The use of stepped spillways has been increasingly on the rise due to their low cost and high efficiency. Hence, growing attention has been paid to the studies in this field by dam engineers, however, most of these studies have focused on the stepped spillways with uniform step height at the cost of ignoring non-uniform step heights, which also demand particular attention. In this study, a physical model of Herat Dam for a 1.3-m high stepped spillway with a slope of 19.2 o was used to verify the numerical model. Then, three types of stepped configurations were tested using computational fluid dynamics in the ANSYS CFX software d for the flow range of 1.54£dc/h£16.15. Further, a two-phase flow simulation was carried out h for each configuration and all discharge ranges. The results were compared in terms of flow pattern, energy dissipation and aeration point. The results showed minor difference in terms of energy dissipation for nappe regime flow and marked difference in terms of skimming regime flow.

Weirs are the most important and very applicable barriers built across channels to control the flow of water or change its direction. They are also widely used in current measurement in open channels and many hydraulic engineering studies. The advantage of the semi-cylindrical and circular crested weirs as compared with other structures and measuring instruments is their higher discharge coefficient, stability of flow pattern, non-obstruction by floating materials, simplicity of design, durability, wide applicability and economics. One of the newest and most useful software in the field of computational fluid dynamics is Ansys CFX, which provides fairly reliable results. This software, which benefits from the continuity and momentum equations and the application of a turbulence model, was used to simulate flow over three semi cylindrical weirs with different radii in a laboratory study. After selecting the optimum mesh size for simulating the flow in the multiphase form of the fluid model, the k-ε , RNG k-ε and k-ω turbulence models were used to simulate the flow, and the results of the numerical solution was compared with the collected data extracted from experimenting with the physical models. The mesh size selection was based on the optimum mesh, root mean square error, mean absolute error and the coefficient of determination. The results showed that for cylinder with 4, 6, 7 cm radius, the discharge coefficient ranged from1. 2 to 1. 4. Furthermore, both the flow and the discharge coefficient increased with an increase in the radius. Moreover, the location of minimum pressure on the weir moved upstream with incremental discharge in conformity with previous studies.

In this work, dynamic responses of a WWER-1000 reactor in reactivity insertions are studied using a coupling method. The ANSYS-CFX is implemented for thermal hydraulic study of the core and the point kinetic equation (PKE) is coupled as a FORTRAN subroutine. For transient analysis of the core, the thermal feedback of the fuel is added to coolant, and numerical solver of cylindrical heat transfer for obtaining the irradiated fuel rod temperature profile is also included. In order to investigate the irradiation effect, the fuel and gap properties in burnup with appropriate correlations could be calculated. Using memory management system (MMS) and data transfer arrays, coupling between numerical subroutines is carried out. It is shown that the dynamic response of the core depends on burnup, and the response could be varied in time. In addition, the coupling method is reliable for other dynamic calculations.

A stepped spillway consists of steps that start from near the crown and continue to downstream heel. Generally, the amount of energy dissipation in stepped spillway is more than the one of flat spillways (with no steps) with the same dimensions. The high amount of energy dissipation caused by steps allows reducing the depth of drilling of downstream stilling basin, length of stilling basin, and the height of sidewalls. This way, a considerable economic saving is achieved in the implementation of dams. Since spillways help reduce flow rate and increase intake airflow rate, they can be referred to as a combination of a spillway and an energy dissipater. Some of the studies on stepped spillways are as follows: Launder and Spalding (1972); Olsen and Kjellesvig (1998); Chen et al. (2002); Tabbara et al. (2005); Dermawan et al. (2010); Sori and Mojtahedi. 2015; Haji azizi et al. (2016) So far, the studies on stepped spillways have been mostly on experimental and physical models. However, experimental and physical models are costly and sometimes have limitations such as required space and a large number of tests. This necessities consideration of further mathematical and numerical models. Several numerical models can be introduced to analyze flow on a stepped spillway. CFX is one of the numerical models. CFX has been known as one of the most robust software for fluid flow analysis and heat transfer. The finite volume method (FVM) is a numerical method to solve the governing differential equations, which is capable of simulating complexities of a turbulent flow on a spillway appropriately. On the other hand, CFX numerical model uses the coupled model, which increases the speed to achieve results considerably as compared to other numerical models. This research aims at simulating a stepped spillway using CFX numerical model and assessing the amount of energy dissipation under geometric parameters (such as spillway height, spillway gradient, number of steps, and height of steps) and hydraulic parameters (such as flow rate). The difference between this research and other studies can be attributed to the coherence and correlation in studying various components (geometric and hydraulic parameters) and the ability of CFX numerical number in replacing some of the costly and time-consuming tests.

Intakes are one of the varied types of channel and river-water-intake structures. The experimental model is first simulated through ANSYS-CFX software. The verification results indicate that the results of the numerical model correspond fairly well to the results of the experimental model. using a set of experimental data and a numerical model, an artificial neural network has been designed to predict the velocity field within 30, 60 and 90 degrees deviation angles. The comparison shows that the ANN model has an acceptable level of accuracy in predicting the velocity field of the flow. The sediment flow of the experimental model was then numerically simulated with regard to the results in order to examine the sedimentation of the flow. Among the main parameters which affect the flow, the effects of diversion angles, intake discharge ratio were examined on the ratio of the sediment entering the weir and they were compared with the experimental results. The results were fairly consistent. In a constant diversion ration, the ratio of the sediment entering the weir increases as the diversion angle increases and the amount of the sediment entering the weir increases as the intake discharge ratio increases due to the increase in the velocity while the flow depth is constant and the sediments are being increasingly transferred in the weir. Also, as the intake Froude number increases, the ratio of the sediment entering the channel decrease for a constant intake discharge.

Entering turbidity current through reservoir dams and its sediment deposits by the dam body, it not only reduce dam's efficient life but also reduce effective reservoir volume, block intake structures (gates) and damage power-plants. One of the procedures for controlling turbidity current and its erosion through reservoir dams is to create barriers. So in this research, it is evaluated the impact of applying plate barriers and zigzag columnar barriers with tilt angles of 45, 60, 90 degrees against the dam body by using ANSYS-CFX software. the obtained results from a simulation indicates that in subcritical turbidity current, columnar barriers (with relative height of 0.52 equal to the flow depth and with zigzag arrangement) can cause a 60% decrease in discharge flow of turbidity current, and a 5 -fold increase in the density of the barricades, the discharge rate of the turbidity current is decreased by 6%. Furthermore, applying plate barriers with relative height of 1.26 equal to flow height and with deviation angles (tilt angles) of 45, 60, 90 degree to the floor can take under control 50 to 80 percent of the turbidity current. In some cases which it isn' t possible to use the plate barriers because the high altitude is required, it can be applied the column barriers with zigzag arrangement and low height. As well as if barriers are installed in perpendicular position (90 degree) to the turbidity current direction, it will be more efficient than installing barriers with the above-mentioned length in tilt position.