فهرست مطالب manoochehr fathi moghadam

Rivers are known as the main sources of surface water in the world, which experience seasonal fluctuations in water level. These resources have severe damage to human societies and nature in flood conditions and have irreparable consequences in the drought seasons. Optimal utilization of these resources with maintaining the environmental conditions of the waterway and minimizing flood damage is considered one of the river engineering goals. Since the conventional methods of river management are imposed serious environmental threats on waterways and wetlands, consideration to these water resources requires attention to issues related to plant ecosystems, solving challenges of coastal bed erosion and predict the condition and management of the river in the future (Callow, 2012; Dawson and Haslam, 1983; Fan et al., 2013; Rose et al., 2010; Rowinski et al., 2018). One of the strategies that cause loss of flow energy in the river improves the hydrological system and river ecosystem is the presence of vegetation in the river banks and floodplains. Native vegetation in floodplains and coastal forests plays an important role in conserving waterway ecosystems, flood management, coastal protection in urban lands and agriculture adjacent to the river (Fathi-Moghadam, 1996). Vegetation will also control the width of the river and increase the stability of the shores by absorbing and settling suspended sediments in river banks. The plant species along rivers and waterways are composed of various vegetative components, mainly affected by the environmental conditions of their habitat, including the distance from the waterway bed, hydrological characteristics of the river, climatic and soil conditions. Obviously, the effect of each plant species in the ecosystem cycle varies and for each section of the river, a specific combination of plants will create optimal conditions.

The analysis of transient flows in closed ducts has always been one of the most important and favorite topics of hydraulic engineers. On the other hand, with operation of water supply facilities during the time, water leakage may occur anywhere in the transmission pipeline system. Haghighi and Ramos (2012) performed leak detection in pipelines using inverse transient analysis and CFO optimization method. Mohammadi and Fathi-moghadam (2013) analyzed the fast transient flow in pipelines by the unsteady friction model. Akbari et al. (2021) investigated the detection of leaks in polyethylene transmission pipelines using pressure wave reflection of transient flow. Therefore, using laboratory modeling, fast unsteady flow in leaking pipelines was investigated, and then, a computer model was coded by Visual Basic programming language, with the ability to simulate transient flow in pipelines in presence of leakage. Then the parameters of temporal and spatial acceleration coefficients kut and kux and discharge coefficient of leak orifice cd were calculated.

In this research, a 47m long pipe that made of polyethylene with 10bar nominal pressure and diameter of 63mm was used in experiments. The transient flow was generated in it by very fast closure of the end valve. A computer numerical program was developed to simulate the hydraulic conditions in pipeline. The coded model analyzer motor analyzes the basic unsteady flow equations in pressurized ducts, and the inverse analyzer is an optimization algorithm using a defined goal function to find the best fit of the recorded pressure waves and those simulated with the least error. Also, the boundary conditions for simulating the leak in the pipeline were included in the numerical model.

The values of kut and kux coefficients related to the wave simulations was calculated. The values of kut for leakage and non-leakage state were approximately the same, and the coefficient of kux for leak state would be less than non-leakge state. In the case of leaks with different diameters, the coefficient of kut were generally the same as in the case of non-leakage. However, the values of kux coefficients for leakage with a diameter of 4 mm were greater than those for leakage with a diameter of 10 mm, and both of these values were less than non-leaking. The reason is that as the diameter of the leak increases, the damping rate of the pressure waves increases, therefore the value of the kux coefficient decreases.The change in the leak location had almost no effect on the values of kut and kux. The coefficient of kux in the presence of leak, either at a distance of 27 m or 39 m, were less than its values in non-leak state, and both values were also approximately equal to each other. Leak orifice with a larger diameter (10 mm) had a higher discharge coefficient than leak with a smaller diameter (4 mm), due to their lower resistance and lower energy dissipation against the increase in pressure produce in the system by the transient pressure wave. The performance of the two-coefficient unsteady friction model was evaluated by statistical indexes. Also, the numerically simulated waves and the laboratory samples was compared to each other. The two-coefficient unsteady friction model had a good ability to simulate a transient pressure wave in presence of a leak.

The values of kut for leak and no-leak state were almost constant and the values of kux for leak state was less than the kux for the no-leak state. Changes in leak location had almost no effect on the values of kut and kux. Selecting a steady or unsteady type of friction model to simulate the transient flow in the presence of leakage had almost no effect on the orifice discharge coefficient. Two coefficient unsteady friction model had a good ability to simulate the pressure wave of transient flow in the presence of leakage.

