Water Hammer Effect Research Articles

Influence of cavitation on the acoustic boundary conditions in water hammer experiments

A water hammer event is created by stopping a flow in a pipeline using a fast closing valve. The pressure is measured at three different positions upstream the valve. Cavitation occurs close to the valve and is detected by vapour pressure in the pipeline. Frequencies in the liquid part of the pipe were measured and statistically evaluated in order to analyse whether cavitation acts as a boundary condition of acoustics.Without cavitation one side of the pipe is an open end, while the other side is a closed end. In presence of cavitation the cavity should act like an open end due to the high change of acoustic impedance from liquid to gaseous phase. Therefore it is expected that the oscillating behavior is changing from an open/close to an open/open system. The measured frequencies indeed show a change towards an open/open configuration. It is shown that cavitation acts as a boundary condition in this system.

Analysis and Suppression Strategy of Transient Frequency Deviation by Soft Guide Vane Control in Hydro Turbine

The hydro-dominant characteristic is notable after the asynchronous operation in Southwest China Power Grid which brings worse transient frequency deviation caused by water hammer effect. To prevent the possible cascading failure due to the worse transient frequency deviation in the secondary frequency regulation, the soft guide vane control law is proposed to suppress the water hammer effect in the transient regulation process based on the detailed turbine-penstock model. The discrete state space expression of the turbine-penstock model is built to simulate the regulation effect in the time domain and the PSO (Particle Swarm Optimization) algorithm is applied to optimize the soft guide vane control adjustment factor considering multi-object. Finally, the emergency AGC (Automatic Generation Control) adjustment in the single machine with load transmission system is conducted to verify the effect of transient frequency deviation suppression by optimized soft guide vane control.

Experimental and numerical investigation on pressure characteristics of the dual-valve controlled fuel system for low-speed diesel engines

In order to analyze the pressure performance of a dual-valve controlled fuel system, a test bench for low-speed diesel engine fuel system was used. The experimental results showed that the system pressure fluctuation is obvious. Then theoretical analysis was performed to verify the mechanism for the apparent pressure fluctuation. The results show that the excessive pressure peak is caused by the high rising rate of fuel pressure. The difference between the fuel pressure and injection pressure is mainly correlated to the pressure loss along high-pressure fuel tube. And the pressure surge after fuel injection is due to water-hammer effect. In order to improve system structure, an AMESim model that has been validated fully was used to develop response surface prediction models of injection pressure peak, steady injection pressure and fuel injection quantity. For the determination coefficient and adjusted determination coefficient for each prediction model are more than 0.98, the calculation results from the prediction models are reliable. Based on the prediction models and Non-dominated Sorting Genetic Algorithm II, a multi-objective optimization was carried out to reduce the injection pressure peak and increase the steady injection pressure while ensure the variation of fuel injection quantity is within 10% finally. After optimization, at the cost of fuel injection quantity loss of about only 7.07%, the injection pressure peak is decreased by about 22.27% and the steady injection pressure is increased by about 33.32%.

Application of the shock response spectrum method to severity assessment of water hammer loads

Water hammer (WH) is a transient phenomenon which happens to appear in pipe flow systems as an effect of a sudden change in pipe flow conditions. Various origins can be the primary source of WH. They usually come from the liquid (e.g. operation of valves), but when the pipeline system is significantly elastic, WH can be produced by an external impact or transient vibration due to fluid structure interaction (FSI) effect. Hydraulic transients are usually undesired effects as large amplitudes of pressure waves, pipe stresses or vibration accompanying this phenomenon can be the source of pipeline system malfunction. Therefore, many efforts are taken by scientists and engineers to avoid unexpected WH events or to reduce their harmfulness. Systematic protection of pipeline systems requires a reliable method of severity estimation of WH loads. Various ways can be used for evaluation of WH strength. In general, severity of a transient depends on its amplitude, i.e. the maximum value of the liquid pressure. Another important factor is time dependence of the load signal however, a simple observation of its shape in time domain is usually not an effective technique. Instead, frequency domain analysis can be exploited. A specific kind of spectral analysis used in structural mechanics for assessment of shock loads and transients is the shock response spectrum (SRS) method. An original concept of application of this technique to WH events is proposed in this study. The method is shortly presented and its numerical approach developed by the author and applicable to WH loads are described. As an example of use the SRS computations and analysis of own WH experimental results measured at a laboratory pipeline are performed and concluded. Specific preprocessing of WH signal was applied and explained. It is evidenced in the paper that the applied SRS method gives a valuable and effective tool for determination of WH load severity. Therefore, it can also be used for comparison between alternative designs of pipeline system applied for protection from undesired WH events.

