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Showing 27 results for Subject: Water-Hydraulic Structure

Prof Javad Farhoudi,
Volume 7, Issue 4 (12-2009)


Induced total pressure by flow, including mean and fluctuating components, around a selected chute block in SAF stilling basins downstream of an ogee spillway was studied. Several pressure holes were selected on various faces of a selected chute block to get enough information regarding the total pressure field. This paper reports the results of an experimental work and measurement of mean and fluctuation pressures around chute blocks of SAF stilling basins. The observations showed that the maximum total pressure varies inversely with Froude number of incoming flow while its position of occurrence follows a quadratic polynomial relation ship. Statistical analysis also showed that the peak instantaneous pressure fluctuations could be as large as ±4.5times the RMS value.It is concluded that pressure fluctuation around the chute blocks may double the magnitude of pressure field around the chute blocks and can not be overlooked in designing such appurtenances.

F. Hajivalie, A. Yeganeh Bakhtiary,
Volume 9, Issue 1 (3-2011)

In this paper, a two-dimensional Reynolds Averaged Navier-Stokes (RANS) model is developed to simulate the shoaling, breaking and overtopping of a solitary wave over a vertical breakwater. Turbulence intensity is described by using a k turbulence closure model and the free surface configuration is tracked by Volume Of Fluid (VOF) technique. To validate the numerical model the simulation results is compared with the Xie (1981) experimental data and a very good agreement between them is observed. The results revealed that wave height and wave energy decrease considerably during the reflection from vertical wall, which illustrates a considerable energy lost during the impaction and wave overtopping process. The turbulence production during the broken wave interaction with vertical breakwater is very significant consequently the vertical breakwater undergoes sever turbulent and dynamic drag force.

E. Alamatian, M. R. Jaefarzadeh,
Volume 10, Issue 1 (3-2012)

In this article, the two-dimensional depth-averaged Saint Venant equations, including the turbulence terms, are solved in a

supercritical flow with oblique standing waves. The algorithm applies the finite volume Roe-TVD method with unstructured

triangular cells. Three depth-averaged turbulence models, including the mixing length, k-&epsilon and algebraic stress model (ASM),

are used to close the hydrodynamic equations. The supercritical flow in a channel downstream from a side-baffle in plan is then

simulated, and the numerical results are compared with the data obtained from a laboratory model. The application of different

models demonstrates that the consideration of turbulence models improves the results at the shock wave positions. The qualitative

study of the results and error analysis indicates that the ASM offers the most desirable solutions in comparison with the other

models. However, our numerical experiments show that, amongst the source term components, the negligence of turbulence terms

produces the least error in the depth estimation in comparison with the removal of the bed slope or bed friction terms.

R. Attarnejad, F. Kalateh,
Volume 10, Issue 1 (3-2012)

This paper describes a numerical model and its finite element implementation that used to compute the cavitation effects on

seismic behavior of concrete dam and reservoir systems. The system is composed of two sub-systems, namely, the reservoir and

the dam. The water is considered as bilinear compressible and inviscid and the equation of motion of fluid domain is expressed

in terms of the pressure variable alone. A bilinear state equation is used to model the pressure–density relationship of a cavitated

fluid. A standard displacement finite element formulation is used for the structure. The Structural damping of the dam material

and the radiation damping of the water and damping from foundation soil and banks have been incorporated in the analysis. The

solution of the coupled system is accomplished by solving the two sub-systems separately with the interaction effects at the damreservoir

interface enforced by a developed iterative scheme. The developed method is validated by testing it against problem for

which, there is existing solution and the effects of cavitation on dynamic response of Konya gravity dam and Morrow Point arch

dam subjected to the first 6 s of the May 1940 El-Centro, California earthquake, is considered. Obtained results show that impact

forces caused by cavitation have a small effect on the dynamic response of dam-reservoir system.