The analysis of transient flow plays a critical role in designing pipe systems and pipe networks. Controlling and collecting the pressure wave signals at proper spots in the pipeline can provide much information about the system. Many researchers have studied transient flow and the loss caused by unsteady flow (Brunone et al, 1991; Pezzinga, 1999; Vitkovsky et al., 2000).
Compared with steel pipes, the use of polymer pipes such as polyethylene (PE) and PVC in pipelines and pipe networks has attracted much attention due to their superior properties. Researches have been conducted on the dynamic behaviour of these pipes on transient flow. Brunone et al. (1995) explained that pressure wave damping in a polyethylene pipeline is caused by unsteady friction loss; however, the research showed that there is a large difference between the numerical and the experimental results, and this is due to the viscoelastic effects of polymer pipe walls, which were neglected in this study. Soares et al. (2008) examined the viscoelastic behaviour of PVC pipes on transient flow. The creep function of these pipes was calculated by inverse solution of the transient flow. The results showed that the damping, scattering, and shape of the transient pressure waves are fully described by taking into account the viscoelastic behaviour in the developed numerical model. Carriço et al. (2016) studied the uncertainties of the transient flow numerical model in polyethylene pipes, indicating that unsteady friction loss and viscoelasticity of polyethylene pipe walls have parallel effects on transient signals and the effects cannot be simultaneously distinguished.
Most studies have been so far conducted on the transient flow in a simple pipeline made up of steel and concrete. Since few research has been done on transient flow in more complex systems and plastic pipes, the present paper investigates the numerical and experimental model of transient flow and its properties in polyethylene pipe networks in time domain. In this study, by collecting transient signals of the pipe network, unknown parameters are calibrated and extracted by inverse analysis of the transient flow for different discharges. The pressure signal properties in polymer pipes are also compared with discharge variations.

The complex interactions between streameise flow and curvature- induced secondary flow in bends, bed morphology cause erosion near the outer bank, and deposition near the inner bank, that it can endanger the outer bank’s stability and also reduce the navigable width of the rivers. There are several techniques to protect the outer bank, reduce adverse impacts and control bed erosion in bends. Methods used in most parts of the world include submerged groynes, spur dikes, and bandal-like structures. But, meny these Methods have the disadvantage of being fixed constructions on the bed river that caused a threat for navigation. This paper describes a new way that consists in changes the bed morphology with provoking changes in the flow pattern. Dugue, et al. (2011, 2012) studied morph dynamic bends rivers with the Air-bubble screen method. Their results reveal that the air bubble screen is able to modify the flow pattern by shifting the maximum scouring from the outer bank towards the center of the flume and does not endanger its stability anymore. Dugue et al, 2013 studied scour reduction at a 193° bend by an air-bubble screen method. Velocity pattern at 70° bend showed that the bubble-induced flow pattern overcame the secondary flow induced by the outer bank while decreasing the morphology slope. It also showed 50 percent reduction in the maximum scour depth. Shukry (1949) is one of the first researchers in the study of erosion of the outer bank of rivers in a canal with a 180- degree bend with various proportions of the rivers radius to its width. There have been very few investigations about air bubble screen in 90 bend, therefor  in this study the effect of the air bubble screen on flow pattern and Secondary flow strength  and bed shear stress in 90 degree bend under Froude numbers 0.45 is examine.

Measuring flow discharge in rivers and open channels has always been one of the most important concerns of water sciences experts. The most common flow measurement method in open channels is velocity- area approach. An approach recently considered as a non-contact option for measuring flow is the use of surface flow image velocimetry methods. Recently, the standard PIV method has been used to measure the velocity at larger scales and on the flow surface, which is referred to as the LSPIV (Bieri et al., 2009).The most common way of converting the surface velocity to the depth-averaged velocity is to use a coefficient called the Velocity Index (VI) which is in fact the ratio of the depth-averaged velocity to the surface velocity. In the literature, the value of the Velocity Index for river flows and laboratory flumes, which were mainly studied for subcritical conditions, is believed to be equal to 0.85, which seems to be an accepted value for this index among the hydraulics communities.In this research, an image velocimetry technique was used to study the flow characteristics, determine the Velocity Index and investigate the surface flow pattern. The instantaneous surface velocity field was measured using the LSPIV method and then a two-dimensional time-averaged velocity map was obtained for different experiments providing the possibility of comparing the flow pattern in different scenarios. Furthermore, by means of spatial averaging of the time-averaged velocity map, the double averaged surface velocity  was obtained using which and the cross-sectional mean velocity the Velocity Index was calculated. Therefore, the effect of channel slope and relative submergence on the Velocity Index was investigated and relationships were proposed to estimate the VI in steep slopes.

