---

Abstracts This paper presents how the genetic algorithm (GA) can be applied to design of cascade stilling basins. Genetic Algorithm is adaptive method, which can be used to solve search and optimization problems over a period of generations, based upon the principles of natural selection and survival of the fittest ones. The objective of this research is to minimize total cost of construction effectively which is a function of height of falls and length of stilling basins, while fulfilling the hydraulic and topographical criteria. The efficiency of GA discussed here has been tested for a benchmark example and the result for this algorithm is compared with the other method introduced by Vittal and Porey. The results clearly reveal superiority of the GA algorithm

---

Geometry of the chute blocks in stilling basins plays a significant role in size and type of these structures. One of the most influencing factors in the design of the blocks is the fluctuating pressure which may cause fatigue on the blocks. Despite investigations conducted by many researchers, there is not enough information about the pressure fluctuation around chute blocks in compacted stilling basins such as Saint Anthony Falls (SAF) basins. In this paper, the results of a naval experimental work and measurement of pressure fluctuations around chute blocks of SAF stilling basins are reported. The results show that the pressure fluctuations around the chute blocks cannot be overlooked in designing such structures. The variation of pressure fluctuation with Froude number of incoming supercritical flow at various faces of the chute block is reported, which shows an increasing trend of pressure fluctuation. It is also observed that the submergence of hydraulic jump will decreasingly affect the pressure fluctuations. The trend of variations will follow different patterns at the different faces of the block.

---

Hydraulic jumps occur in natural systems like streams and rivers as well as manufactured systems. Samples of the latter occurance are jumps in water distribution and irrigation networks formed downstream of hydraulic structures such as spillways, sluice gates, and drops. These structures are usually designed for a specific tailwater depth. Stilling basins with baffle blocks are frequently used as energy dissipators downstream of hydraulic structures. Baffle blocks are often used to stabilize the jump, decrease its length and increase the energy dissipation. If the flow rates become more than the design discharge, the tail water depth will be greater than the one required for a free jump. These situations are common in low head hydraulic structures including low diversion dam spillways and gates. Under such conditions the hydraulic jump will be submerged.  The performance of the blocks in submerged jump (SJ) condition differs from the free jump (FJ) case. According to some factors such as Froude number, block shape and location and submergence factor, flow regimes on baffle blocks in condition of submerged hydraulic jumps which occurs in stilling basins, are classified into two regimes, the deflected surface jet (DSJ) and reattaching wall jet (RWJ). In this article a numerical study was conducted to investigate flow pattern, vortexes and the magnitude of vorticity in submerged hydraulic jumps with baffle blocks downstream of a sluice gate. The results were compared to ones in same conditions without blocks. 3D RANS simulations have been applied by Fluent software. RSM turbulence model were used which illustrated much precise results in verification. Three numerical models have been created; Submerged wall jet without blocks, submerged hydraulic jumps with baffle blocks in the condition of deflected surface jet flow regime and submerged hydraulic jumps with baffle blocks in the condition of reattaching wall jet flow regime. Flow pattern has been exhibited for each model and results were compared with each other. Vortexes formed in such situations classified into three groups according to axis which they whirl around. It was observed that deflected surface jet regime has more vortexes in comparison to the two other conditions. In addition, by measuring the average magnitude of vorticity in cross-sections it has been concluded that z-vortexes –vortexes which rotate around z axis– much more powerful than x- and y-vortexes as they determine the kind of flow regime. Furthermore, this magnitude is about two times larger in deflected surface regime than two other situations. This fact leads to more turbulence in the flow that makes deflected  surface jet  regime the desirable condition in which baffle blocks perform more efficiently as energy dissipators in comparison to two other investigated models. In order that, from energy vantage point, conditions should be provided in a way to form submerged hydraulic jump as deflected surface jet regime.

---

One of the most frequently encountered cases of rapid varied flow is the hydraulic jump. Stilling basins are used to dissipate the excess kinetic energy of flow to ensure the safety of overflow spillway, chutes, sluices, pipe outlets etc. in this study the topic of block in stilling basins is investigation in a general approach and it’s effect on energy dissipation and downstream scouring are analyzed. In the present research, the energy dissipation and scouring phenomenon were studied in different hydraulic and geometric conditions. Moreover, the present paper was focused on the effect of presence of blocks as an effective parameter on energy dissipation on stilling basin performance. To analyze and assessment of formed hydraulic jump in the stilling basins, the experimental data of many recent researches were achieved and compared. It was concluded that presence of blocks has significant effect on energy dissipation from 1% to 34%. It is also shown that with increasing the Fr Number, the secondary depth increases and the using a rough bed causes reducing the secondary depth between 18% to 37% in comparison with smooth one. Moreover, installing a rough bed also reduced the length of hydraulic jump between 27% to 67%. Using block in the stilling basins, reduces the scouring depth from USBR standard recommendation. Finally, it was concluded that using blocks increased the efficiency of the stilling basin performance.