M. R. Kavianpour, E. Rajabi,
Volume 10, Issue 4 (12-2012)

The objective of this work is to perform a direct numerical simulation of turbulent channel flow where all essential scales of

motion are resolved due to variable time-stepping algorithm in various time advancement method and different discritized form

of convection term. A pseudo spectral method (Fourier series in stream-wise and span-wise directions and Chebychev polynomial

expansion in normal direction) is employed for the spatial derivatives. The time advancement is carried out by different semiimplicit

and splitting schemes. Also Alternating and Linearized forms are added to four commonly used forms of the convective

term, referred to as divergence, Convection, skew-symmetric, and rotational. Spectral method based on the primitive variable

formulation is used in Cartesian coordinates with two periodic and one non-periodic boundary condition in three dimensional

directions &Omega=[0,4&pi]×[-1,1]×[0,2&pi]. The friction Reynolds number for channel flow is set to be Re&tau=175 and the computational

grids of 128×65×128 are used in the x, y and z directions, respectively. The comparison is made between turbulent quantities

such as the turbulent statistics, wall shear velocity, standard deviation of u and total normalized energy of instantaneous velocities

in different time-discretization methods and different forms of nonlinear term. The present results show that third-order timediscretizations

forward Euler for explicit terms and backward Euler for implicit terms can minimize the computational cost of

integration by maximizing the time step, while keeping the CFL number near a threshold in time-discretization schemes. Also, the

de-aliased results of turbulence statistics do indicate that different expressions of nonlinear terms have minor discrepancy in

pseudo spectral method. The results show that the most desirable approach is a combination of variable time stepping third order

backward difference algorithm and rotational form, which provides reduced cost and further accuracy improvements.

D. Galan, M. Marchamalo, R. Martinez-Marin, J. A. Sanchez-Sobrino,
Volume 11, Issue 2 (6-2013)

New advances in geomatics and communications technologies are enabling the development of Automated Auscultation System for structure monitoring. In particular, Differential GPS (DGPS) technique allows real-time monitoring of structures with millimetre accuracy after an appropriate mathematical treatment. The results of real-time DGPS monitoring of a pilot dam over 15 months are presented and compared with the results of pendulums and angular collimation. DGPS monitoring was established to control two points at the top of the dam with reference to an external and stable station. Communications were critical, evolving from initial GPRS connections to more reliable ASDL line in the last months. Real-time DGPS positions were filtered to reach millimetric accuracy through Kalman filter. Two configurations of the filter were tested, one more adapted to predictable and uniform velocity deformations (low frequency) and another more suitable for sudden and large movements (high frequency). Root mean square errors were calculated taking pendulums as a reference. Results show that both DGPS and angular collimation allow monitoring with millimetric accuracy. In the last period, where communications with processing server were stable, a global accuracy of 1.44 and 1.86 mm was reached for real-time DGPS monitoring. RINEX post-processing yielded millimetric results, validating real-time observations. We can affirm that the DGPS system is very useful for dam auscultation and safety as it detects adequately absolute deformations, being a complement to existing methods which should be considered in new safety plans.
A. Ghare, A. Badar,
Volume 12, Issue 4 (12-2014)

The objective of field water measurement is to conserve water by improving management of its distribution and field application. A simple mobile flume to measure a discharge through small rectangular open channels in agricultural fields has been experimentally investigated. The flume consisting of a vertical cylinder inserted axially into the horizontal prismatic rectangular channel, referred as a simple cylindrical flume, has been calibrated. The flow rate in rectangular channel can be measured by constricting the flow due to presence of cylinder, resulting in critical flow conditions. Experiments have been performed on two simple cylindrical flumes of different diameters, to evaluate the hydraulic characteristics of subcritical incoming flow under free flow conditions. The results of laboratory experiments on the flume have been analysed and two different discharge prediction models have been developed. The two models developed for the prediction of discharge for simple cylindrical flumes developed for use in rectangular channel sections, are based on the energy concept and the direct regression approach, respectively. Both the proposed models have been validated using the limited experimental data available in the literature. Formation of critical depth at the throat section has also been verified. Plots have also been developed for the dimensionless column head and the corresponding Froude number of the incoming flow. The discharge prediction model giving the least error has been proposed for use in practice.
H. Khalili Shayan, J. Farhoudi, H. Hamidifar,
Volume 13, Issue 1 (3-2015)

