is easy to implement, computationally efficient and has a remarkable performance in solving leak detection problem.

Two-Dimensional Inverse Transient Heat Conduction Analysis of Laminated Functionally Graded Circular Plates

A two-dimensional inverse transient heat conduction algorithm is developed to estimate the heat flux and convection heat transfer coefficient on the bottom (top) surface of the multilayered functionally graded (FG) circular plates using the measured temperature on their top (bottom) surface. The non-Fourier heat transfer, in conjunction with the layerwise-incremental differential quadrature method (LW-IDQM), is employed to accurately model the problem. The conjugate gradient method (CGM), coupled with the sensitivity and adjoint problems, are employed for the optimization procedure. The reliability and robustness of the presented approach is demonstrated by simulating the exact and noisy data through different examples.

Inverse transient radiation analysis in one-dimensional non-homogeneous participating slabs using particle swarm optimization algorithms

Particle Swarm Optimization (PSO) algorithms, including standard PSO, Stochastic PSO, and Multi-Phase PSO, are applied to solve the time-domain inverse transient radiation problems in the present research. Time-resolved transmittance and reflectance signals of four different measuring models serve as the measurement data, which estimate absorption, scattering coefficients, and geometric position within one-dimensional non-homogeneous media by inverse simulation. To check retrieval performances and accuracies of PSO-based approaches, four different inverse transient radiation cases are investigated to deal with one homogeneous layer, two-layer, three-layer, and continuous non-homogenous media. The influences of different searching ranges, swarm sizes, and maximum fly velocities on the fitness function of PSO are discussed. Meanwhile, the effects of measurement errors on the reconstruction accuracy are also investigated. All the results confirm that radiative parameters could be estimated accurately with measurement noise using PSO-based approaches.

Transient generation in pipe networks for leak detection

Inverse transient analysis is known to be a powerful approach for leak detection and calibration of friction factors in pressurised pipes. In order to use inverse transient analysis, a transient state is generated in the system by opening or closing a regulating valve. This excitation and its location in a pipe network significantly influence the success of inverse-transient-analysis-based methods; this issue is the focus of this work. The paper defines a mathematical programming model to produce rapid transient variations in the system subject to allowable high and low pressures. The transient generation point in the network, the time interval and the magnitude of the excitation are decision variables. Using the method of characteristics, a numerical model is developed to analyse transients and evaluate the objective function. Based on genetic algorithms, an optimisation solver is developed to solve the problem. To demonstrate the efficiency of the method, a water distribution network of 34 pipes (with unknown friction factors) and 22 junctions (with unknown leaks) is defined and analysed. The results show that the proposed method makes a remarkable contribution to the success of applied inverse transient analysis.

Leak detection by inverse transient analysis in an experimental PVC pipe system

Leakage reduction in water supply systems and distribution networks has been an increasingly important issue in the water industry since leaks and ruptures result in major physical and economic losses. Hydraulic transient solvers can be used in the system operational diagnosis, namely for leak detection purposes, due to their capability to describe the dynamic behaviour of the systems and to provide substantial amounts of data. In this research work, the association of hydraulic transient analysis with an optimisation model, through inverse transient analysis (ITA), has been used for leak detection and its location in an experimental facility containing PVC pipes. Observed transient pressure data have been used for testing ITA. A key factor for the success of the leak detection technique used is the accurate calibration of the transient solver, namely adequate boundary conditions and the description of energy dissipation effects since PVC pipes are characterised by a viscoelastic mechanical response. Results have shown that leaks were located with an accuracy between 4–15% of the total length of the pipeline, depending on the discretisation of the system model.

Optimum leak detection and calibration of pipe networks by inverse transient analysis

Inverse transient analysis is known as a powerful approach for leak detection and calibration of pipe networks. This work aims to introduce new features to carry out this analysis more efficiently. An optimization programming is developed to generate transients in the network optimally, and then pressure fluctuations are sampled at a few optimum measurement sites. Criteria are introduced for optimum site design. A non-linear programming with the least squares criterion is defined and then the unknown parameters of leaks and friction factors are inversely sought using sequential quadratic programming. A theoretical demonstrative example is also presented and solved using the method in which the obtained results show how the proposed new features make the process of leak detection more effective.

Case Studies of Leak Detection and Location in Water Pipe Systems by Inverse Transient Analysis

The current paper aims at the assessment of the effectiveness of a popular transient-based technique—inverse transient analysis (ITA)—for leak detection in water pipe systems using physical data. Data were collected from two pipe systems made of polyethylene: a laboratory facility at Imperial College London and a quasi-field system at Thames Water Utilities. A hydraulic transient solver especially developed for viscoelastic pipes (typically made of polyethylene) and an optimization algorithm for the simultaneous creep calibration and leak location have been developed for the application of this technique. The evaluation of the presence, location, and size of leaks was carried out using collected data. ITA allowed for the identification of the approximate location of leaks as long as the physical characteristics of the pipeline are well known, the transient is generated by a fast change of flow conditions, the leak has a “reasonable size,” and the transient solver is accurate enough to describe the transie...