Parameters affecting water-hammer wave attenuation, shape and timing—Part 2: Case studies (original) (raw)
Related papers
Parameters affecting water-hammer wave attenuation, shape and timing—Part 1: Mathematical tools
Journal of Hydraulic Research, 2008
This two-part paper investigates key parameters that may affect the pressurewaveform predicted by the classical theory ofwater-hammer. Shortcomings in the prediction of pressure wave attenuation, shape and timing originate from violation of assumptions made in the derivation of the classical waterhammer equations. Possible mechanisms that may significantly affect pressure waveforms include unsteady friction, cavitation (including column separation and trapped air
2003
This paper further investigates parameters that may affect water hammer wave attenuation, shape and timing . New sources that may affect the waveform predicted by classical water hammer theory include viscoelastic behaviour of the pipe-wall material, blockage and leakage in addition to the previously discussed unsteady friction, cavitation and fluid-structure interaction. These discrepancies are based on the same basic assumptions used in the derivation of the water hammer equations for the liquid unsteady pipe flow, i.e. the flow is considered to be one-dimensional (cross-sectionally averaged velocity and pressure distributions), the pressure is higher than the liquid vapour pressure, the pipe-wall and liquid have a linear-elastic behaviour, unsteady friction losses are approximated as steady state losses, the amount of free gas in the liquid is negligible, fluidstructure coupling is weak (precursor wave pressure changes are much smaller than the water hammer pressures), the pipe is straight and of uniform shape (no blockage) and there is no lateral outflow (leakage) or inflow (pollution).
Wave Speed Calculation For Water Hammer Analysis
Cálculo de la velocidad de onda para el análisis del golpe de ariete Fecha de entrega: 13 de mayo 2016 Fecha de aceptación: 7 de noviembre 2016 In order to accurately solve the water hammer problem using the Method of the Characteristics MOC is necessary to fulfil with the so−called Courant condition which establishes mandatorily that C n = f(a) = 1 in each pipeline of the system, where a is the wave speed. The value of C n is dependant of a whose value depends in turn on the fluid properties (density, bulk modulus) and physical characteristics of each pipeline (elasticity modulus, diameter, wall thickness, supporting condition). Because water distribution systems usually has many different pipes, and therefore, many different wave speeds, it can be said that fulfil with C n = 1 in each pipeline is a very difficult task, more when the solution by MOC needs a common time step Δt for all pipe sections of the system. A way of solution to this problem is applying the method of the wave−speed adjustment that involves modifying the value of a in each pipe section in a certain percentage up to obtain C n = 1. With this procedure optimum results are guaranteed in numerical terms, but it is possible to say the same in physical terms? The question which arises is: what parameters within the formula of a must (or can) be changed without exceeding the characteristic values of the component material of the pipes?. This work shows that in some cases the wave speed modification can significantly alter the value of the parameters that define a, leading to values that can be physically inconsistent, fictitious or without practical application. Keywords: wave speed, water hammer, Courant number Para resolver en forma precisa el problema de golpe de ariete usando el Método de las Características MC es necesario que el número de Courant C n = 1 en cada tubería del sistema. El valor de C n depende de la velocidad de la onda a, cuyo valor depende a su vez de las propiedades del fluido (densidad, módulo de compresión) y de las características físicas de cada tubería (módulo de elasticidad, diámetro, espesor, condición de apoyo). Debido a que las redes de distribución de agua generalmente tienen muchas tuberías diferentes, y por tanto, muchas velocidades de onda distintas, cumplir con C n = 1 en cada tubería se torna una tarea muy difícil, más aún cuando la solución mediante el MC necesita un paso de tiempo Δt común para todas las tuberías del sistema. Una forma de solución a este problema es aplicar el método de ajuste de la velocidad de la onda que consiste en modificar el valor de a en cada tubería en un cierto porcentaje hasta obtener C n = 1. Con esto se garantizan resultados óptimos en términos numéricos, pero ¿es posible decir lo mismo en términos físicos?. La pregunta que se plantea es: ¿qué parámetros dentro de la fórmula de a deben (o pueden) ser cambiados sin exceder los valores característicos del material componente de la tubería?. En este trabajo se muestran algunos casos donde la modificación de a puede alterar significativamente la magnitud de los parámetros que definen su valor, dando lugar a valores que pueden ser físicamente incompatibles, ficticios o sin aplicación práctica. Palabras clave: velocidad de la onda, golpe de ariete, número de Courant
iaeme, 2019
Water hammer is typically recognized by banging or thumping in water lines. While, it is still a challenge problem, even with many researches that applied for preventing or reduce this phenomenon. Although it might appear to be a smooth flow, the water inside the pipe essentially churns and tumbles as it moves through. The water have a normal sound through pipes with steady moving, even sound. The finest manner to recognize what it sounds like is to go turn the bathtub water on full blast, then go to other rooms of the house and listen. Our approach proposed a novel system implemented by FORTRAN program to mitigate the water hammer in different hydraulic systems. The program get a strong ability to find several parameters. Which is relation with the heads in pipes before and after the closing of valve. The sounds occur when valve closed abruptly or pump stoppage, the sudden rise in pressure is called (hammer blow). The noisy that pressure create as knocking. The proposed method present to our students in engineering colleges and students in agriculture colleges as a useful program for reduces this phenomenon. On the other hand, for learning several data in relation with it by add new parameters. The magnitude of pressure rise and fall depend upon: 1. The speed at which the valve is closed. 2. The length of pipeline. 3. The elastic properties of the pipe materials. 4. The elastic properties of the flowing fluid. Several factors affect water hammer like friction factor, pipe length, high of reservoir, in addition to other several parameters can be studied in this field. Cite this Article: A M Abdul Razzak, Preparing an Educational Program to Calculate the Water Hammer with Different Studies on the Phenomenon.
