JOURNAL OF HYDRAULICS
Year:2019 | Volume:14 | Issue:2 (142) |Papers Count:12

The scour due to jets influence the stability of the base of the dam the downstream structures and may cause them failure. In this paper the results of 40 experiments of scour due to 3D-wall jets are presented. In this research, 3 values of densimetric Froude number in the range of 3. 9-6. 6, 5 values of tailwater ratio in the range of 4-15 and 3 values of the location of the wall jet from the side wall in the range of 0. 5-17. 3 were used. In this research the mechanism of the scour is reported, then the effect of the side wall on scour due to wall jets for different values of tailwatre depth ratio and densimetric Froude number is investigated. According to the results of this research by decreasing the distance of the nozzle to the channel side wall, the jet deviates to the side wall and forms the asymmetrical shape of flow structures as the maximum scour hole depth due to the nearest jet nozzle increases 94% as compare to the jet in the middle of the channel. In addition, the length of the scour hole decreases as the jet goes to the side wall of the channel. In most of the experiments the minimum scour hole length decreases about 13% for the nearest nozzle to the channel side wall as compare to the nozzle in the middle of the channel. In some cases the tailwater depth influences the scour hole length parameters an increases them. According to this research one can concluded that the location of the nozzle affect the scour hole dimensions and should be considered as an effective parameters on scour hole due to wall jets.

The deposition of the sedimentary materials in water reservoirs, especially around the bottom outlet gates, is one of their main operational problems. The efficiency of the sediment discharge from the bottom outlet gates is also very low. In the present study, a new method is proposed to increase the deposited sediments discharge efficiency, in which the so-called SFM1 structure consists of two parallel rows of columns has been installed at the reservoir bed upstream of the outlet gate. One to six pairs of the columns with a permeability of 0%, 28. 6%, 37. 5%, 42. 9%, 50%, and 60% were installed in two parallel rows at relative placement spaces of 1, 2, 4 and 6 times the outlet gate diameter. Non-cohesive uniform sand aggregates with an average particle size of 0. 67 mm were tested as deposited sediment on the reservoir bed. The results showed that the SFM structure considering the best conditions (i. e. a permeability of 37. 5% and relative distance of two rows of 2D) increased the average sediment discharge volume by 161% compared to the control case (reference test without SFM installation).

Spillway is a hydraulic structure that is used for passing excess water and floods from upstream to downstream of dams. The spillways are of a variety of hydraulic structures that are constructed for various purposes in water transfer systems. The lateral overflow is constructed with an elevation less than the height of the wall of the canal, and when the surface of the water rises, lateral overflows will regulate the flow rate and control the water level in the main channel. The tests were carried out in a rectangular channel 10 m long, 0. 6 m wide, and 0. 6 m high and 16 Model piano key weir type A trapezoid with different pillars 10, 15 and 20 cm is conducted. The above-mentioned spillways have been investigated in two cases. The results show that the overflow with a pillar of 15 cm in both cases has a maximum flow rate coefficient in the ratio of 0. 20. 5, the inflow with a base of 20 cm they have the highest flow rate. Also, in similar laboratory conditions, the spillway of a trapezoidal piano key exceeds 4 times the rectangular weir.

A clear understanding of the interaction of bed-form and flow characteristics in natural streams is essential for a variety of ecological and river engineering projects such as river rehabilitation, pollution control, and stable channel design. The present study deals with the logarithmic layer of double-averaged (in time and space) streamwise velocity profiles in decelerating flow, in coarse-bed Rivers. The streamwise velocity profiles were obtained from field measurements conducted in the Haraz and Rostam Abad Rivers. Velocity measurements were collected at 200 Hz and 120 seconds by using an Acoustic Doppler Velocimeter (ADV). In Both cases, the river bed was composed of coarse gravel and cobble, with relative submergences ( 50 h/d ) from 4. 4 to 10. 4. Due to the limitations in double-averaging method application in the Iranian Rivers, the validity of this method was investigated using the logarithmic law and the boundary layer characteristic method. Based on the observations, the flow may be divided into the two different layers: the inner layer (logarithmic layer) and the outer layer. In the inner layer ( 0. 02 z / h 0. 3 ), the double-averaged velocity profiles confirmed the logarithmic law. However, the velocity data deviated from the logarithmic law in the outer region without a particular pattern. The results of this study can help a better estimation of hydraulic parameters in coarse-bed streams, decreasing the cost of the hydraulic engineering plans in rivers.

The impact of submerged vegetation patch on the hydraulic parameters such as flow resistance and sediment transfer is significant. However, a few researches in this field have been reported. Flow within and just above the vegetation patch behaves similarly to the mixing layer rather than the boundary layer, thus at this research, the mixing layer theory to quantify the interaction between flow and submerged vegetation patch was evaluated. Although, the effects of the not fully-developed flow over small patches has not been considered in the canonical mixing layer theory. Accordingly, it is essential to combine a canonical mixing layer model and modified equations to quantify evolving area along the patch. This study used the field experiments to evaluate the applicability of this theory. Field experiments were conducted over vegetation patches with three different densities in Beheshtabad River with rubble bed in Chaharmahal-Bakhtiari province. The results reveal that there is a reasonable agreement between the measured values of velocity and Reynolds stress profile with the estimated ones by evolving mixing layer equations. However, the spreading coefficient of this model is reduced by increasing the canopy density thanks to the limitation in the vertical development of eddies. Quadrant analysis over vegetation patch shows the dominate event under the crest of canopy is “ ejection” and over the crest of canopy is “ sweep” . Moreover, the contribution of “ sweep” event increases slightly at downstream of vegetation patch.

