Water Hammer Effect Research Articles

Calculation of the Natural Frequencies of a Fluid-Filled Pipe System With the Coupled Codes dyvro/rohr2: Implementation of an Alternative Coupling Concept

Abstract The vibration of a pipe system can be caused by internal excitation, e.g., as a result of pump-induced pressure pulsations or external excitation like earthquake. For the investigation of these phenomena, the knowledge about the natural frequencies of the pipe system is essential. In this context, it is important to consider that the natural frequencies of the coupled system of fluid and structure commonly differ from the natural frequencies of the pure fluid system and of the structural pipe model in which the fluid is only taken into account as added mass. To obtain realistic natural frequencies of a pipe system filled with a fluid, the one-dimensional fluid code dyvro was coupled with the code rohr2stoss that deals with dynamic analysis of complex piping and steel structures. Two code coupling concepts were realized, the integral concept, which is also commonly used in coupling commercial pipe system software, and the alternative local coupling concept, with which the longitudinal deformation of the pipe segments can be captured. Both concepts consider a two-way fluid–structure interaction (FSI). For the integral concept, a verification was performed by comparison with an analytical solution for a simple case with a fluid column connected to a spring–mass system. Additionally, both coupling concepts were validated by comparison with experimental data from literature that revealed strong FSI during a water hammer event. The frequency content of the measured pressure fluctuations could be captured by both coupling concepts.

Multi-scale oscillation characteristics and stability analysis of pumped-storage unit under primary frequency regulation condition with low water head grid-connected

This paper aims to study the multi-scale oscillation characteristics and stability of pumped storage unit(PSU) under primary frequency regulation(PFR) condition with low water head grid-connected. Firstly, a novel nonlinear mathematical model of pumped storage unit governing system(PSUGS) considering the nonlinear characteristics of diversion tunnel is established, and the nonlinear state equations under power control mode is deduced. On this basis, the bifurcation characteristics and dynamic response process of PSUGS system with coupled first-order, third-order and fifth-order synchronous generator are studied respectively, and the effects of different order synchronous generator on the nonlinear PSUGS system are compared. In addition, the transient characteristics of the nonlinear PSUGS system considering the fifth order synchronous generator under different water heads are studied. Finally, the sensitivity of the regulation system parameters of PSU under PFR with low water head is analyzed, and the effects of hydraulic, mechanical and electrical factors on the multi-scale oscillation characteristics and stability of the nonlinear PSUGS system are revealed. The results show that the stability of PSU considering the first-order synchronous generator is less than that considering the third-order and fifth-order synchronous generator. The stability of PSU considering the third-order synchronous generator is close to that considering the fifth-order synchronous generator. In the operation of PSU, the lower the water head, the smaller the stability of the system. Under PFR condition, the nonlinear PSUGS system meets the supercritical Hopf bifurcation. During PFR oscillation of the unit, the high-frequency wavelet is excited by the generator excitation system and is sensitive to the q-axis parameters of the generator. The low-frequency wavelet is mainly excited by the power grid and mapped with the water hammer effect in the dynamic process. The research results of this paper provide a theoretical basis for the stability analysis and optimal regulation of PSU under PFR condition with low water head.

Numerical Modeling of the Hydrodynamic Performance of Slanted Axial-Flow Urban Drainage Pumps at Shut-Off Condition

Increasing extreme rainfall events caused by global climate change have had a significant impact on urban drainage systems. As a critical component of a pumping station, a large-scale slanted axial-flow pump (SAFP) featuring high specific speed plays a critical role in mitigating urban flooding and waterlogging. In this study, to reveal the transient characteristics of a SAFP at shut-off conditions, a computational fluid dynamics (CFD) based approach with dynamic mesh was proposed. Multiple shut-off conditions with various shut-down speeds of the sluice gate (SG) were modeled. Our analysis demonstrated that both the shut-off conditions and the slanted structure have conspicuous impacts on the hydrodynamic performance of a SAFP. Reducing the shut-down speed leads to a greater reverse flow rate and higher runner speed. The water hammer effect was simulated with different shut-down speeds, increasing the water head by 5.07–10.42 m, the axial force by 163.46–297.06 kN∙m, and the axial moment by 116.05–224.01 kN∙m. Compared with the axial direction, moments in the radial directions were found with more obvious oscillation as a result of stronger rotor–stator interaction. Due to the gravitational effect of the slanted structure, the fluctuation of the runner in vertical direction presented an off-axis characteristic compared with the horizontal one. As the SG speed increased, pressure fluctuations gradually decreased at various locations across the SAFP.