2005
Sudden closure of a control valve or stopping of a pump, either planned or accidental, produces excess pressure in a fluid-filled pipeline known as water hammer. Water hammer, or hydraulic transient, refers to pressure fluctuations caused by a sudden increase or decrease in flow velocity. Pressure waves in the fluid interact with axial, bending, shear a torsional stress waves in the pipe wall. The interaction between axial stress waves and fluid pressure takes place via the radial expansion and contraction of the pipe wall. It is essential to determine the magnitude and frequency of pressures and forces triggered due to these transients to estimate the stresses and vibration levels in the pipeline. This unsteady state phenomenon deals with the change between kinetic energy and pressure energy. If the pressure induced exceeds the pressure rating of a pipe given by the manufacturer, the pipe may rupture. Detrimental consequence may result unless a pressure protection device is install...
A review of water hammer theory and practice
Hydraulic transients in closed conduits have been a subject of both theoretical study and intense practical interest for more than one hundred years. While straightforward in terms of the one-dimensional nature of pipe networks, the full description of transient fluid flows pose interesting problems in fluid dynamics. For example, the response of the turbulence structure and strength to transient waves in pipes and the loss of flow axisymmetry in pipes due to hydrodynamic instabilities are currently not understood. Yet, such understanding is important for modeling energy dissipation and water quality in transient pipe flows. This paper presents an overview of both historic developments and present day research and practice in the field of hydraulic transients. In particular, the paper discusses mass and momentum equations for one-dimensional Flows, wavespeed, numerical solutions for one-dimensional problems, wall shear stress models; two-dimensional mass and momentum equations, turbulence models, numerical solutions for two-dimensional problems, boundary conditions, transient analysis software, and future practical and research needs in water hammer. The presentation emphasizes the assumptions and restrictions involved in various governing equations so as to illuminate the range of applicability as well as the limitations of these equations. Understanding the limitations of current models is essential for (i) interpreting their results, (ii) judging the reliability of the data obtained from them, (iii) minimizing misuse of water-hammer models in both research and practice, and (iv) delineating the contribution of physical processes from the contribution of numerical artifacts to the results of waterhammer models. There are 134 refrences cited in this review article.
Skalak's extended theory of water hammer
2008
Half a century ago Richard Skalak [see T.C. Skalak, A dedication in memoriam of Dr. Richard Skalak, Annual Review of Biomedical Engineering 1 (1999) 1-18] published a paper with the title ''An extension of the theory of water hammer'' [R. Skalak, An Extension of the Theory of Water Hammer, PhD Thesis, Faculty of Pure Science, Columbia University, New York, USA, 1954; R. Skalak, An extension of the theory of water hammer, Water Power 7/8 (1955/1956) 458-462/ 17-22; R. Skalak, An extension of the theory of water hammer, Transactions of the ASME 78 (1956) 105-116]
Lecture Notes for the Course in Water Wave Mechanics
2014
Technical Reports are published for timely dissemination of research results and scientific work carried out at the Department of Civil Engineering (DCE) at Aalborg University. This medium allows publication of more detailed explanations and results than typically allowed in scientific journals.
Water
Here, recent developments in the key numerical approaches to water hammer modelling are summarized and critiqued. This paper summarizes one-dimensional modelling using the finite difference method (FDM), the method of characteristics (MOC), and especially the more recent finite volume method (FVM). The discussion is briefly extended to two-dimensional modelling, as well as to computational fluid dynamics (CFD) approaches. Finite volume methods are of particular note, since they approximate the governing partial differential equations (PDEs) in a volume integral form, thus intrinsically conserving mass and momentum fluxes. Accuracy in transient modelling is particularly important in certain (typically more nuanced) applications, including fault (leakage and blockage) detection. The FVM, first advanced using Godunov’s scheme, is preferred in cases where wave celerity evolves over time (e.g., due to the release of air) or due to spatial changes (e.g., due to changes in wall thickness)....