Experimental Investigating on the Effects of Two Obstacles on Behaviour of Turbidity Current

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Naji Abhari m.; IRANSHAHI M.; GHODSIAN M.

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Journal: Modares Civil Engineering journal Year:2018 | Volume:18 | Issue:3 Page(s): 237-249

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Title

Experimental Investigating on the Effects of Two Obstacles on Behaviour of Turbidity Current

Author(s)

Naji Abhari m. | IRANSHAHI M. | GHODSIAN M. | Issue Writer Certificate

Keywords

Turbidity currentQ2

ObstaclesQ1

Inlet Froud numberQ1

Fluid volume discharge per unit widthQ1

Suspended sediment transport rateQ1

Abstract

Turbidity currents account for transporting sediments into reservoirs, seas, and oceans. Its main driving mechanism is the density difference between the sediment-laden and the ambient fluids. This phenomenon may lead to a blockage of the bottom outlet, affecting the operation of hydropower systems and reducing the reservoir storage capacity. Therefore, if the movement of the Turbidity current toward a dam is restricted then the sediment settles down prior reaching the dam at early stages of progressing into dam reservoir, the reservoir storage capacity is preserved for a longer period. The use of Obstacles not only controls the deposition of fine grains at critical locations like in front of intakes and bottom outlets but also improves the reservoir operation from the environmental perspective. So, understanding dynamics of these currents for sedimentation and erosion is very important. In this paper, the effects of two Obstacles on the behaviour of Turbidity currents investigated experimentally. An eleven meters long rectangular channel (11 m×0. 6 m×1. 0 m) with the bottom slope of 0. 25% was used to run the experiments and a 3 m3 tank along with a constant head tank were served as the turbid water supplier. Two triangular Obstacles were installed at predefined locations from the sluicegate. Then the experiments were carried out and the results compared with those from without obstacle condition. Velocity and concentration profiles at the upstream of first obstacle and between the first and second Obstacles are measured by Vectrino at quasi-steady conditions and compared to those of without obstacle conditions showing a significant decrease of velosity in the presence of the two Obstacles specially between the two Obstacles and also at the downstream of the second obstacle. Fluid volume discharge per unit width and Suspended sediment transport rate are calculated based on measured velocity and concentration. Also, the effects of Inlet Froud number on the Fluid volume discharge per unit width and Suspended sediment transport rate was investigated. The results show that presence of Obstacles introduces new regions to velocity profiles and two ponds of Turbidity currents are formed at the upstream of the first obstacle and between the two Obstacles. The hydraulic conditions at these ponds make a suitable condition for the suspended particles to be trapped and hence the sedimentation. Variation of the Suspended sediment transport rate and the Fluid volume discharge per unit width depend on obstacle location. These parameters at the upstream of the first obstacle are directly in proportion to the Inlet Froud number while at the downstream the second obstacle and between the Obstacles are inversely proportional. By decreasing the Inlet Froud number, the volume discharge per unit width increases at the upstream of the first obstacle wheras, the amount decreases between the Obstacles. Also, as the Inlet Froud number decreases, the Suspended sediment transport rate increases at the the upstream of the first obstacle but the value decreases between the Obstacles and downstream of the second obstacle resulting the increase of the trap efficiency. The Obstacles become more effective in controlling the Turbidity currents when the Inlet Froud number decreases. The first obstacle is 1. 8 times more effective on reduction of local sedimentation rate than the second obstacle.

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APA: Copy

Naji Abhari, m., IRANSHAHI, M., & GHODSIAN, M.. (2018). Experimental Investigating on the Effects of Two Obstacles on Behaviour of Turbidity Current. MODARES CIVIL ENGINEERING JOURNAL, 18(3 ), 237-249. SID. https://sid.ir/paper/256902/en

Vancouver: Copy

Naji Abhari m., IRANSHAHI M., GHODSIAN M.. Experimental Investigating on the Effects of Two Obstacles on Behaviour of Turbidity Current. MODARES CIVIL ENGINEERING JOURNAL[Internet]. 2018;18(3 ):237-249. Available from: https://sid.ir/paper/256902/en

IEEE: Copy

m. Naji Abhari, M. IRANSHAHI, and M. GHODSIAN, “Experimental Investigating on the Effects of Two Obstacles on Behaviour of Turbidity Current,” MODARES CIVIL ENGINEERING JOURNAL, vol. 18, no. 3 , pp. 237–249, 2018, [Online]. Available: https://sid.ir/paper/256902/en

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