Hydraulic jumping is a complex three-dimensional phenomenon which is frequently observed in open channel flow such as rivers. The hydraulic resistance of vegetation plays a major role in the hydrodynamics of rivers with extensive natural floodplains. Vegetation penetrates the flow field and creates resistant force and, consequently, energy dissipation. In this study, the effect of vegetation density and height on flow in a hydraulic jump and parameters related to two phase Air-water flow are examined using cylindrical elements made of galvanized iron with a homogeneous diameter of 7 mm as vegetation. Thus, neither the effects of plant diversity nor flexibility have been considered. For this purpose, four forms of rough bed were used in two modes of staggered and collocated grid roughness with two heights of 1.5 and 3 cm, and the results were compared with data on smooth bed as a reference. Experiments were conducted in a horizontal rectangular flume with a width of 30 cm, in the range of upstream Froude numbers between 1.5 Fr1 5.5. Air-water flow measurements were conducted with a dual-tip conductivity probe, which was designed, developed and calibrated in this research. The results of this study showed that the presence of vegetation increases aeration by increasing the void fraction in a jump roller. And on the other hand, increasing the resistant force and shear stress in the bed reduces conjugate depths and roller length. This increase and decrease depends on the upstream Froude numbers, height and density of vegetation.

Introduction  When a sudden pressure surge is induced in a pipe system, discontinuities like leaks, changes of pipe diameter or material, tee-junctions, local head losses or air pockets, introduce changes in the hydraulic transient event propagation. A leak creates a pressure drop; friction increases pressure damping; a dead-end or a closed-valve reflects totally an incident wave; an air bubble creates a pressure drop followed by a pressure increase.     The detection of these signals allows their identification and location. The information carried in the transient pressure signal can be used to detect, locate and size leaks, and, eventually, to distinguish these from other features existing in the pipeline.   Methodology Physical model     The purpose of this study was to find the location and size of leakage in polyethylene transfer pipes using transient flow. Therefore, a laboratory model was developed for this purpose at the Hydraulic Lab of the Faculty of Engineering Sciences of Shahid Chamran University of Ahvaz.

Forests as Green Belt reduce the height and energy of waves passing through them, reducing their ability to erode sediments and to cause damage to structures such as dikes and sea walls, (Mclvor and et all.,2012). It is well-accepted that wave attenuation by emergent and submerged vegetation is a function of plant characteristics as well as hydrodynamic conditions, (Augustin et al., 2009). (Hirashi and Harada, 2003) showed that the pressure difference on the sides of the green belt is mainly due to drag resistance. this study a new and unique method based on the principle of momentum and direct force measurement has been used to measure wave energy decay simulated by the Green Belt.Most previous studies have been conducted to analyze the wave forces on emergent structures and obstacles. Relative submergence is considered to be the relative roughness of trees and is a factor influencing the resistance of the forest to the passage of waves, (Davoudi et al., 2016). So the resistance of the canopies in the submerged state is one of the important factors in wave damping. Also, in previous studies, variable still water depth has been considered to create different ratios of submergence, which will change the characteristics of the wave. Therefore, in the present study, decided that the resistance of the canopy against broken waves in the submerged state would be determined by changing the height of the obstacles, which will be examined in this study (Figure 1).Figure 1-- Schematic view of the Rigid vegetation with different relative depth of submergence

Experiments were conducted in the Hydraulic Modeling Laboratory of the Faculty of Water Engineering, Shahid Chamran University of Ahvaz, in a 8.3×0.8×0.55 rectangular flume called Knife Edge Flume. Flume has Plexiglas sidewalls and bed and designed to measure the force exerted by the wave force on the barriers at its shore by means of a dynamic load cell installed between the movable and fixed parts of the flume. At the beginning of the experiments, wooden circular cylinders with 1 cm in diameter, fixed parallel arrangement were placed in the moving part of the flume with constant slope of zero. By changing the height of obstacles and generating breaking waves with constant height the absorption force by the canopies was monitored via an electrical display connected to the dynamic load cell.

The submerged ratio of tree canopies is equal to height of inundation depth to height of trees. Therefore, in the submerged state, the ratio is greater than one, and in the emergent state it is less than one. What is important in this study is that different ratios of immersion with different heights of barriers have been created.