Establishment and Solution of Four Variable Water Hammer Mathematical Model for Conveying Pipe

Transient flow in pipe is a much debated topic in the field of hydrodynamics. The water hammer effect caused by instantaneous valve closing is an important branch of transient flow. At present, the fluid density is regarded as a constant in the study of the water hammer effect in pipe. When there is gas in the pipe, the variation range of density is large, and the pressure-wave velocity should also change continuously along the pipe. This study considers the interaction between pipeline fluid motion and water hammer wave propagation based on the essence of water hammer, with the pressure, velocity, density and overflow area set as variables. A new set of water hammer calculation equations was deduced and solved numerically. The effects of different valve closing time, flow rate and gas content on pressure distribution and the water hammer effect were studied. It was found that with the increase in valve closing time, the maximum fluctuating pressure at the pipe end decreased, and the time of peak value also lagged behind. When the valve closing time increased from 5 s to 25 s, the difference in water hammer pressure was 0.72 MPa, and the difference in velocity fluctuation amplitude was 0.076 m/s. The findings confirm: the greater the flow, the greater the pressure change at the pipe end; the faster the speed change, the more obvious the water hammer effect. High-volume flows were greatly disturbed by instantaneous obstacles such as valve closing. With the increase of time, the pressure fluctuation gradually attenuated along the pipe length. The place with the greatest water hammer effect was near the valve. Under the coupling effect of time and tube length, the shorter the time and the shorter the tube length, the more obvious the pressure fluctuation. Findings also confirm: the larger the gas content, the smaller the fluctuation peak of pipe end pressure; the longer the water hammer cycle, the smaller the pressure-wave velocity. The actual pressure fluctuation value was obviously lower than that without gas, and the size of the pressure wave mainly depended on the gas content. When the gas content increased from 1% to 9%, the difference of water hammer pressure was 0.41 MPa.

Numerical Investigation of Condensation-Induced Water Hammer Effects in Horizontal and Vertical Cold Reheat Pipes

Numerical Investigation of Condensation-Induced Water Hammer Effects in Horizontal and Vertical Cold Reheat Pipes

Water Hammer In Irrigation Systems

Irrigation system design includes pump sizing and selection, valve sizing and selection, and pipe sizing as well as the proper selection and placement of many other components. Good design involves selecting and sizing components to perform their intended tasks within the constraints of the system, to ensure an efficient, cost effective, and durable irrigation system. Cost effectiveness will result when oversizing is avoided. Undersizing of components will cut initial costs but often results in poor irrigation distribution uniformity or the complete or partial failure of the system through ruptured pipes, damaged valves, or pump damage. Like any other moving fluid, flowing water has momentum. When subjected to a sudden change in flow, shock waves propagate through the system. This occurrence is referred to as "water hammer." Flow changes can occur due to operation of valves, starting and stopping of pumps, or directional changes caused by pipe fittings. The intensity of water hammer effects will depend upon the rate of change in the velocity or momentum. This publication discusses the causes of water hammer and the importance of proper system design and management to ensure a cost effective, long-lasting irrigation system.

Water Hammer and Harmonic Excitation Response With Fluid-Structure Interaction in Elbow Piping

Abstract This study focuses on the numerical analysis of a piping structure subjected to the water-hammer event caused by a rapid valve closure that is combined with external harmonic loading representing an idealized machine excitation. The fluid–structure interaction procedure applied to solutions involves the method of characteristic for the fluid equations with the finite element method for pipe structures, which are modeled as beams. Junction coupling at the pipe elbow governs the two-way coupled fluid–structure interaction, and both the friction and Poisson couplings are incorporated as well. There is an application on a piping structure that consists of a valve, tank, and elbow that are defined as boundary conditions. The solved result quantities include pressure and bending stress responses as well as dynamic displacement modes of the piping structure. Comparisons of the results show that water hammer loading combined with the mechanical excitation load induces significantly increased displacements and higher stress peaks when frequencies of the harmonic load and the acoustic natural mode of the piping system coincide. Additionally, the resulting mode of lateral structural vibration of the piping member closely resembles an analytically solved eigenmode of the beam. The conclusion is that dynamically changing flows due to a water hammer event can solely excite natural frequencies of the piping structure causing resonance in the system.