Experimental Study on the Optimal Strategy for Power Regulation of Governing System of Hydropower Station

Active power instability during the power regulation process is a problem that affects the operation security of hydropower stations and the power grid. This paper focuses on the dynamic response to power regulation of a hydro-turbine governor in the power control mode. Firstly, the mathematical model for the hydro-turbine governing system connected to the power grid is established. Then, considering the effect of water hammer and the guide vane operating speed on power oscillation and reverse power regulation, a novel control strategy based on the S-curve acceleration and deceleration control algorithm (S-curve control algorithm) is proposed to improve power regulation. Furthermore, we carried out field tests in a real hydropower station in order to compare the regulation quality of the novel control strategy based on the S-curve control algorithm with the traditional linear control strategy. Finally, the obtained results show that the proposed optimal control strategy for the hydro-turbine governor improves the stability of power regulation by effectively suppressing reverse power regulation and overshoot. This study provides a good solution for the instability of power and reverse power regulation during the regulation process of the hydro-turbine governor in the power control mode.

Investigation of the influence of dimensions and material of the pipes on the water hammer effect in microbial fuel cells wastewater treatment plants

Water hammer is a transient flow phenomenon generated in a pipeline, when there is a sudden change in velocity, due to the closing of valves. This is particularly important for plants based on complicated hydraulic circuits and piping, to avoid malfunctioning in the urban sewer network. In this study, the effect of a set of parameters: length, diameter and material of the pipe with and without surge tank on transient pressure is investigated by using the software HAMMER V8i. The results show that the maximum Transient Pressure is strongly influenced by an increase of 41.24% of the pipe diameter when the Surge Tank is not present. When the surge tank is inserted the transient pressure increases only of about 12.2%. So the surge tank can have a positive influence on the entire network. Moreover, the increase in the length will lead to a decrease in the Total Pressure of about 10% without Surge Tank and of 8.62% with Surge Tank. While the change in the roughness coefficient of the material used for the pipes will cause a decrease in the Total Pressure of about 42.6%, without Surge tank, and of 12.2% with Surge Tank.

Hydraulic axial plunger pump: gaseous and vaporous cavitation characteristics and optimization method

Gaseous and vaporous cavitation have extremely harmful effects on hydraulic axial plunger pumps, reducing flowrate and increasing flow pulsation. The collapse of vapor bubbles strongly impacts the inner wall and produces many pits. Therefore, it is very important to reduce gaseous and vaporous cavitation to improve the performance of hydraulic axial plunger pumps. In this work, a full cavitation model and a compressible model are used to simulate the two kinds of cavitation, which are validated by a series of experiments. It is found that the vapor and gaseous bubbles in the plunger chamber collapse owing to pressurization caused by the water hammer effect. The results show that a better combination of plunger chamber radius and swash plate angle can reduce the two kinds of cavitation when the theoretical flowrate is unchanged; increasing the angle of the inlet of valve plate can effectively reduce its cavitation and increase the filling mass of plunger chambers; increasing the angle of the relief groove can significantly reduce its vapor and gaseous volume fraction. The results can provide a useful reference for reducing gaseous and vaporous cavitation in the optimization and design of hydraulic axial plunger pumps.

Standoff Distance in Ultrasonic Pulsating Water Jet.

The water hammer effect is the basis of technologies which is artificially responsible for the decay of continuous jets. A recently developed technique enhances the pressure fluctuations using an acoustic chamber, leading to enhanced erosion effects for various water volume flow rates. The optimum standoff distance for an ultrasonic enhanced water jet is not appropriately estimated using an inclined trajectory. The objective of this study is to comprehend the true nature of the interaction of the standoff distance following the stair trajectory and traverse speed of the nozzle on the erosion depth. Additionally, it also critically compares the new method (staircase trajectory) that obeys the variation in frequency of the impingements for defined volume flow rates with the inclined trajectory. In this study, at constant pressure (p = 70 MPa), the role of impingement distribution with the variation of traverse speed (v = 5–35 mm/s) along the centerline of the footprint was investigated. The maximum erosion depth corresponding to each traverse speed is observed at approximately same standoff distance (65 ± 5 mm) and decreases with the increment in traverse speed (h = 1042 and 47 µm at v = 5 and 35 mm/s, respectively). The results are attributed to the variation in the number of impingements per unit length. The surface and morphology analysis of the cross-section using SEM manifested the presence of erosion characteristics (micro-cracks, cavities, voids, and upheaved surface). By varying the water cluster, different impingement densities can be achieved that are suitable for technological operations such as surface peening, material disintegration, or surface roughening.