The term “Specific Surface Area” (SSA) refers to the area per unit weight of soil. SSA is a fundamental soil property that can be used as an indicator of soil behavior (Utkaeva, 2007) to explain many of the physical and chemical phenomena of the soil: including fertility-determining components (such as the water holding capacity, the adsorption of plant nutrients, and the amount of organic matter) (Voronin, 1975). Measurement of specific surface area is time-consuming and relatively expensive; therefore, its estimation by routinely measured soil variables is preferred. In the present paper two pedotransfer functions for estimating of total SSA (including external and internal specific surface area) was presented, one a multivariate pedotransfer function based on the standard deviation of the diameter of soil particles and clay percent and second an exponential pedotransfer function based on slope of linear regression equation of logarithmic PSD Curve.

Some events such as scour and deposition in rivers may endanger the stability of the outer bank’s bend and reduce the navigable width of them. So far, different techniques have been developed to control this phenomena such as bottom vanes, submerged groynes, bandal-like structures. In the present study, the influences of non-phase hydraulic jet usage on bed scouring and deposition in a 90 bend has been investigated experimentally. Experiments were conducted in a experimental channel to measure the variations of bed topography under a clear water condition. The90 bend is connected to an upstream straight reach 5 m long and a downstream straight reach 3 m long. The channel was rectangular having 70c m width and 280cm radius of bend to centerline. (R/B=4; where R=radius and B=flume width). Four Froude number values including 0.37, 0.41, 0.45 and 0.47 with a constant flow depth of 11cm under clear water condition were used for each test. Bed topography was measured with a laser meter and contour lines were plotted with the Tec plot360software. The scour geometry in a bend depends on channel geometry (channel width, channel , radius and bed slope), flow conditions (depth and discharge or velocity), non-phase hydraulic jet characteristics (length, angle with bank, location in bend), sediment properties (specific gravity, grain size), and fluid parameters (density and viscosity). Therefore, by Using the Buckingham theory and after eliminated the parameters with constant values, the important parameters were q/Q, D/h , Fr and α.Three-dimensional (3D) velocity components were measured using the electromagnetic velocity meter JFE ALEC model ACM3-RS in tests with and without an installed non-phase hydraulic jet. The sampling rate was 20 Hz and time of sampling was 60 seconds. So the minimum 1200 data were collected for each point and their mean was used for determine the 3D flow pattern. The results showed that with installing non-phase hydraulic jet, the maximum scour depth is reduced as much as 77%, 82.7% for Froude numbers equal to 0.37 and 0.41, respectively. It was also found that generally the scour depth occurs away from the outer bank and it was shifted toward the middle parts of the section in the main experiments, which can positively result in the increase in the navigable width and also sediment deposition was observed at the outer bank in some experiment. The results show that non-phase hydraulic jet significantly modified bed topography and reduced the maximum scour depth in outer bank. In this paper to evaluate the effect of space between porous tube and outer bank , three different space (D=0,2.5 and 8 cm) were used. It was found that by decreasing the space between outer bank and porous tube the amount of scour decreases and the maximum scour depth reduced as much as 87.9%, 54.5% and 15.15% for space equal to 0, 2.5 and 8 cm, respectively and it is most efficient when it placed on outer bank. Maximum scour was usually saw near the outer bank, and attributed to the maximum stream wise velocities that occur near the toe of the bank , also the analysis of data have shown that the presence of non-phase hydraulic jet caused uniformity in the velocity distribution at upstream and the high velocity zone moved toward the center of the channel and inner wall. The installing a non-phase hydraulic jet on the outer bank of bend, by its rising velocities, generated a secondary flow that rotates in the sense opposite to the curvature-induced secondary flow. The jet-induced secondary flow cell causes an inwards shift of the cores of maximum streamwise velocity and maximum vertical velocity impinging on the bed, that both of them play an important role in the cour in the outer bank.

Any structure that is in the flow path and establishes a simple, specific and definite flow relationship and depth around it is called a flow controller. Weirs are structures that raise the water level behind them and create control sections and are simple means of measuring discharge. Bazin & Schwalt (1898) were the first to conduct experiments on rectangular broad crested weirs. Since then, many researchers have done a great deal of research on a variety of weirs. Among them we can mention: Woodburn (1932), Tracy(1957), Smith(1959), Abou-seida & Quraishi (1976), Hager&Schwalt (1994), Sargison & Percy (2009),….Due to the importance of flow measurement in open channels, the purpose of this study was to investigate the hydraulic performance of inclined weir, to determine the discharge conveyancecoefficient in this kind of structures in free and submerged flow condition, and to provide relationships to predict the discharge conveyancecoefficient.