Because of the complexity of the physical processes in the vicinity of the hydraulic structures due to the separation of the flow, traditional methods for for prediction of maximum scour depth downstream of hydraulic structures are mostly based on empirical approaches. Hence, only a few theoretical works have been reported to study this phenomenon. The present paper describes a new approach based on the momentum principles to estimate the maximum local scour depth downstream of a submerged sluice gate flowing over horizontal or adverse stilling basin. A control volume of the fluid in the equilibrium state of the scour hole was considered and based on momentum principles, some equations are derived to estimate the scour depth at equilibrium state. To verify the proposed equations, large numbers of experiments were planned and conducted under wide range of characteristic parameters such as, incoming Froude number, sediment size, tailwater depth, length and slope of the apron. It was found that the proposed equations fall in a good agreement with experimental results. It was also observed that, in the case of horizontal apron, a specific tailwater depth exists with which the local scour depth attains a minimum value. However, in the case of adverse basins when the tailwater depth takes a specific value, the maximum depth of the scour hole reaches to its maximum and then decreases to a constant value as the tailwater depth increases. This critical tailwater depth was formulated using a semi-theoretical equation.
O. Nazari, E. Jabbari, H. Sarkardeh,
Volume 13, Issue 1 (3-2015)

To dissipate energy and invert excessive discharge flow away from high dams into plunge pool, flip buckets are commonly designed and optimized by hydraulic model studies. In the present study, performance of chute flip buckets in different hydraulic and geometry conditions was investigated using experimental data of five different physical models. The collected experimental data such as Froude number, radius of flip bucket and slope of chute covered a wide range of chute flip buckets in prototype. By analyzing the data, relations for dynamic values of maximum and minimum pressures and their location along the flip bucket were extracted. Moreover, pressure distribution along the central axis of flip bucket was defined. Finally, results of the present research were compared with that of the other researches. Results of this study could be used in the design of chute flip buckets in hydraulic engineering.
A. Kaveh, R. Ghaffarian,
Volume 13, Issue 1 (3-2015)

The main aim of this paper is to find the optimum shape of arch dams subjected to multiple natural frequency constraints by using an efficient methodology. The optimization is carried out by charged system search algorithm and its enhanced version. Computing the natural frequencies by Finite Element Analysis (FEA) during the optimization process is time consuming. In order to reduce the computational burden, Back Propagation (BP) neural network is trained and utilized to predict the arch dam natural frequencies. It is demonstrated that the optimum design obtained by the Enhanced Charged System Search using the BP network is the best compared with the results of other algorithms. The numerical results show the computational advantageous of the proposed methodology.
S. Pagliara, T. Roshni, M. Palermo,
Volume 13, Issue 3 (9-2015)

Rock chutes are natural river training structures and are efficient energy dissipaters too. From the hydraulic and environmental point of view, rock chutes have become important structures in the natural river morphology. A physical study was conducted and flow properties were measured over rough bed materials of a rock chute, which was assembled at the PITLAB center of the University of Pisa, Italy. Experiments were performed for slopes varying between 0.18≤ S ≤0.38, 0.03 < dc/H < 0.54 and for ramp lengths Lr between 1.17 m ≤Lr≤3.6 m. This paper presents the energy dissipation characteristics of the two-phase flows in the presence of two different base materials. In addition, the dissipative process was also analyzed in the presence of reinforcing boulders located on the base material. The findings showed that energy dissipation rate slightly increases with the boulder concentrations for the tested slopes and materials. The experiments were conducted for different rock chute lengths in order to understand its effect on the energy dissipation. An empirical expression is developed for determining the energy dissipation characteristics over different base materials in different ramp length conditions in twophase flows. Results have been compared with the results obtained for stepped chutes and found a similar decreasing trend of dissipation rate for dc/Lr ≤0.1.
Mr. L. Yanlong, Mr. L. Shouyi, Mr. Y. Yang, Miss T. Xing,
Volume 13, Issue 4 (12-2015)

This study simulates the temperature field and temperature stress of concrete face slabs, considering the cold waves that occur during construction as well as the contact friction between the face slabs and the cushion layer. The results show that when a cold wave occurs during construction, the surface and center temperature of the face slabs continually drop with the outside air temperature, with the surface temperature drop being the largest. In addition, the surface and center of face slabs are subjected to tensile stress, with the maximum principal stress on the surface being greater than that on the center. The maximum principal stress of the surface and center occurs at approximately half of the dam height. This study also examines the surface insulation of concrete face slabs. Surface insulation can significantly improve the temperature drop range and the maximum principal stress amplitude caused by the cold wave. A stronger heat preservation results in smaller tensile stress and an increase in the amplitude of face slabs.

