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Ziba Fazel, Masoome Fazelian, Dr. Hamed Sarkardeh,
Volume 15, Issue 2 (3-2017)
Abstract

Air-water flow is a complex and challenging subject in many engineering fields as well as hydraulic engineering and discovery of its characteristics can help the engineers to predict and analyze a probable phenomenon. In the present paper, development of a device capable of measuring the flow velocity, air concentration, diameter and counts of bubbles in air-water flows is described. The heart of the present device is two resistive probes with a novel configuration. Being pressure and corrosion resistant and also having negligible resistivity in the flow are some of the unique features of the employed needles. Moreover, sampling frequency and time can be set for the intended application by the user. In the present electronic board, maximum available sampling frequency is in the order of KHz, while the time of sampling is not limited. The circuit is designed with ability for avoiding the polarization of the probe tip. Increasing the number of probes up to four which can operate together and suitable for more complex flows with no change in the electronic board is another advantage of the proposed device. Different tests for verification of the device accuracy have been performed and good results were reported for measurements.


Ramos-Alcazar Luis, Marchamalo-Sacristan Miguel, Martinez-Marin Ruben,
Volume 15, Issue 2 (3-2017)
Abstract

This article presents a new approach to obtain a complete map-type plot of the precisions of TLS equipment based on the direct measurement of time of flight method at midrange distances. Tests were developed in field-like conditions, similar to dam monitoring and other civil engineering works. Taking advantage of graphic semiological techniques, a map in “distance - angle of incidence” coordinates was designed and evaluated for field-like conditions. A map-type plot was designed combining isolines and sized and colored points, proportional to precision values. Precisions under different field conditions were compared with specifications. For this purpose, processed point clouds were evaluated under two approaches: classical "plane-of-best-fit" and proposed "simulated deformation”, that showed improved performance. These results lead to a discussion and recommendations about optimal TLS operation in civil engineering works.


Sohrab Karimi, Hossein Bonakdari, Azadeh Gholami, Amir Hossein Zaji,
Volume 15, Issue 2 (3-2017)
Abstract

Dividing open channels are varied types of open channel structures used to provide water for irrigation channels, agriculture and wastewater networks. In the present study the mean velocity is calculated in different dividing angles within the branches channel through the use of artificial Neural Network (ANN) and coputational fluid dynamices (CFD) models. First the ANSYS-CFX model is used to simulate the flow pattern within the branch with a 90° angle. The results of the CFX model correspond fairly well to the results of the experimental model with Mean Absolute Percentage Error (MAPE) of 5%. After verifying, two CFX model are generated in 30° and 60° angle in different width ratios of 0.6, 0.8, 1, 1.2, and 1.4, and the mean velocities are obtained by flowmeter. Following that ANN model trained and tested through the use of a set of experimental and CFX datas. The comparison showed that the ANN model has an acceptable level of accuracy in predicting the dividing open channel mean flow velocity with mean value R2 of 0.93. Comparing the results indicated that ANN model with the MAPE of 1.8% performs better in 0.8 m width ratio. Also, in this width ratio the MAPE are equal to 1.58, 1.87, and 2.04 % in 30°, 60°, and 90° deviation angles respectively and therefore the model performs better in 30° angle.


Yang Wang, Kai Su, Hegao Wu, Zhongdong Qian,
Volume 15, Issue 4 (6-2017)
Abstract

The reinforced concrete bifurcation in hydropower station is consistently under high internal water pressure, and its diameter is usually larger than common duct junctions. In order to diminish or to decrease the heavy plastic zone and stress concentration, structure rounding is commonly used on bifurcation. This will bring some changes to the flow characteristic of bifurcation, and it is an interesting attempt to figure out the influence of structure rounding optimization. The Realizable k-ε model was employed in Computational Fluid Dynamics numerical simulation. The water pressure distribution was compared quantitatively at several certain sections. Furthermore, uneven pressure is analyzed by relative standard deviation. Hydraulic characteristics are discussed as well, including flow pattern, excavation volume and head loss in different working conditions. The results indicate that the pressure of pipe wall is uneven, and the maximum and minimum pressure value has a differential of 0.3% - 1.2% compared to relative static water pressure. The pressure unevenness will increase after structure rounding, and it has a positive correlation with structure rounding radius. At the same time, it is more reasonable for structure rounding in obtuse angle region than that in acute angle region, on account of well-distributed flow conditions and better economic benefit.


Manoochehr Fathi Moghadam,
Volume 15, Issue 4 (6-2017)
Abstract

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.


Mohammad Hadi Ranginkaman, Ali Haghighi, Hossein Mohammad Vali Samani,
Volume 15, Issue 4 (6-2017)
Abstract

This paper investigates the frequency response method for waterhammer phenomenon in piping networks. The unsteady flow governing equations are solved in time domain using the method of characteristics. They are also solved in frequency domain using the transfer matrix method. For the pipe network under consideration, critical transient excitation scenarios are identified. For each scenario, the frequency responses of the system as well as the time history of the transient pressures at the network nodes are calculated. The model is applied against a real pipe network and the results of the transfer matrix method are compared with those of the method of characteristics. It is concluded that the frequency response method not only presents a very fast algorithm for analyzing pipe systems but also, has an acceptable accuracy compared to the method of characteristics. The frequency response method requires linearization in some terms of the governing equations. Instead of that, it needs no computational discretization and interpolation necessary in time-space domains when using the method of characteristics.


Younes Aminpour, Javad Farhoudi,
Volume 15, Issue 5 (7-2017)
Abstract

Local scour downstream of hydraulic structures is one of the critical phenomena which has absorbed a vast amount of interests by researchers. The designers of hydraulic structures, particularly, spillways try to utilize proper means to minimize the consequences of excess energies downstream of such structures which usually tend the erosion at their immediate downstream reaches. The stepped spillway is designed to create a large amount of energy dissipation by means of steps and would decrease the amount of scour evolution at its downstream. This article presents the results of 67 experiments conducted at two different scales of stepped spillways, to study the local scour downstream the structure. The experiments were planned to consider a wide range of geometrical factors, flow characteristics, and sediment properties. The time length of experiments was ranged from 6 to 24 hours which produced more than 80000 data points for analytical considerations. The results were used to render a regression equation to define the similarity among the scour hole profiles. It was observed that, a long term observation would be needed to reach the equilibrium state. However, semi-equilibrium conditions will be achieved after 24 hours. It was also noted that the depth of scour hole adjacent to channel walls was bigger than that at centerline. 



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