Based on Equation 1, we can determine the weir discharge. In this equation Q is the discharge (m3 / s), Cd is the discharge coefficient (no dimension), B is the weir length (m), g is the acceleration (m / s2), and H is the height of the water over the weir (m).Also rewrite from the equation 1 to form 2 by defining it   as the discharge conveyancecoefficient (Mohamed, 2010):In this study, the equation 2 is based on the calculation of the discharge throughput on weirs. The following two equations for free and submerged flow are presented using dimensional analysis.The experiments were conducted in a plexiglass flume (Fig. 1) made of the British ArmField Company with a length of 15 m, a width of 30 cm and a height of 50 cm. A total of 60 experiments (30 free-flow and 30 submerged-flow experiments) were performed on the inclined weir.

A) Free flow condition
In this series of experiments, with increasing H/Lw ratio, the discharge conveynce coefficient of all three sloping weirs increased, but the coefficient of conveynce discharge of rectangular broad crested weir decreased (Fig. 1). This figure shows that among inclined weirs are most sensitive to H/Lw changes.Also comparison of the inclined weir with the rectangular broad crested weir indicates that the rectangular broad crested weir later is less sensitive to H/Lw. Equation 5 was derived to calculate the discharge conveyancecoefficient (Cf) in inclined weirs under free-flow conditions. B) Submerged flow conditionMultiple regression was used to investigate the interaction of the extracted dimensionless parameters on the discharge conveyancecoefficient and to provide a mathematical relation to predict these values. Equation 6 was derived to calculate the Cs coefficient in inclined weirs under submerged flow conditions. Figure 2 shows the computational and observational Cf, Cs in free and submerged flow conditions. The scattering of these points relative to the 45 ° line shows that the correlation coefficient of the experimental and computational values for free and submerged flow are equal to 0.9 and 0.91 respectively.

The results show that:- Increasing in H/Lw ratio leads increases in discharge conveyance coefficient of all three sloping weirs and decreases in rectangular broad crested weir. - For a constant value of the H/Lw ratio, the highest discharge coefficient is related to the upstream and downstream slope weir model (SCW-UD-1) and the lowest discharge coefficient is to the upstream slope weir model (SCW-U-1).-The upstream and downstream slope weir are most sensitive to H/Lw changes and rectangular broad crested weir is less sensitive to changes in H/Lw ratio. - As the H/p < /em> ratio increases, the discharge conveyance coefficient of all three sloping weir models increases.

Weirs are usually constructed by concrete and are impervious so that the water can only flow above the crest. In this between, Gabion weirs with instinctive characteristics including stability, conductivity and economic justification are strongly advised. In this study, the effects of material size, upstream and downstream slopes were investigated on the discharge reduction factor of gabion crump weirs under submerged flow conditions. For this purpose, 8 models of gabion weirs and 3 models impervious weirs constructed in a horizontal flume with 15m long, 0.3m wide and 0.5m deep. The tests were carried out for different variables, including discharge, upstream and downstream depths, material size and upstream and downstream slopes. The results showed that the flow reduction factor decreased as the ratio of the upstream depth to the downstream (Y2/Y1) increased. For a constant ratio of Y2/Y1, the flow reduction factor decreased when upstream or downstream slope increased. It was found that the material size has no significant effect on the flow reduction factor. Based on regression analysis, an empirical equation was developed for estimation of the flow reduction factor which its correlation coefficient variation was in the range of 0.79 to 0.96.

Polyethylene pipes are widely used in pressurized water systems. In the design and interpretation of the ram-trapped signal for diagnostic purposes, viscoelastic behavior of polyethylene tubes should be taken into account.The aim of this study is to detect leakage, and experimental and theoretical comparison of pressure wave velocity and over pressure of transient flow in polyethylene pipes with different Reynolds number. To achieve the objectives of this paper, a physical model was developed in laboratory of the Faculty of Water Sciences Engineering of Shahid Chamran University of Ahwaz and developed two different models of control and a leakage system was and were conducted a number of water-hammer tests. The leakage accuracy in this model increased with increase of Reynolds number. The highest and the lowest percent of the relative error for computational and experimental leakage were estimated 48.8% and 2.02 through a leak hole of 5 mm for experiments with Reynolds numbers of 1282.76 and 12973.55, respectively. Also, this inaccurate study shows the relationship between the theory of compressive velocity and overpressure in the polyethylene transfer pipes, so that the compressive velocity obtained from theoretical relationships is less than its actual value, as well as the relative error of the overpressure in leakage experiments Increasing the Reynolds number increases between the amount of the laboratory and the theory.