H. Khalili Shayan, E. Amiri-Tokaldany,
Volume 13, Issue 4 (12-2015)

Upstream blankets, drains and cutoff walls are considered as effective measures to reduce seepage, uplift pressure and exit gradient under the foundation of hydraulic structures. To investigate the effectiveness of these measures, individually or in accordance with others, a large number of experiments were carried out on a laboratory model. To extend the investigation for unlimited arrangements, the physical conditions of all experiments were simulated with a mathematical model. Having compared the data obtained from experiments with those provided from the mathematical model, a good correlation was found between the two sets of data indicating that the mathematical model could be used as a useful tool for calculating the effects of various measures on designing hydraulic structures. Based on this correlation a large number of different inclined angles of cutoff walls, lengths of upstream blankets, and various positions of drains within the mathematical model were simulated. It was found that regardless of their length, the blankets reduce seepage, uplift pressure and exit gradient. However, vertical cutoff walls are the most effective. Moreover, it was found that the best positions of a cutoff wall to reduce seepage flow and uplift force are at the downstream and upstream end, respectively. Also, having simulated the effects of drains, it was found that the maximum reduction in uplift force takes place when the drain is positioned at a distance of 1/3 times the dam width at the downstream of the upstream end. Finally, it was indicated that the maximum reduction in exit gradient occurs when a drain is placed at a distance of 2/3 times of the dam width from upstream end or at the downstream end.

Fatemeh Kazemi, Dr Saeed Reza Khodashenas, Hamed Sarkardeh,
Volume 14, Issue 1 (1-2016)

Stilling basins dissipate energy in order to form hydraulic jumps and rotational flows. Hydraulic jump and rotational current phenomenon produces pressure fluctuation at the bottom of stilling basins. In the present study, pressure fluctuations and their locations have been studied in a physical model of Nimrod Dam. Results showed that fluctuations in presence of jump in the basin are high and therefore the fluctuation factors are respectively high. Regarding available empirical equations, the thickness of slab for different hydraulic conditions were calculated and compared in 1D and 2D conditions. By analyzing collected data, it was observed that, results of 1D were underestimated in comparison by 2D calculations.

Shuai Li, Jian-Min Zhang, Wei-Lin Xu, Jian-Gang Chen, Yong Peng, Jun-Ning Li, Xiao-Long He,
Volume 14, Issue 1 (1-2016)

The cavitation erosion induced by high flow velocities is very prominent in high head and large unit discharge tunnel. Air entrainment is an effective technology to solve this problem. In this study, numerical simulation and physical model test are applied to the comparative study of air-water flows on bottom and lateral aerator in tunnel. The flow pattern, aeration cavity, air concentration and pressure distribution were obtained and there is a close agreement between the numerical and physical model values. The hydraulic characteristic and aeration effect of anti-arc section are analyzed. The results indicated that added lateral aeration facilities on 1# and 2# aerator can weaken backwater and increase the length of the bottom cavity, but it is limited to improve the air concentration and protect sidewall downstream of the ogee section. Air concentration improved on side walls downstream of anti-arc section when added lateral aeration facility on 3# aerator. The black water triangle zone disappeared and the floor and side walls well protected.

Jianwei Tu, Guang Que, Bo Tu, Jiayun Xu,
Volume 14, Issue 5 (7-2016)

Ship lift is a major navigation structure lifting and lowering ships to shorten the time across the dam. The ship chamber, the key equipment, serves as the carrier for ships. Due to its gigantic body and mass, complicated coupled vibrations occur between the chamber and ship lift structure during seismic process. With the engineering background of the ship lift at the Three Gorges dam, a three-dimensional shell finite element model is established for the ship lift, and then simplified into a three-dimensional truss finite element model through dynamic equivalent principle. And the numerical model of coupled vibration analysis is formed through static condensation, calculating the coupled vibration response between the ship lift structure and the ship chamber. The result shows that no connection and rigid connection between them are both inadvisable. Consequently, three connection devices: spring, viscous liquid damper and magneto-rheological fluid damper are applied to control coupled vibrations during artificial seismic waves. The result shows that the magneto-rheological fluid damper makes better vibration damping effect if suitable semi-active control strategy is applied, in comparison with passive control devices.