Revisiting frequency domain analysis method for water hammer effects on pipeline systems

This paper revisits frequency domain analysis method for water hammer study in a hydraulic system. Detailed investigation of the effect of the flow parameters is conducted. Weaknesses on previous research works were pointed out. A brief presentation of the frequency response function determined from motions equations of transient water flow is firstly presented. A special emphasis was devoted to the effect of frictional flow on resonance pulsations. It was obtained that, unlike previous findings, resonance frequencies in a frictional flow are decayed from odd harmonics. This decay is more or less significant depending on the friction coefficient. The observations related to various effects are also illustrated through a set of test cases that were numerically analyzed. Additionally relative uncertainties highlighting the frictional flow effect on the accuracy of resonant pulsations detection are evaluated.

Parameter design of governor power system stabilizer to suppress ultra-low-frequency oscillations based on phase compensation

In a few of the isolated DC power-transmission systems with hydropower units (and the associated water hammer effect), inappropriate governor control parameters may weaken the system damping and stability. It has the potential to result in ultra-low-frequency oscillations (ULFO) which is below 0.1 Hz. To carry out this issue, a linearized state-space model of a multi-machine system that includes hydropower and steam turbine governor control systems is presented in this paper. The oscillation mode of ULFO about the damping characteristics of the governor control system is analyzed by the damping torque analysis method. A governor power system stabilizer (GPSS) design model predicated on phase compensation principle to heighten the damping of the governor control system to subdue ULFO is planned. To verify its effectiveness, the designed GPSS is applied to a single-machine system, a 4-machine 2-area system as well as the Yunnan power grid system of China. The simulation results demonstrate that GPSS effectively suppresses ULFO with heightened ULFO damping by the optimized settings of governor control parameters.

Simulation of the Strain Amplification in Sulci Due to Blunt Impact to the Head

Traumatic brain injury (TBI) has become a concern in sports, automobile accidents and combat operations. A better understanding of the mechanics leading to a TBI is required to cope with both the short-term life-threatening effects and long-term effects of TBIs, such as the development chronic traumatic encephalopathy (CTE). Kornguth et al. (1) proposed that an inflammatory and autoimmune process initiated by a water hammer effect at the bases of the sulci of the brain is a mechanism of TBI leading to CTE. A major objective of this study is to investigate whether the water hammer effect is present due to blunt impacts through the use of computational models. Frontal blunt impacts were simulated with 2D finite element models developed to capture the biofidelic geometry of a human head. The models utilized the Arbitrary Lagrangian Eulerian (ALE) method to model a layer of cerebrospinal fluid (CSF) as a deforming fluid allowing for CSF to move in and out of sulci. During the simulated impacts, CSF was not observed to be driven into the sulci during the transient response. However, elevated shear strain levels near the base of the sulci were exhibited. Further, increased shear strain was present when differentiation between white and gray matter was taken into account. Both of the results support clinical observations of (1).

Impact of metallic-plastic pipe configurations on transient pressure response in branched WDN

The study presented in this paper addresses the response of Metallic-Polymeric pipe configurations under water hammer events. The southern Tunisian water distribution network (WDN) is considered for the numerical studies. Hydraulic Transient in the branched WDN is initiated following an intermittent pump power stoppage. The numerical investigations were conducted using a viscoelastic model, which simulates the generated unsteady flows in closed conduits with different rheological behaviors. The method of Characteristics (MOC) with linear integration is used to solve the set of partial differential equations. A detailed analysis of the WDN response to a pump trip is first conducted. Three different Metallic-Polymeric pipe configurations were considered for the numerical study. The configurations are based on replacing the cast iron pipes located in the most sensitive regions where hydraulic transient is likely to occur with PE100 pipes. It is demonstrated that Metallic-Plastic pipe configurations have a different impact on the pressure response.