A normal way to dissipate energy of the dam released high velocity jets is to allow them to free-fall in to a plunge pool or impact a plane surface in case of dam site limitations. The water jets have an undisturbed core from nozzle outlet to a certain falling height, which has more impact force and less turbulent intensity than the developed part of the free jet. Experiments are conducted to determine core impact pressure coefficient of a vertical jet on smooth and rough plane surfaces. The experiment results for different jet diameters and falling heights showed considerable increase of the mean dynamic pressure coefficient with increase of the jet Froude number for both smooth surface and rough surface. A simple Froude based mathematical model is correlated for estimation of jet core impact force on the smooth and rough plane surfaces. In addition, a considerable increase of the jet core length was indicated with increase of the jet Froude number. Results also showed a strong correlation between turbulence intensity coefficient and the jet core length.

Destruction of bridges caused by scour and other natural phenomenon brings about financial and life losses. Hence, researchers have been studied extensively the scour mechanism and methods of scour countermeasure. Usually scour at bridge occurs both around piers and abutments. Melville (1992)'s study showed that 70 percent of the failure of bridges in New Zealand was due to the abutment scour. Studies conducted on the failure of 383 bridges in the United States showed that in 25% of them the pier scour, and in 72% of them the damage was due to abutment scour (Kayatrak, 2005). The main cause of the abutment scour is due to complex flow vortices which developed around the abutment. Therefore, during the past decades many measures have been developed to protect the bed material against erosion. These techniques can be categorized in two types of covering methods and flow altering techniques. Design guidelines for some of these mitigation techniques can be found in Melville and Coleman (2000). For existing bridges the common practice is to use armoring materials around bridge abutment. Riprap, gabions, rectangular concrete blocks and tetrahedron frames concrete elements are the most effective material for covering and stabilizing the bed around the bridge abutments. In rivers with high flood discharge, the covering material are subject to high flow velocities and therefore large size of rocks have to be used. When the site construction is far away from mountain area or large sizes of the rocks are not available or too costly to transport, other material should be applied. In the present study, a new concrete element-six –legs concrete (SLC)- beside using of smaller size of rocks have been studied to find out the best combination for protecting bridge abutments against scour.

The present research deals with the introduction and simulation of viscoelastic effects in transient flows in polymeric pipes widely used in pipe network. The viscoelastic properties result in appearing newterms in transient flow governing equations which are generally absent in available models. In this study, the governing equations are rewritten and manipulated for considering the viscoelastic properties. The equations are then solved using the method ofcharacteristics coupled with the finite difference method. In order to calibrate the unknown parameters including the unsteady friction and creep coefficients as well as to verify the model, a model of viscoelastic pipe network was made at the hydraulics laboratory of Water Sciences Engineering department of Shahid Chamran University. The configuration of the experimental set-up consists of a pipe network with six square loops, having each loop 3m×3m. The pipes are made of PE with 50 mm nominal diameter and 5.5 mm of wall thickness. The data of dynamic pressure oscillation during these transient events were collected by Pressure transducers. Appling the inverse transient analysis method and with the aid of a genetic algorithm, the friction and creep coefficients of the experimental pipe are determined. The results show that the classical water hammer solver cannot accurately analyze the transient flows in polyethylene pipes. In fact, modeling both dynamic effects of unsteady friction losses and viscoelasticity for such pipes is quite necessary. However, it is also found that the viscoelasticity is obviously more effective than the unsteady friction effects in formation and attenuation of transient signals so that, considering onlyviscoelastic effects would result in acceptable responses.

In this study, energy loss in chutes with cubic submerged obstacles is investigated. The advantages of this method over previous methods such as stepped spillway are lower risk of cavitation. FLUENT finite volume software was used for the numerical computation. The flow was considered turbulent and incompressible. The turbulent model of k  (RNG) was used in this study. In general, for the range of discharges in this study, the energy lost varies from 11% in 1:4 slope to 66% in 1:5 slope for witness models. The results of energy lost in blocked-bed models showed a linear decrease with a relatively steep slope. In general, the “relative energy lost” was shown to be the most in 1:4 slope and the least in 1:5 slope. Moreover, the energy loss relative to upstream energy varies from 83% in models with 1:4 slope to 45% in the blockedbed models with 1:8 slopes. Also, energy loss in blocked-bed models has been increased from 18 to 41 percent in comparison to the witness models. Using multivariate regression, some equations was developed to estimate energy lost.