Akbar Safarzadeh, Behzad Noroozi,
Volume 15, Issue 1 (1-2017)

This paper compares the hydraulics and 3D flow features of the ordinary rectangular and trapezoidal plan view piano key weirs (PKW) using two phase RANS numerical simulations. The main aim is to investigate effects of the inlet key area and side walls angle on discharge capacity of the PKW, while keeping the developing length of the crest intact. The numerical model has been used to carry out a sensitivity analysis for geometrical parameters and hydrodynamics of the rectangular and trapezoidal weirs have been compared for wide range of water head on the weir. Results show that the trapezoidal weir has higher efficiency than the ordinary rectangular PKW. This is partly related to the inlet key flow conditions. The trapezoidal geometry increases the inlet flow area resulting in reduction of the velocity along the key axis. Consequently, flow is distributed more uniformly over the side weirs. The gradual transition of the inlet key limits the development of the recirculation zones along the side walls and it also limits the formation of the critical section along the inlet key. These phenomena result in increase of the effective weir length and thus discharge capacity increases in trapezoidal weir compared with rectangular one. Discretization of the discharge along the crest of the tested weirs clearly confirms these findings.

Jorge Garcia-Sosa, Ismael Sanchez-Pinto, Roger Gonzalez-Herrera, Eduardo Escalante-Triay,
Volume 15, Issue 1 (1-2017)

Based on the methodology of “Understanding by Design”, UbD, the course “Design of Hydraulic Structures” was developed and implemented. A series of learning experiences, with emphasis on hydraulics and hydrology, for civil engineering undergraduate students is presented that encourages the development of high technical and scientific competence, communication skills oral and in written, the ability for teamwork and the capability to learn. The experiences were designed, using the above methodology, based on learning that is desired. Once taught the course, the results obtained were compared based on the planned framework (expectations), the characterization of the student population, the course products as well as the activities, according to the students, considered relevant in the learning process.

Jiuping Xu, Qiurui Liu, Zhonghua Yang,
Volume 15, Issue 1 (1-2017)

To fully explain hydropower unit operational problems, an optimal multi-objective dynamic scheduling model is presented which seeks to improve the efficiency of reservation regulation management. To reflect the actual hydropower engineering project environment, fuzzy random uncertainty and an integrated consideration of the natural resource constraints, such as load balance, system power balance, generation limits, turbine capacity, water head, discharge capacities, reservoir storage volumes, and water spillages, were included in the model. The aim of this research was to concurrently minimize discharges and maximize economic benefit. Subsequently, a new hybrid dynamic-programming based multi-start multi-objective simulated annealing algorithm was developed to solve the hydro unit operational problem. The proposed model and intelligent algorithm were then applied to the Xiaolongmen Hydraulic and Hydropower Station in China. The computational unit commitment schedule results demonstrated the practicality and efficiency of this optimization method.

Ali Rahmani Firoozjaee, Farzad Farvizi, Ehsan Hendi,
Volume 15, Issue 2 (3-2017)

A numerical meshless method is proposed to investigate shallow water equations. Because of The numerical solution of the pure convection equations represents a very important issue in many problems, an Element Free Galerkin (EFG) method is used for solving these equations, and its implementation is described. In this method there is no need to nodal connectivity and just uses nodal data which may be the same as those used in the Finite Element Methods (FEMs) and a description of the domain boundary geometry are necessary. The essential boundary condition is enforced by the penalty method, and the Moving Least Squares (MLS) approximation is used for the interpolation scheme. The numerical efficiency of the proposed method is demonstrated by solving several benchmark examples. Sensitivity analysis on parameters of the EFG method is carried out and results are presented.

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