Utilizing the water hammer effect to enhance the mechanical properties of AISI 304 welded joints

Utilizing the water hammer effect to enhance the mechanical properties of AISI 304 welded joints

Simulation Research on System Characteristics of Valve Opening Curve of Bidirectional Water Transfer System

Due to long pipelines, complex hydraulic conditions, and high flow rate, Bidirectional Water Transfer System of ship is prone to producing Water Hammer Effect when the valve opens and closes, which has a great impact on the pipeline system. In this paper, Flowmaster software is used to simulate the Bidirectional Water Transfer System to study the system characteristics under different valve opening curves. The simulation results show that when the valve opens and closes, Bidirectional Water Transfer System will have a large pressure mutation. But the pressure changes of the stepped and the stepped curve opening curves are smaller and smoother than that of the linear opening curve. But the stepped and the stepped curve opening curves can’t eliminate the pressure and flow rate mutation when the valve opens and closes; In addition, the stepped and the stepped curve opening curves can effectively improve the phenomenon of water flowing out of the reservior, and effectively avoid the phenomenon of gas flowing into the reservior.

Water Hammer Control Using Additional Branched HDPE Pipe

In pressurised pipeline systems, various water hammer events commonly occur. This phenomenon can cause extensive damage or even lead to a failure of the pumping system. The aim of this work is to experimentally re-examine the possibility of using an additional polymeric pipe, installed at the downstream end of the main pipeline, to control water hammer. A previous study on this topic investigated additional polymeric pipes connected to the hydraulic system with a short joint section of the same diameter as the main pipeline. In the current research, a different method of including an additional pipe was considered which involved connecting it with a pipe of a smaller diameter than the main pipeline. Three additional HDPE pipes, with different volumes, were investigated. The performance of the devices was studied for hydraulic transients induced by both rapid and slow, manual valve closures. Experimental results show that the additional polymeric pipe can provide significant pressure surge damping during rapid water hammer events. As the valve closing time lengthens, the influence of the additional pipe on the maximum pressure increase is reduced. The additional HDPE pipe does not provide notable protection against hydraulic transients induced by slow valve closure in terms of reducing the first pressure peak. No relationship between the volume of the additional pipe and the damping properties was noticed. The observed pressure oscillations were used to evaluate a one-dimensional numerical model, in which an additional pipe is described as a lumped parameter of the system. The viscoelastic properties of the device were included using the one element Kelvin–Voigt model. Transient flow equations were solved with the implicit method of characteristics. Calculation results demonstrate that this approach allows one to reasonably reproduce unsteady flow oscillations registered during experiments in terms of the maximum pressure increase and pressure wave oscillation period.

Mitigation of membrane fouling by whey protein via water hammer

Fouling is a major concern in membrane-based separation processes across industries. In this study, a transient back-pressure (water hammer) was applied to mitigate fouling in ultrafiltration of whey proteins. The water-hammer effect was generated by an instantaneous flow disruption on the retentate side of the membrane at definite intervals. Unsteady state shear and inertial lift at the membrane surface arising from the backpressure generated by the water hammer was believed to mitigate membrane fouling. The efficacy of the technique was evaluated by monitoring the permeate flux as well as by Fourier-transform infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) analyses. The experimental results indicated that water hammer was effective to reduce fouling in ultrafiltration of whey protein. Depending on the operating conditions, up to 84% flux enhancement could be achieved. Water hammer became less effective at high transmembrane pressures (TMP) and high feed concentrations where fouling was more severe.

Pengujian Water Hammer Pada Berbagai Berbagai Tekanan Hidrostatis

Fluids are an important aspect of everyday life. A fluid is a substance that can flow. In the pipeline, the problem that often occurs is the occurrence of fluctuations in water pressure due to the sudden closure of the water flow. The purpose of this research is to study the effect of water hammer on pressure fluctuations at various heights, and to determine the phenomenon of water hammer on flow in pipes at various water surface elevations. The research method was carried out by testing the water hammer at hydrostatic pressure with a water level of 2.40 m, 2.60 m, and 2.80 m. The test is carried out in conditions just after the valve is closed. From the results obtained for the height of h 2.40 m, 2.60 m and 2.80 m have a discharge of 0.000543 m3/s, 0.000558 m3/s and 0.000568 m3/s. pressure fluctuations in the pipe for a height of 2.40 (m), with a duration of fluctuation of 12.48 (s), for a height of 2.60, (m) with a duration of fluctuation of 14.37 (s), and at a height of 2.80 (m) fluctuated by 17.56 (s). The higher the water level, the higher the fluctuations produced. The occurrence of altitude fluctuations is caused by the closing of the valve at the end of the pipe so that the water increases and after experiencing an increase there is a decrease in height until it is constant