Distribution pattern of the river bed particles grading creates important issues in investigation of the hydraulic, geomorphological and ecological behavior of the river.. For example, surface grain-size variability is crucial for illustrating sediment transport (Hoey and Ferguson, 1994; Russ, 1999; Joyce et al., 2001).
Particle size characteristics that are dependent on particle size distribution are estimated in different ways, such as sieving method, sampling techniques in the field, photographic print method, and the other methods that have been suggested so far (Aberle and Nikora, 2006). The most prevalent method is the sieving method that obtains particle size distribution curve using cumulative weight of passing aggregation,.. It is obvious that, measurement of the particle size distribution based on field methods are time consuming, overwhelming and non-economic, so developing a fast and accurate method for measuring the particle size distribution of the river bed has a significant effect on civil and environmental engineering. Nowadays, this process is possible using image processing methods to automatically extract particle size using digital images of river bed. Various methods have been reported which aim to provide robust and automated estimates of grain size from images, falling under two broad categories classified by (Buscombe et al., 2010) as, respectively, ‘geometrical’ and ‘statistical’. Both techniques require imagery where the smallest grains are resolved by at least a few pixels. Statistical methods characterize grain size using a measure sensitive to image texture. These approaches have used autocorrelation (Warrick et al., 2009), semi variance or one of the several other methods, including fractals (Buscombe, 2013) and grey-level co-occurrence matrices. Geometrical methods use image processing techniques (principally, threshold and segmentation) to isolate and measure the visible axes (or portions of whole axes) of each individual grain (e.g. Graham et al., 2005; Chang &Chung, 2012). This research showed that new methods of image processing have an adequate potential to replace with previous traditional methods. Also, the percentage of human bias in methods such as field sampling or Sticky layer is very high for sampling of the Armor layer of the river bed, while the image processing method has enough power to take all the details and analysis of the data and it has a desirable accuracy compared to traditional methods.
This research, with using image processing toolbox in MATLAB software, tried to improve the detection filters and finally determined the size distribution of sedimentary particles of armor layer in the alluvial river bed.

Stilling basins are the most common structures for energy dissipation downstream of spillways. A properly designed stilling basin can ensure 60–70% dissipation of energy in the basin. The purpose of this study is to evaluate the performance of perforated end sill and effect of the sill on characteristics of hydraulic jump. The perforated sills with different heights and four ratios of opening 12, 25, 50 and 75% were tested for three tail water depths. Results of experiments confirmed significant effect of the perforated sill on dissipation of energy, reduction of the basin length and reducing dependence of jump location on tail water depth. Based on experimental observation, in a constant Froude number, decreasing of the tail water depth causes the hydraulic jump to move forward toward the end of the basin. In this case, to control the jump and to avoid the hydraulic jump being swept out of the basin, sill distance is decreased. Also, observation showed the sill height needs to be increased as inflow Froude number increases and tail water decreases. In the other words, relative sill height increases up to 30% as tail water depth ratio decreases from 1 to 0.8. Furthermore, the results showed that sills with the 50% opening in comparison with other openings have most effective in energy dissipation and reduction of the hydraulic jump length. The comparison of stilling basin with perforated sill and free jump indicated that the sill with perforation ratio of 50% dissipated 60–90% of water energy in inflow Froude number range of 4.5-12. Moreover, once Froude number increases from 4.5 to 12, stilling basin length increases about 19% for this perforated sill in the tail water depth ratio of 1.

Stilling basins and hydraulic jumps are designers’ favorable choice for energy dissipation downstream of spillways and outlets. A properly designed stilling basin can ensure considerable energy dissipation in the short distance of a basin. In this study, experiments have been conducted to evaluate effects of a perforated sill and its position on the length of a favorable B-type hydraulic jump in a stilling basin. Perforated sills with different heights and ratio of openings were placed in different positions of the stilling basin. Tests were carried out for three tail water depths to assess the sensitivity of the jump to tail water. The hydraulic characteristics of the jump were measured and compared with continuous sill-controlled and free hydraulic jumps. Results of the experiments confirmed significant effect of the perforated sill on dissipation of energy and development of the jump in a shorter distance. Results are also presented in the form of mathematical models for estimation of the sill height, sill position, and basin length with the inflow measurable parameters of depth and velocity.

