The influence of energy-reducing structure placement on friction velocity distribution in open channel

Abstract

Abstract Energy Reducing Structure (ERS) is aimed at controlling the flow velocity that causes scouring on the main abutment structure of the bridge from its structural failure. It is needed information on the measurement of flow velocity and other parameters of flow, particularly in analyzing the friction velocity and shear stress on the channel bed to identify the effects of ERS placement on the scouring around the abutment area. The experiment was performed in a flume/channel with a length of 8.00 m, a width of 0.40 m, and a height of 0.40 m. The slope of the channel was 0.05% and 0.15%. The type of flow was uniform turbulent flow, using 3 (three) variation of inlet discharge (Q), with and without Energy Reducing Structure (ERS) in the form of a triangular plate with its height determined based on the average maximum rate of 0.6D from the average water surface of 0.06 m from the channel bed. In measuring the distribution of flow velocity with structure, the measurement was conducted in the upstream and downstream areas of the structure, where the structure was placed at x distance of = 4.00 m. Each measurement was performed at the distance of x = 3.50 m ; x = 4.25 m ; x = 4.50 m ; x = 5.00 and x = 5.50 m. The analysis of friction velocity follows the logarithmic law (log-low) applicable to the open channel. The results of the experiment showed that the smallest friction velocity value (u*) was on average happened at x distance = 4.25 m – x = 4.50 m ranging from 0.70 cm/sec – 1.37 cm/sec, as the friction velocity was decreasing. On the other hand, however, the constant of integration (Br) showed great values ranging from 19.27 – 48.79, which implied that the flow rate after passing ERS had the flow velocity beyond the normal range and it would be back to normal after moving away from ERS.

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