Damping of inter-area oscillations by combining control strategies in hydropower plants

This paper examines how the damping capability can be improved if inter-area oscillations occur by combining control strategies in hydropower plants. First, the control challenges of hydropower plants, such as the water hammer effect, are discussed. In a single-machine infinite bus system (SMIBS), the use of a Power System Stabilizer (PSS) in the generator excitation and in the governor control path as well as the combination of both strategies are examined for their effectiveness in terms of their damping capability. In addition, these results are compared with an optimal state space controller with an observer as a damping element. The Heffron-Phillips model is the design model for the PSS as well as for the model-based controller. The verification of the damping capability through the PSS variants is evaluated by using a three-machine model in the time domain and by using modal analysis.

An equivalent method of jet impact loading from collapsing near-wall acoustic bubbles: A preliminary study

Cavitation damage is a micro, high-speed, multi-phase complex phenomenon caused by the near-wall bubble group collapse. The current numerical simulation method of cavitation mainly focuses on the collapse impact of a single cavitation bubble. The large-scale simulation of the cavitation bubble group collapse is difficult to perform and has not been studied, to the best of our knowledge. In this study, the equivalent model of impact loading of acoustic bubble collapse micro-jets is proposed to study the cavitation erosion damage of materials. Based on the theory of the micro-jet and the water hammer effect of the liquid–solid impact, an equivalent model of impact loading of a single acoustic bubble collapse micro-jet is established under the principle of deformation equivalence. Since the acoustic bubbles can be considered uniformly distributed in a small enough area, an equivalent model of impact loading of multiple acoustic bubble collapse micro-jets in a micro-segment can be derived based on the equivalent results of impact loading of a single acoustic bubble collapse micro-jet. In fact, the equivalent methods of cavitation damage loading for single and multiple near-wall acoustic bubble collapse micro-jets are formed. The verification results show the law of cavitation deformation of concrete using equivalent loading is consistent with that of a micro-jet simulation, and the average relative errors and the mean square errors are insignificant. The equivalent method of impact loading proposed in this paper has high accuracy and can greatly improve the calculation efficiency, which provides technical support for numerical simulation of concrete cavitation.

Model and protected design of water piping system to minimize the water hammer effect

The effect of the water hammer is investigated to predict the water hammer effect in a wastewater pipeline and to develop the piping system design to overcome the predicted effect. The piping system is sensitive to any effects of the water hammer phenomenon. The sudden change in pressure within pipes or conduits used to transport liquid under pressure may result in serious damage. A modified numerical approach is developed to predict the water hammer effect. The system under study was modified to handle and reduce the effect of water hammer.By calculating the water hammer’s effect, the safe piping system design can be developed. A model was developed to predict the effect of water hammer and the expected pressure drop/increase across the piping system. The pipe properties and measured pressure are the model operating parameters. The maximum and minimum pressure envelopes across the piping system were calculated. By simulating the power failure and/or pump shut down, the model showed a good prediction for the effect of piping system design variations. The optimum design for the piping system was developed and presented.

RETRACTED: Analytical and CFD analysis investigation of fluid-structure interaction during water hammer for straight pipe line

The aim of this study is to show the influence of the effect of water hammer at the level junctions and valves on the values of the pressure and velocity for the fluid and the axial velocity and stress for the piping on the exact solution of the FSI four-equation model of two filling pipes system by using two methods, the first is the analytical method and the second is the computational fluid dynamics (CFD) method. The application of the conservation laws of the mass, momentum, and energy for a flow transient in driving, leads us to a system of differential equations to partial derivatives of the hyperbolic type. This equation system takes into account counts the two fluid-pipe interaction, the pipe velocity, as well as mechanical vibrations at the junctions or valves. The exact solution of the FSI four-equation model by a Tijsseling model (Tijsseling, 2009) [1]. The resolution of this system of equations is done by the method of characteristics coupled with finite differences. The proposed model was tested by a comparison with the results of Ahmadi et al. (Ahmad and Ali, 2008) [2] validated with those of Heinsbroek.

