In the flow through the pipes, we have unstable movements when, due to the closing or opening of the valve or other hydraulic equipment, the speed of movement of the liquid changes. The change in velocity causes inertial forces to arise in the liquid which cause pressure changes in the flow. The phenomenon characterized by these pressure changes is called hydraulic water hammer.
water hammer analysis parmakian pdf 19
A hydraulic transient, also known as water hammer or hydraulic shock, is a sharp pressure surge or a wave produced when water flow is forced to stop suddenly or change direction abruptly. Power failure of pumps, sudden valve actions and the operation of automatic control systems can cause a high pressure wave to propagate in pipeline systems, including domestic water-supply networks. If the necessary precautions are not taken, the transient conditions instigating high pressures can cause failures of pipes, valves and fittings and thus collapse of the pipeline systems. Hydraulic transients may adversely affect the quality of treated water. Surge tanks, expansion tanks, pressure safety valves or accumulators can be used to ease the impact of water hammer on pipelines and their fittings [1,2,3,4,5,6,7,8,9].
The experimental studies conducted by Weston [10], Carpenter [11] and Carpenter and Barraclough [12] are reported to be the first investigations on determining a correlation between the decrease in flow velocity in a pipe and the corresponding pressure surge. Frizell [13] studied water hammer in Ogden hydroelectric development with a 9.45 km long penstock. Joukowski [14, 15] has carried out extensive theoretical and experimental studies on the basic theory of water hammer. The pipelines which were used in the studies have the lengths of 7.62 km, 305 m and 305 m with diameters of 50 mm, 101.5 mm and 152.5 mm, respectively. Joukowski derived a formula for the wave velocity, taking into consideration the elasticity of both water and the pipe walls. The general theory of water hammer was developed by Allievi [16], presenting an expression for the pressure rise at the valve and produced charts for pressure rise and fall caused by a uniform valve closure.
Since then, a number of studies have been published, refining the governing equations of water hammer [9, 17,18,19,20,21]. Their combined efforts have resulted in the classical mass and momentum equations for one-dimensional water hammer flow which is usually the basis for the numerical simulations. Karney and Ruus [22] and Elansary and Contractor [23] have investigated the influence of uniform, parabolic, equal percentage and optimum valve closure operation on hydraulic transients in pipelines. Sharp and Sharp [24] stated that two-stage valve closure arrangement can be used to reduce transient pressure in pipes. Yu et al. [25] have advised to close a valve in two steps. The first segment of the pipe could be closed in a rapid manner, while the second segment should be closed in a slow way to avoid high transient pressures. Although water hammer effect has been studied since the beginning of the twentieth century [16], due to its complexity, several features of it still remain to be investigated. In this study, three different closure schemes of a butterfly valve and two diverse pipe types were considered in order to determine the best valve closure operation to minimize hydraulic transients in pipes.
Lohrasbi and Attarnejad [8] presented a study on pressure oscillations in water networks. They developed a mathematical model for the hydraulic circuits and studied the effect of valve opening/closing on pressure oscillations. They modeled various pipe networks and observed the effects of water hammer. They concluded that slow opening/closing of valve results in less pressure surge.
The system used for the analysis is shown in Fig. 8. For current investigation, water is used as a working fluid. In the given system, a control valve has been introduced in the feed line for the calibration of flow component FLC (see Fig. 8). The system consists of a constant pressure reservoir at 26 bar. Flow components like flow-meter, pressure transmitters, electro-pneumatic valve and control valve are installed in the feed line, in addition to the Control valve IVC-101. The flow component FLC has been kept at a constant opening of 24%, which acts as a source of high pressure drop at this opening. The outlet of the feed circuit is connected to the collection tank kept at a constant pressure of 1.6 bar. Based on the inlet and outlet boundary conditions, the technical specifications of control valve IVC-104 are given in Table 1. Further, the installed characteristics of the IVC-104 are given in Table 2 and Fig. 6.
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.
Water hammer analysis is a fundamental work of pipeline systems design process for water distribution networks. The main characteristics for mine drainage system are the limited space and high cost of equipment and pipeline changing. In order to solve the protection problem of valve-closing water hammer for mine drainage system, a water hammer protection method for mine drainage system based on velocity adjustment of HCV (Hydraulic Control Valve) is proposed in this paper. The mathematic model of water hammer fluctuations is established based on the characteristic line method. Then, boundary conditions of water hammer controlling for mine drainage system are determined and its simplex model is established. The optimization adjustment strategy is solved from the mathematic model of multistage valve-closing. Taking a mine drainage system as an example, compared results between simulations and experiments show that the proposed method and the optimized valve-closing strategy are effective.
At present, the theories and methods of water hammer and its protection means become more and more mature. In summary, researches about this problem are mainly in three aspects: hydraulic transient modeling, the calculation, and protection methods of water hammer.
(1) Hydraulic Transient Modeling. For the research on hydraulic transient, from the mathematical derivation of the 18th century to the graphical analysis of the mid-20th century and to the current computer digital simulation, scholars have already made a lot of research results. The major achievements are getting the relationship between multiphase and multicomponent transient flow equations, water hammer equations, and the control equations, such as Joukowsky equation [9]. Based on the transient flow simulation theory, Colombo et al. [10] proposed an aqueducts fault detection technology, Lee et al. [11] proposed the pipe network leak and deterioration over time detection technology by the time domain reflectometry (TDR), Arbon et al. [12] proposed pipeline corrosion and blockage detection technology, Gong et al. [13] proposed a detection technology for pipe friction, wall thickness, velocity, position, and the length of the pipes, and Ferrante et al. [14] presented a leak detection method with coupling wavelet analysis and a Lagrangian model techniques. Meniconi et al. [15] presented a pipe system diagnosis method with the small amplitude sharp pressure waves.
(2) The Calculation Methods of Hydraulic Transient for Water Hammer. The calculation methods of hydraulic transient for water hammer include arithmetic method, graphic method, and numerical method.
(i) Arithmetic Method. Before the 1930s, the hydraulic transient calculation of water hammer used Allievi equations mostly [16]. Allievi equations can be called Arithmetic method which is used to solve the problems of water hammer that with simple boundary conditions and its workload is very large.
(ii) Graphic Method. Graphic method is developed in 1930s to 1960s. Bergeron, Parmakian, and so forth [17] are committed to develop this method. Boundary conditions and the process of water hammer fluctuation are expressed through coordinate graphics of and according to this method. Due to the graphics, it is simple and intuitive for the hydraulic transient calculation of water hammer. However, the accuracy is not high because this method is restricted by calculating means and assumptions.
(iii) Numerical Method. From 1960s, some numerical methods appeared that can be aided by computers, such as Characteristic (MOC) [18], Wave Characteristic Method (WCM) [19], Implicit Method [20, 21], and Finite Element Method (FEM) [22, 23]. The WCM can solve water hammer problems of complex piping systems and boundary conditions. It is the most common method because of the high accuracy and computing. The Implicit Method divides pipeline into several segments and solves equations of the entire pipeline system simultaneously in each segment. The advantage of Implicit Method can be described in a way that a longer segment is selected and the number of calculations is reduced. However, there is more time needed for calculation in large and complex pipeline network system [24]. FEM with flexibility is used in pipe network system which have complex boundary conditions. However, it has a limitation in solving hydraulic transient problems. 2ff7e9595c
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