Ignition of stoichiometric hydrogen-oxygen by water hammer

The potential of water hammer events for igniting hydrogen-oxygen mixtures was examined in an experimental study. Compression waves simulating water-hammer events were created by projectile impact on a piston in a water-filled pipe terminated by a test section filled with gas. Triangular wave forms with peak pressures up to 50 MPa propagated through the piping system and compressed the gas in the test section. Experiments were carried out with both air and hydrogen-oxygen gas mixtures using high-speed video of the transparent test section, dynamic pressure and spectroscopic measurements to examine the motion of the water-gas interface and determine ignition thresholds. The impulsive acceleration of the water-gas interface and deceleration created by the compression of the gas resulted in Richtmyer-Meshkov and Rayleigh-Taylor instabilities that grew to create large distortions of the initially planar and horizontal water-gas interface. The gas layer was compressed in volume by up to a factor of 50 and the gas pressures increased to as high as 20 MPa within 2 to 4 ms. The distortion of the water surface during compression resulted in a significant increase in interfacial area and ultimately, creation of a two-phase mixture of water and compressed gas. Some ignition events were observed, but the dispersion and mixing of water with the gas almost completely suppressed the pressure rise during the ignition transient. Only by eliminating the instability of the water interface with a solid disk between the water and gas were we able to observe consistent ignition with significant pressure rises associated with the combustion.

An Experimental Study on the Performance of a Damper Fabricated by Dual Rubber Springs

In this paper several experimental investigations have been studied on the dynamic behavior of a damper using dual pre-compressed rubber springs to validate the performance of this damper in practical applications. For this aim, three specimens of the same dual polyurethane rubber spring are prepared to evaluate their mechanical behavior under fatigue and vibration tests. Hysteretic force–displacement of the quasi-static and dynamic tests after cycling loading are compared with those of the initial tests. Considering a suspended cantilever steel pipe, the dynamic properties of the system before and after installing the damper are investigated. To find the effect of damper on the natural frequency of the system, the rubber hammer impact tests are conducted in both lateral and vertical directions. Moreover, while increasing the frequency through the vibration test the acceleration and displacement amplitude of the system before and after installing the damper are compared. Furthermore, this damper is employed in a factory in the field of power generation and power piping system to dissipate the water hammer effect and provide sufficient deformation in the dual rubber spring damper.

The intermittent leakage phenomenon of incipient cracks under transient conditions in pipeline systems†

Cracks caused by water hammer are one of the most common destructive forms in water supply pipeline systems. Unlike developed cracks, incipient cracks are not likely to be found, as they do not leak under normal running conditions. However, as a potential threat, the incipient cracks may rapidly develop under severe water hammer effects. To investigate the features of incipient cracks and their effects on water supply running conditions, an experimental platform was established, equipped with an upstream tank, a long steel pipeline, a downstream valve, some incipient crack physical models and several high-accuracy pressure sensors. In experimental observation and recorded data analysis, elemental features of incipient cracks are identified and a numerical simulation model was established accordingly. Furthermore, several parameters including crack scale and location were investigated based on various cases studies. Both crack scale and location have significant effects on water hammer intensity.

Effects of instantaneous shut-in of high production gas well on fluid flow in tubing

Abstract As the classical transient flow model cannot simulate the water hammer effect of gas well, a transient flow mathematical model of multiphase flow gas well is established based on the mechanism of water hammer effect and the theory of multiphase flow. With this model, the transient flow of gas well can be simulated by segmenting the curved part of tubing and calculating numerical solution with the method of characteristic curve. The results show that the higher the opening coefficient of the valve when closed, the larger the peak value of the wellhead pressure, the more gentle the pressure fluctuation, and the less obvious the pressure mutation area will be. On the premise of not exceeding the maximum shut-in pressure of the tubing, adopting large opening coefficient can reduce the impact of the pressure wave. The higher the cross-section liquid holdup, the greater the pressure wave speed, and the shorter the propagation period will be. The larger the liquid holdup, the larger the variation range of pressure, and the greater the pressure will be. In actual production, the production parameters can be adjusted to get the appropriate liquid holdup, control the magnitude and range of fluctuation pressure, and reduce the impact of water hammer effect. When the valve closing time increases, the maximum fluctuating pressure value of the wellhead decreases, the time of pressure peak delays, and the pressure mutation area gradually disappears. The shorter the valve closing time, the faster the pressure wave propagates. Case simulation proves that the transient flow model of gas well can optimize the reasonable valve opening coefficient and valve closing time, reduce the harm of water hammer impact on the wellhead device and tubing, and ensure the integrity of the wellbore.