Study on the Strategy of Improving the Primary Frequency Regulation Capability by Adaptive Parameters of Turbine Governor

Many studies have shown the inverse regulation characteristics of water hammer effect inherent in the hydropower system and the unreasonable parameter configuration of the governor result in the generation of the ultra-low frequency oscillation. The main research work of this paper is above two points. Based on the detailed analysis of the influence of each parameter of the speed regulating system on the frequency characteristics of primary frequency regulation, combining with the improved particle swarm optimization algorithm, a self-adaptive parameter configuration technology on PID governor of hydraulic turbine regulation system is presented, the PID parameters can be adjusted continuously according to the rotation speed deviation. And the simulation analysis is carried out. The effectiveness of the adaptive PID parameter method to improve the primary frequency regulation ability is verified.

Hydraulic Transients in Viscoelastic Pipeline System with Sudden Cross-Section Changes

It is well known that the water hammer phenomenon can lead to pipeline system failures. For this reason, there is an increased need for simulation of hydraulic transients. High-density polyethylene (HDPE) pipes are commonly used in various pressurised pipeline systems. Most studies have only focused on water hammer events in a single pipe. However, typical fluid distribution networks are composed of serially connected pipes with various inner diameters. The present paper aims to investigate the influence of sudden cross-section changes in an HDPE pipeline system on pressure oscillations during the water hammer phenomenon. Numerical and experimental studies have been conducted. In order to include the viscoelastic behaviour of the HDPE pipe wall, the generalised Kelvin–Voigt model was introduced into the continuity equation. Transient equations were numerically solved using the explicit MacCormack method. A numerical model that involves assigning two values of flow velocity to the connection node was used. The aim of the conducted experiments was to record pressure changes downstream of the pipeline system during valve-induced water hammer. In order to validate the numerical model, the simulation results were compared with experimental data. A satisfactory compliance between the results of the numerical calculations and laboratory data was obtained.

Elevated tanks effect on transient pressures: case study

Abstract Elevated tanks are an integral part of the water supply networks. This paper highlights the effect of elevated tanks' location and size on the transient pressures resulting from the sudden failure of pumps. A comparison between the impact of elevated tanks and air vessels on the water hammer was also performed. The Bentley HAMMER model was first validated then applied to analyze the unsteady flow within an actual distribution network. The results display that the elevated tanks have a considerable effect on the surge pressures, where they improve the extreme pressures effectively at and around them, but they cannot fully protect the system from the water hammer risks, as there are still relatively large negative pressures at some distant junctions. Besides, as the tank capacity increases, the surge pressures increase slightly. In our case study, the best location of the elevated tank is at the network extremity and then at the pumping stations, since the minimum pressures improve by 67 and 54%, respectively. Although the present case study may differ from other supply systems, the obtained results can provide an indication of the elevated tanks' role in alleviating undesirable water hammer effects.

Experimental research on the mechanisms of condensation induced water hammer in a natural circulation system

Natural circulation systems (NCSs) are extensively applied in nuclear power plants because of their simplicity and inherent safety features. For some passive natural circulation systems in floating nuclear power plants (FNPPs), the ocean is commonly used as the heat sink. Condensation induced water hammer (CIWH) events may appear as the steam directly contacts the subcooled seawater, which seriously threatens the safe operation and integrity of the NCSs. Nevertheless, the research on the formation mechanisms of CIWH is insufficient, especially in NCSs. In this paper, the characteristics of flow rate and fluid temperature are emphatically analyzed. Then the formation types of CIWH are identified by visualization method. The experimental results reveal that due to the different size and formation periods of steam slugs, the flow rate presents continuous and irregular oscillation. The fluid in the horizontal hot pipe section near the water tank is always subcooled due to the reverse flow phenomenon. Moreover, the transition from stratified flow to slug flow can cause CIWH and enhance flow instability. Three types of formation mechanisms of CIWH, including the Kelvin-Helmholtz instability, the interaction of solitary wave and interface wave, and the pressure wave induced by CIWH, are obtained by identifying 67 CIWH events.