---

Walls convergence of stilling basins is one of the ways to improve hydraulic jump to increase tailwater depth and energy dissipation at downstream of spillways of high head dams. On the other hand, occurrence of hydraulic jump in converged sections is accompanied with formation of shock waves. Technically, production and development of the mentioned waves are undesirable due to amplification of mixture of water and air and resulting, disturbance outbreak on occurrence of stable hydraulic jump. Many studies have been conducted on the characteristics of hydraulic jump over gradually expanding cross sections, but comparatively few have been carried out on basins with convergent wall. In this research, occurrence of hydraulic jump in stilling basin with convergent wall was studied using experimental model for three different geometry and initial Froude number equal to 3.17 and 4.46. Experiments were conducted in a flume with a length of 6m, width of 1m and depth of 0.7m. Angels of convergence (7.7º and 19.5º) and type of stilling basins walls (straight and curved) were intended as geometric variables. In all experiments, widths of upstream and downstream channels were considered 80 and 40 cm, respectively (contraction ratio=0.5). The flow discharges were measured by an ultrasonic flow-meter having the accuracy of 0.02 lit/s. Values of instantaneous velocity were measured in 10 vertical sections in centerline of the convergent stilling basins using an electromagnetic 2-D velocity meter having the accuracy of 0.5 cm/s. Maximum height of produced shock waves in the contraction sections and conjugate depths of hydraulic jump were measured by a point gauge having the accuracy of 0.1 mm. The measured values of conjugate depths ratio and energy dissipation were compared with the obtained results of analytical equations presented by Sturm (1985) and Montes and Chanson (1998). The average relative errors of calculation of the mentioned parameters were respectively achieved 9.75% and 17.15%. It should be mentioned that the equations tended to underestimate the conjugate depths ratio and energy dissipation values. The velocity and turbulence intensity profiles were demonstrated and analyzed based on the mean values of instantaneous velocity and minor fluctuation of instantaneous velocity. The effects of convergence angle and curvature of basin wall were investigated on changes trend of the profiles. The results showed that changes of the convergence angle has a considerable impact on the conjugate depths ratio, energy dissipation and length of hydraulic jump. As for a constant Froude number, increasing of the convergence angle to approximately 12º was averagely accompanied with decrease of the conjugate depths ratio and hydraulic jump length to the 34.4% and 35.5%, respectively and increment of the energy dissipation to the 33.2%. It should be mentioned that increasing of the convergence angle caused intensification of the shock waves. Moreover, effects of curvature of basin wall were investigated for an equal convergence angle. As regards it had insignificant impact on improvement of hydraulic jump characteristics and difficulty of its implement, so it is not economical. The obtained results of the present research can be very useful for designer engineers.

---

One of the most famous hydraulic phenomena to reduce flow energy is hydraulic jump, which is used downstream of dam overflows in river sections and structures established in irrigation and drainage canals. It is very important to control and reduce the kinetic energy resulting from this phenomenon at smaller distances from the place of formation. Among the examples of depreciation structures, we can mention the roughness of the bed and the construction of stilling basin and making expansion, but it must be said that it causes pressure fluctuations and damage to the bed of the canals and river. The existence of the submerged jet can reduce this pressure fluctuation and change the flow downstream to subcritical. The purpose of this research was to investigate the presence of a submerged jet system on the characteristic of asymmetric hydraulic jump in corrugated beds so that this phenomenon can be controlled and ensure the safety of structures and beds downstream. For this reason, the experiments were carried out in a flume with a fixed peak overflow with a central flow rate range of 26 to 67 liters per second and 3 mutual submerged jet flow rates. This investigation showed that the corrugated bed in the region of gradual expansion has reduced the length of the jump compared to its absence and the changes in the flow depth have also decreased. Also, the impact of the opposite jet in the submerged shape improved this process; So that energy consumption was reduced by 25-30% and jump length by 50%. Therefore, the effective role of this combination of jet system and continuous corrugated bed was shown.
 

---

Stilling basins are used in the outlet of channels, chutes and culverts to dissipate the excess kinetic energy of incoming flow. One of the basins in which the energy of incoming flow is dissipated by impact, is USBR VI stilling basin. The USBR VI stilling basin was first introduced by Bradely and Peterka in 1995 and then was modified by Biechley in 1978. This structure consists of a middle wall and an endsill. Scouring around the structures that are located in the vicinity of erodible beds, such as stilling basins, has always been one of the most important problems related to these structures. Unlike other types of stilling basins, the studies carried out around this type of basin are limited, and there are still many hydraulics features of this type that have not been considered in previous researches.
In this article, the effect of the shape of endsill on scour depth downstream of stilling basin is evaluated. Based on Beichley graph (Standard Design), the physical model of stilling basin was designed, constructed and installed in the hydraulic laboratory of Tarbiat Modares. Experiments were conducted in a 0.8 m wide, 0.9 m height, and 0.8 m length rectangular channel. The pump used in the experiments had a nominal flow rate of 400 cubic meters per hour (about 120 liters per hour), a head of 11.7 meters, a power of 22 horsepower, and an engine speed of 1450 rpm. In the design of experiments, the parameters including approach Froude number (i.e. 1, 1.5 and 2 times of standard Froude number on Beichley graph), the diameter of inlet pipe (i.e. De = 5, 8, and 12 centimeters), and endsill shapes (triangular, stepped and circular quadrant), in the form of 27 tests were assessed to study the dimensions of the scour depth.
The observations revealed that in all three endsill shapes, the increase in Froud number has led to the decrease in scour index. the circular quadrant endsill had the lowest scour depth in the front of endsill and the least scour index, in the range of the Froude number of 2 to 6. In the range of the Froude numbers of 9 to 14, the triangular endsill causes the lowest scour index. In the relative diameter of inlet pipe equals to 10.16, for Froud numbers equal to 9.27 and 13.91, the triangular shaped endsill has the least scour index. in every endsills, decreasing the pipe’s diameter results in the maximum depth of the scour. Another important finding is that sediment bar is only formed in experiments conducted with inlet pipe’s diameter equal to 5cm for Froude number equal to Froude number on Beichley graph. The biggest amounts of the height of sediment bar and maximum scour depth are found for the stepped endsill and the smallest amounts of the height of sediment bar and maximum scour depth are found for the circular quadrant endsill. Subsequently, the non-dimensional equations according to the Froud number of incoming flow and the relative diameter of inlet pipe, were presented to estimate the maximum depth of the scour hole.