Articles written in Sadhana

    • Experimental investigation of local scouring around the bridge piers located at a 90° convergent river bend


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      Placing the bridge piers in the river with a convergent bend can make the flow and erosion pattern complicated around the bridge piers. In this research, the maximum depth and volume of scour hole around piers were investigated in convergent bends of a river. The experimental model with a 90° convergent bend was made with a central curvature radius of 170 cm. The piers with the cylindrical and cubic shapes with different dimensions were prepared and installed at different positions of 90° convergent bend to investigate the scouring condition under three flow discharges in Clear-water mode. On the other hand, natural sand with uniform grain size of d50 = 1 mm was used as the bed materials. The results revealed that depth and volume of the scour holearound piers increase with increasing angle, so that the maximum depth and volume of the scour hole occurred at the angle 75°. Furthermore, the depth and volume of the scour hole around cylindrical piers were lower than cubic piers in all cases. Also, the scour hole shape was asymmetric relative to central axis of the channel and was mainly the extension of the hole towards the inner bend.

    • Numerical and experimental analysis of scour downstream of piano key weirs


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      In the current study, the scour behavior and scour rate downstream of PKWs with rectangular and trapezoidal geometries are investigated and compared for the first time. For this purpose; two experimental models of rectangular and trapezoidal PKWs were constructed and tested at different discharges and threedifferent tail water depths. Three height differences between the sedimentary bed and the weir’s base were considered to investigate the effects of drop height on scouring. The scour measurements showed that the scour hole characteristics increased with the increase in the discharge and the decrease in the tailwater depth in both models. The rectangular PKW model created higher scour depths than the trapezoidal model; however, this difference decreased with the increase in discharge and upstream head. Moreover, as the height difference between the sedimentary bed and the weir’s base increased, the difference between the maximum scour depth of the two models decreased, and their scour profiles became increasingly similar. Numerical modeling of flowpattern under the same hydraulic conditions was used to interpret the scour profiles of rectangular and trapezoidal models of PKWs. Several equations were formulated for predicting the maximum scour hole depth, its location, and the scour hole length downstream of the models based on the regression method, which can help designers with designing and assessing the safety of weirs. In these equations, the most influential parameter is the head difference between upstream and downstream of the weir. The accuracy of the new formulas for score hole dimensions was compared with previous investigations, especially with equations for falling jet scour. More accuracy was achieved for both types of PKWS scour hole characteristics.

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