Table Charts for Sizing Surge Anticipating Valve in Rising Mains

Transient analysis for large rising mains is performed to protect them from worst effects of water hammer. It requires costly surge analysis software for analysing system for surge & sizing surge protection devices. If software is not available, engineers requires, selection tables or formulae pertaining to quick sizing of surge protection device for given pumping main. If size of surge protection device is known suitable cost shall be considered in budgetary estimates. Surge anticipating valve is a cost effective, compact & reliable surge protection device used in pumping mains. It is installed on delivery manifold of the pump. There are no design guidelines or selection tables available by valve manufacturers for selection of surge anticipating valves. Hence in this paper, table charts are prepared to estimate amount of surge & size of surge anticipating valve using KYPIPE TranSurge software after numerous analysis of pumping mains for various combinations of flows, diameters, elevations and lengths. In the end, software results are validated by comparing it with results obtained by experiment.

Process of pasta products forming in matrix wells with pre-compaction, plasticization and heating of dough

The existing designs of domestic and foreign matrices lack pre-compaction, plasticization and heating of dough, which leads to significant hydraulic resistance in the area where dough flow enters the forming holes of the dies and increases energy consumption, while in typical matrices the cross section of deep and empty wells is much larger than the total area of forming holes. The dough flow almost becomes uncontrollable, and this leads to water hammer effect and destruction of dies. This problem can be solved by installing special inserts in in the matrix wells (depth of wells is 50-120 mm). The paper shows a new direction in design of matrices for production of pasta, in particular, it is proposed to install spiral inserts in the wells of matrix, manufactured in the form of Venturi tubes. Rheological basis of dough flow in the cylindrical channels of the insert are considered, mathematical models for determination of the dough volume flow rate and dough flow rate are constructed. It is theoretically established that the volume flow rate of the dough Q0 and its flow rate depend on the length of the cylindrical channel and the viscosity of dough. The results of experimental researches are presented. It is empirically established that the inserts located in the wells of the matrix pre-compact dough, plasticize and heat it, the productivity of the press machine MIT-2 due to increasing the speed of extrusion is increased averagely by 25-26 % with significant improvement in quality of the formed semi-finished products and reduction of energy consumption.

Improved accuracy optimal tuning method for hydropower units’ governor controller

This paper aims to improve the model of the hydro-turbine system under the effect of water-hammer for frequency-domain studies. It brings out a novel way to overcome the accuracy limitation linked to the simple first and second-order approximations of the gate-turbine transfer function. The proposed study is based on the detailed model of the hydraulic system considering the effects of water compressibility and pipe elasticity. The improved system is controlled using particle-swarm optimization algorithm, which is shown to be very efficient in controlling the overshoot and stability of the system connected to a single machine single load test system. Step response and load disturbance are simulated. Results from our example prove that covering accurately a frequency range from 0 to over 30Hz is easily made when using this method for frequency-domain simulations of hydropower plant load-frequency control.

Transient Study of Flow and Cavitation Inside a Bileaflet Mechanical Heart Valve

A mechanical heart valve (MHV) is an effective device to cure heart disease, which has the advantage of long life and high reliability. Due to the hemodynamic characteristics of blood, mechanical heart valves can lead to potential complications such as hemolysis, which have damage to the blood elements and thrombosis. In this paper, flowing features of the blood in the valve are analyzed and the cavitation mechanism in bileaflet mechanical heart valve (BMHV) is studied. Results show that the water hammer effect and the high-speed leakage flow effect are the primary causes of the cavitation in the valve. Compared with the high-speed leakage flow effect, the water hammer has a greater effect on the cavitation strength. The valve goes through four kinds of working condition within one heart beating period, including, fully opening stage, closing stage and fully closing stage. These four stages, respectively, make up 8.5%, 16.1%, 4.7% and 70.7% of the total period. The cavitation occurs on the fully closing stage. When the valve is in closing stage, the high pressure downstream of the valve lasts for about 20 ms and the high-speed leakage flow lasts for about 200 ms. This study systematically analyzes the causes of cavitation emerged in the process of periodic motion, which proposes the method for characterizing the intensity of the cavitation, and can be referred to for the cavitation suppression of the BHMV and similar valves.