Rectangular orifices are considered as a common structure for discharge measurement in hydraulics. The purpose of the present research is to investigate the effect of the ratio of length to width of rectangular orifices with same surface area on discharge coefficient. Different rectangles are examined as orifice while the aspect ratio in one of them is equal to 1.618 (golden ratio). Golden ratio is a special number which can be frequently existed in nature and this study attempts to find the probable specialty of this ratio in hydraulics. So, the experiments were carried out on five rectangle orifices that the ratio of length to width of ones varied from 1 to 16. Also, a comparison between the discharge coefficient of rectangular and circular orifices is performed. Therefore, the number of 94 tests was conducted on the orifices in the discharge range of 0.136 - 0.637 L/s. A mathematical relation is developed as pressure distribution coefficient in order to account the effect of non-hydrostatic pressure distribution under low head condition. Results of the experiments showed that the increasing of aspect ratio generally leads to increase discharge coefficient so that discharge coefficient of orifices with variation of the ratio of length to width changes about 11.7%. Furthermore, it is illustrated that golden ratio doesn’t have any specialty in flow evacuation and the discharge coefficient of circular orifices is equal to minimum discharge coefficient of rectangular orifices.

Wave attack is the main source of irreparable damages to the sea coast line. The coastal protection techniques are now improved from structural protection to biological ones. This includes plantation of trees and development of vegetation canopy (called green belt) along the shorelines and protection of coastal structures against the waves created by tsunami. For this¡ the application of green belt has been studied and effect of vegetation density and wave height on wave force is evaluated for waves in broken condition. Experiments were conducted in a flume with 8.3m length¡ 0.8m width¡ and 0.55m height. Experimental variables include four bed slopes¡ four vegetation densities¡ and 110 wave heights. The results show that absorption of wave force increase with increase of wave height and density of vegetation. At the highest vegetation density the wave force effect was reduced by about 75% compared to the case without vegetation.

The security and stability of dams for flood passing through the spillway should be provided. So, kinetic energy of flow over large spillway must be dissipated. One of the energy dissipation structures at downstream dams, are plunging pools. The aim of this paper is to investigate dynamic pressure that is created by the impact of a series of rounded non-submerged jets on a flat plate with the roughness height of 0.8 cm in the angles of the impact of 30, 60 and 90 degrees. This research uses sensors to measure the instantaneous pressure (Pressure transducer) with the ability to record and store the dynamic pressure oscillation of water jet. The results showed that increasing the drop height, average coefficient of dynamic pressure decreases. The extreme dynamic pressures coefficient increased with increase fall height. The mean coefficient of dynamic pressure increases with increasing discharge. As the angle of the impact jet decreases, the dynamic pressures reduce. Also, the roughness increases the dynamic pressure up to 70% in the test interval.

Aim of this study is to measure shear stress in smooth rectangular and trapezoidal open channels. A new approach is presented to measure direct shear on wet perimeter of open channels. A water flume with a section on a frictionless support (called knife edge flume) along with a system of load cell was used to measure total force on the wet perimeter. The local boundary shear stress in rectangular and trapezoidal cross sections was measured using a 4mm diameter Preston tube connected to a differential pressure transducer and a data acquisition system. The calibration curves proposed by Patel were used to convert the pressure readings to shear stress. Local and total shear measurements were used to differentiate the channel wall and bed shear forces. This method allows minimizing of the error as result of the Preston tube diameter. Comparison of the results confirmed advantage of the momentum method over the energy method in term of accuracy. Results are presented for smooth rectangular and trapezoidal channel cross sections with side slopes of 1, 1.5, and 2.

In many cases the collection of obstacles stand against water flow direction and by passing water through these obstacles, vortexes are created in downstream of them and by overlapping of these vortexes, surface waves perpendicular to the flow direction are formed. In this study the impact of obstacle shape on the characteristics of transverse waves are investigated.For this purpose, cylindrical obstacle and cubic obstacle are used. Discharges 5, 15 and 25 l/s and insertion of obstacles in parallel with ordering of 60*60,60*120,120*120 and 180*180 are considered. Totally 36 experiments were performed. The results showed that the shape of obstacles has high impact on the formation of transverse waves. The maximum amount of relative amplitude (A/H ) (A : The maximum wave amplitude , : depth of flow) was occurred for cylindrical obstacle with amount of 61.10% in arrangement of obstacles of and discharge equal to 5 l/s and the minimum value of was occurred for cubic obstacle for side current collision with amount of 6.00% in arrangement of obstacles of and discharge equal to 25 l/s. Equations for estimating of Strouhal Number were presented, using SPSS software developed. According to presented equations, Strouhal number has direct comparison with (P: Distance between obstacles, : Diameter of obstacles ) in cylindrical obstacles and has inverse comparison in two situations of cubic obstacles.