Inverse Transient Analysis Research Articles

Leak detection in pipelines by inverse backward transient analysis

A new method of leak detection in pipelines is introduced based on the inverse transient analysis. The transient state can be initiated in pipes by closing the downstream end valve. The time history of pressure fluctuations is measured at the valve location as a downstream boundary condition. The duration of valve closure is considered long enough to minimize effects of the friction factor and of waterhammer. The numerical modeling of transient analysis in time domain uses the backward Method Of Characteristics (MOC).An inverse problem is applied for leak detection by defining the least-squares criterion objective function. The leak areas at characteristic nodes are considered as decision variables. Leak parameters are determined using the Sequential Quadratic Programming (SQP) method. To eliminate undesirable noisy and uncertainties due to the valve modeling, a method independent of valve type, closure duration and valve operation was considered. Finally, numerical examples are solved based on this method.

A Simulation Study on Using Inverse Transient Analysis for Leak Detection in Water Distribution Networks

Inverse transient analysis, developed by several researchers in recent years as a promising and low-cost leak detection technique, has been successfully demons…

Three-dimensional inverse transient heat transfer analysis of thick functionally graded plates

In this paper, a three-dimensional transient inverse heat conduction (IHC) procedure is presented to estimate the unknown boundary heat flux of thick functionally graded (FG) plates. For this purpose, the conjugate gradient method (CGM) in conjunction with adjoint problem is used. A recently developed three-dimensional efficient hybrid method is employed to solve variable-coefficient initial-boundary-value differential equations of direct problem as a part of the inverse solution. The accuracy of the inverse analysis is examined by simulating the exact and noisy data for problems with different types of boundary conditions and material properties. In addition to rectangular domain, skew plates are considered. The results obtained show good accuracy for the estimation of boundary heat fluxes.

Leak detection in pipelines by inverse backward transient analysis

Leak detection in pipelines by inverse backward transient analysis

Systematic exploration of pipeline network calibration using transients

Accurate information of pipeline and system properties is crucially important for precise computer simulation of pipe networks. Even though inverse transient analysis (ITA) techniques have been widely investigated for leak detection and friction factor calibration, many challenges still remain. One reason for these difficulties is that real water distribution systems invariably have many kinds of uncertainties including pipe diameter, wave speed and the water demand at the time of the tests. This paper investigates quantitatively how inaccuracies in such values invariably deteriorate the performance of calibration approaches. Thus, the paper argues that a systematic calibration should explicitly include these additional uncertainties during the ITA process. Two evolutionary approaches, namely Genetic Algorithms and Particle Swarm Optimization, are applied and are both compared and contrasted during the ITA iterations. The evolutionary algorithms help the search escape from poor local optima in multifaceted and complex problems and thus assist in locating global (or near-global) optima. However, most current approaches are shown to converge poorly as the full scale of the typical field problems is progressively reflected in the search space.

Experimental Observation and Analysis of Inverse Transients for Pipeline Leak Detection

Fluid transients result in a substantial amount of data as pressure waves propagate throughout pipes. A new generation of leak detection and pipe roughness calibration techniques has arisen to exploit those data. Using the interactions of transient waves with leaks, the detection, location, and quantification of leakage using a combination of transient analysis and inverse mathematics is possible using inverse transient analysis (ITA). This paper presents further development of ITA and experimental observations for leak detection in a laboratory pipeline. The effects of data and model error on ITA results have been explored including strategies to minimize their effects using model error compensation techniques and ITA implementation approaches. The shape of the transient is important for successful application of ITA. A rapid input transient (which may be of small magnitude) contains maximum system response information, thus improving the uniqueness and quality of the ITA solution. The effect of using head measurements as boundary conditions for ITA has been shown to significantly reduce sensitivity, making both detection and quantification problematic. Model parsimony is used to limit the number of unknown leak candidates in ITA, thus reducing the minimization problem complexity. Experimental observations in a laboratory pipeline confirm the analysis and illustrate successful detection and quantification of both single and multiple leaks.

Numerical Error in Weighting Function-Based Unsteady Friction Models for Pipe Transients

The accurate simulation of pressure transients in pipelines and pipe networks is becoming increasingly important in water engineering. Applications such as inverse transient analysis for condition assessment, leak detection, and pipe roughness calibration require accurate modeling of transients for longer simulation periods that, in many situations, requires improved modeling of unsteady frictional behavior. In addition, the numerical algorithm used for unsteady friction should be highly efficient, as inverse analysis requires the transient model to be run many times. A popular model of unsteady friction that is applicable to a short-duration transient event type is the weighting function-based type, as first derived by Zielke in 1968. Approximation of the weighting function with a sum of exponential terms allows for a considerable increase in computation speed using recursive algorithms. A neglected topic in the application of such models is evaluation of numerical error. This paper presents a discussion and quantification of the numerical errors that occur when using weighting function-based models for the simulation of unsteady friction in pipe transients. Comparisons of numerical error arising from approximations are made in the Fourier domain where exact solutions can be determined. Additionally, the relative impor- tance of error in unsteady friction modeling and unsteady friction itself in the context of general simulation is discussed.

Transient Analysis and Leakage Detection Algorithm using GA and HS algorithm for a Pipeline System

The impact of leakage was incorporated into the transfer functions of the complex head and discharge. The impedance transfer functions for the various leaking pipeline systems were also derived. Hydraulic transients could be efficiently analyzed by the developed method. The simulation of normalized pressure variation using the method of characteristics and the impulse response method shows good agreement to the condition of turbulent flow. The leak calibration could be performed by incorporation of the impulse response method with Genetic Algorithm (GA) and Harmony Search (HS). The objective functions for the leakage detection can be made using the pressure-head response at the valve, or the pressure-head or the flow response at a certain point of the pipeline located upstream from the valve. The proposed method is not constrained by the Courant number to control the numerical dissipation of the method of charac teristics. The limitations associated with the discreteness of the pipeline system in the inverse transient analysis can be neglected in the proposed method.

Application of hydraulic transients for leak detection in water supply systems

The current paper reports the investigation of two transient-based techniques for leak detection in water pipe systems using physical data collected in the laboratory and in quasi-field conditions. The first is the analysis of the leak reflected wave during a transient event and the second is inverse transient analysis (ITA). This was approached through the development of an inverse transient analysis tool and the collection of transient data for the testing and validation of this model. Two experimental programmes were carried out at Imperial College and in cooperation with Thames Water for the validation and testing of these techniques. Evaluation of the presence, location and size of leaks was carried out using the collected data. Transient-based techniques have been shown to be successful in the detection and location of leaks and leak location uncertainties depended on the leak size and location, flow regime and location where the transient event was generated. These leak detection methods are very promising for identifying the general area of the trunk main with leakage, and can be combined with other leak location techniques (e.g. acoustic equipment) to more precisely pinpoint the leak position. Transient-based techniques are particularly important for the diagnosis, monitoring and control of existing water supply systems, not only to detect leaks, but also to better understand the causes of pipe bursts and accidents, particularly when these are due to natural transient events.

Discussion and Closure: Inverse Transient Analysis in Pipe Networks

Discussion and Closure: Inverse Transient Analysis in Pipe Networks

Closure to “Inverse Transient Analysis in Pipe Networks” by James A. Liggett and Li-Chung Chen

Closure to “Inverse Transient Analysis in Pipe Networks” by James A. Liggett and Li-Chung Chen