In rivers with a compound section, typically the relatively high roughness of floodplains, as compared with the main channel, cause to flow speed difference between the main channel and the floodplain. The velocity dissimilarity also creates shear layers at the interface point of the main channel and the floodplain. The development of shear layers will also cause turbulence in the mutual plane of the main channel and the floodplain. In such conditions, the average flow speed cannot be applied to compute parameters such as shear stress, bed-load discharge, and so forth. In this research, laboratory experiments were carried out to study the effects of floodplain divergence on flow hydraulic and the rate of sediment transport for different roughness and divergent angles. 36 tests were done at a concrete flume with compound channel cross section (9 and 27 tests with prismatic and non-prismatic cross section, respectively).-The velocity in different sections were measured using a micro-propeller and ADV (with 200 Hz frequency) for depth ratio of 0. 15 and 0. 25 and for depth ratio 0. 35, respectively. . The results reveal that the increase in all three factors of the roughness, divergence angle, and relative depth cause dramatic changes in the hydraulic of the flow and the sediment transport.

present paper investigates the simultaneous effects of the density and pattern of bed roughness with obstacle on the control of a dense current head. The measurements were conducted in a flume (length 720 cm, width 35 cm, and height 70 cm) using two roughness patterns (parallel and zigzag), and with four roughness densities (0%, 10%, 30%, and 50%). In all the tests series, the dense fluid was assumed to be of the salt type with a density of 20 g/lit. Two series of tests were performed using rough surfaces with and without obstacle. In total, 56 tests were conducted. The results showed that in all of the tests with slope, for the zigzag pattern, the highest control for the head of the dense current occurred at a density of 30%; while this density value was 10% for the parallel pattern. Moreover, using an obstacle in addition to roughness increased the control of the density current head. The mean control percentage in the tested slopes was 97% for the zigzag pattern at a density of 30% compared to the mode without roughness and with a zero percent slope. However this mean control percentage increased to 163% by implementing an obstacle. Furthermore, in the parallel pattern with a density of 10%, the mean control percentage for the modes without and with an obstacle were respectively 44% and 74%.

wave impact is the most important force to the marine structures. Breaking waves makes the most severe forces to the marine structure. Due to the turbulence and strong mixing behavior of the breaking waves, its analysis is difficult and complicated. In the present research, first a solitary wave is numerically modeled, and then the propagating of the solitary wave plunging breaker is simulated on the slope beach. The finite volume method and the two-phase VOF model have been implemented for free-surface modeling. The simulation was performed in an unsteady-state using the k-w SST turbulence model. The governing equations of the wave movement were coded in the model. The shape of the free surface of the water is quantitatively and qualitatively in good agreement with analytical and experimental results. All of the different stages of wave breaking including the beginning, the tip-wave collision to the bed, the jet of water formation and its further breaking, are relatively in good agreement with the experimental data. Three-dimensional simulations of a solitary wave impact to a rigid column have been performed. These simulations were separately implemented for two states of breaking and without wave breaking. The results were validated in terms of impact forces.

Sea level rise and groundwater extrapolation lead to freshwater head changes at the boundaries of the coastal aquifers and causes further intrusion of seawater into the aquifers. In the present study, the behavior of unconfined coastal aquifer to instantaneous sea level rise and freshwater head decline is investigated by physical and mathematical dispersive modellings. Three laboratory models have been conducted in a sand tank and salt wedge shape has been photographed over time. Salt wedge toe position, area of transition zone and volume of intruded seawater are measured for this purpose. The numerical results are in a good agreement with the experimental observations. The outputs derived by both modellings indicate that the instantaneous rise of head in sea boundary or significant decline of freshwater head in land-side deforms the wedge shape of saline water, so that the seawater encroachment velocity at its tip will be faster than other regions. Moreover, establishment of an inverse hydraulic gradient (hydraulic gradient from sea to land) causes significant seawater delivery from sea into the aquifer. As a result, the salt wedge can even be stretched up to land boundary. Results of dispersive simulations demonstrate that when the velocity of saline water rises inside the aquifer, the advection role will be highlighted rather than dispersion. However, the longitudinal and transverse dispersivity will also increase which consequently will widen the transition zone. Nevertheless, the increase rate of saline water volume has been achieved much higher than the growth rate of toe position and transition zone area.

Application of simple and accurate routing models in the flood warning systems increases their capabilities. In the present study, it is attempted to fulfil the flood routing using ADZ model with its discrete time form, named transfer function in the three river reaches which are located between six hydrometric stations along the ZARINE and SIMINEH streams. In the reach routing, daily discharges during 15 years (2001-2015) have been employed. Firstly, the numbers of the numerator and denominator terms have been obtained. These parameters are giving the numbers of the subzones in every river reaches and also the conditions of the connections (series or parallel). The results revealed that only one sub reach for every river. Due to this fact, no more analysis of the connection conditions has been done. After that, the values of the transfer function coefficients have been derived using micro CAPTAIN toolbox. The statistical parameters of the mentioned toolbox as ((YIC), (Rt2), and (EVN) for the reaches of the DASHBAND BOUKAN-BOUKAN bridge, ALASAGGAL-SAFAKHANEH, and GESHLAGH bridge-ANIAN bridge have been determined as triple sets of (-5. 241, 0. 879,-10. 86), (-3. 954, 0. 903,-9. 43), and (-2. 792, 0. 920,-8. 139), respectively. The outcomes exhibited a right corresponding between the theoretical graphs, obtained with the transfer function, and observed discharges. The transfer function method is more straightforward rather than the other accurate available methods of flood routing like fully Saint-Venant equations. Therefore, it can be used as an efficient method in the flood routing in the river reaches.