Now showing 1 - 10 of 28
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    Control of sediment inflow into a trapezoidal intake canal using submerged vanes
    (01-11-2018)
    Kalathil, Sruthi Thazhathe
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    Wuppukondur, Ananth
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    Balakrishnan, Ranjith Kannankattil
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    Intake canals are used to withdraw water from rivers for various purposes. Sedimentation in the intake canal reduces the quality and quantity of water being delivered. In this study, experiments were conducted to control sediment entry into an intake channel using submerged vanes in a physical model with a rectangular mobile-bed main channel and a trapezoidal rigid-bed intake channel diverting at an angle of 45°. The variables in the study included vane angle, number of vane rows, and vane spacing in terms of mean flow depth in the main channel. In addition to the commonly used vane array with uniform vane heights, three other vane-height configurations were also tested. The least local scour around vanes and highest sediment reduction (~70%) were observed for vanes oriented at a 15° vane angle with an increasing vane-height configuration placed in two rows. It was also observed that control of sediment entry into the intake canal increased with an increase of both vane spacing and number of vane rows.
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    Review of step-pool hydrodynamics in mountain streams
    (01-10-2019)
    Kalathil, Sruthi Thazhathe
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    Step-pools are one of the major types of bed morphology prevalent in mountain streams. They have a unique flow structure as compared to low-gradient streams, in terms of large boundary elements and alternating super-critical and sub-critical flow conditions, which result in a non-uniform flow regime. Step-pools may also be constructed artificially to restore mountain incisions, and for creating close-to-nature fish passes. For hydraulic model development and various design considerations, the accurate prediction of flow phenomenon is required. This necessitates a detailed study of the turbulence phenomenon in natural step-pool reaches and its effect on the total flow. However, the influence of aerated conditions in step-pool hydrodynamics has not yet been adequately addressed. This paper presents a review of the mechanism of flow resistance and energy dissipation in step-pool mountain streams. Also, the significance of incorporating air entrainment in flow analysis, limitations and the way forward in modeling air–water flow in laboratory studies are discussed.
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    An experimental study to control bed erosion at river confluence
    (22-06-2016)
    Wuppukondur, Ananth
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    River confluence is a region of merging of two flows of different flow characteristics and sediment loads that result in complex hydrodynamics. The momentum transfer from lateral flow and the flow acceleration causes flow constriction resulting in bed and bank erosion. In this study, circular pile models are suggested as scour reducing structures at river confluences and are studied experimentally. From the scour depth contour maps, it was observed that the bed profiles are remarkably modified with installation of the pile models within the confluence. The scour depth was reduced by 28% with installation of pile models of 12mm diameter at a spacing of 2h. When pile models of 8mm diameter are placed at 2h spacing, the scour depth decreases by 26%. Therefore, the present study shows that pile models are effective for reducing bed scour and possibly bank erosion at confluences.
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    Oscillation responses and wake modes of three staggered rotating cylinders in two- and three-dimensional flows
    (01-10-2018)
    Behara, Suresh
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    Ravikanth, B.
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    Kotteda, V. M.Kurshnarao
    Oscillation responses and wake modes of three staggered rotating cylinders, free to move in streamwise and transverse directions, are numerically studied in two- (2-D) and three-dimensional (3-D) flows. 2-D computations are carried out for Reynolds number Re = 60-150, employing the following rotation rates (α), respectively, for the upstream, upper, and lower downstream cylinders: 1, 1, 0; 1, 1, 1; 1, 1, −1. Here, the clockwise rotation is positive. 3-D simulations are performed at Re = 2000 and reduced velocity, U* = 2-11, with the three cylinders being rotated at α = 1. Bell-shaped amplitude profiles are observed for all the rotating cylinders, indicating that the bodies undergo vortex-induced vibrations. In 2-D flow, the considered Re regime can be categorized into three distinct regions, based on the oscillation and frequency responses. Cylinders exhibit negligible amplitudes in the first region, whereas the second region is characterized by high amplitude lock-in oscillations for all three cylinders. In the third region, the downstream cylinders exhibit lock-in response in certain rotation configurations. The oscillation responses and wake modes appear sensitive to the direction of rotation of the lower downstream cylinder for the streamwise and transverse gaps of 5 diameters (5D) and 3D, respectively, between the cylinders. Depending on the rotation configuration, 2S, P, and P + S modes of primary shedding are observed. In 3-D flow also, the cylinders exhibit bell-shaped amplitude profiles, contrary to the galloping response noticed for isolated rotating cylinders in few previous studies. Higher and lower amplitude oscillations induce stronger and weaker 3-D flow instabilities, respectively, in the wake region.
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    Numerical study of ship induced bed shear stress
    (01-01-2020)
    Gopichand, Malasani
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    Pradhan, Tapas Kumar
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    Murali, K.
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    Vessel movement in waterway disturbs flow field around and beneath the vessel. It creates turbulence in water between vessel and river bed resulting in sediment suspension. Erosion of sediment from river bank and bed occur due to orbital motion of wave field, wave breaking, and propeller wash which causes change in river morphology. This phenomenon is more common and severe in shallow waters where movement of high draught vessel exists. Currents generated due to vessel movement carry the suspended sediment and may deposit at low velocity zones. Existing sediment transport models consider shear stress excess to estimate the sediment load. However, these models neglect the shear stress around the vessel. In the present study, wall shear stress due to vessel movement is estimated using STAR-CCM+ (CD-ADAPCO). Volume of fluid (VOF) discretization method is used to solve RANS equations and k-ω SST method to model flow turbulence closure. Vessel movement was simulated using Dynamic Fluid Body Interaction (DFBI) with one-dimension translation (x-direction). Shallow water conditions are studied by simulating h/T of 1.2, where, h is flow depth and T is vessel draft. Model results are compared with empirical equations to predict bed shear stress due to barge tow.
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    Effect of Water Temperature on Suspended Sediment Concentration and Particle Size in Ionized Water
    (01-10-2020)
    Ramalingam, Sivakumar
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    Suspended sediment load to water bodies is governed by climate change and human activities. Fluctuation in water temperature due to climate change affects the suspended sediment deposition. In this study, laboratory experiments are conducted to understand the influence of water temperature on suspended sediment concentration and its particle size in ionized water. Experiments are conducted in an annular flume with kaolin (d50 = 6.9 μm) and ionized water by changing water temperature (30, 40, and 50 °C), bed shear stress (0.01, 0.05, 0.10, and 0.20 N/m2), and initial suspended sediment concentration (1, 2, and 4 g/L). Results show that rise in water temperature causes decrease in both settling flux and degree of deposition, but particle size increases. Variation in initial suspended sediment concentration has an inverse effect on settling flux and has minimum influence on degree of deposition. Size of suspended sediments showed direct relation with initial suspended sediment concentration.
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    The influence of different morphological units on the turbulent flow characteristics in step-pool mountain streams
    (01-12-2021)
    Thazhathe Kalathil, Sruthi
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    The morphology of step-pools is often implemented for ecological restoration and for the creation of close-to-nature fish passes. Step-pools display spatio-temporal variations in bed and flow characteristics due to meso-scale units such as step, tread, base of step, and pool. Exclusive research on the effects of bed variations in step-pools on the flow dynamics is limited. Here, we conducted laboratory experiments on a physical model downscaled from a field site in the Western Ghats, Kerala, India. The results of Kruskal–Wallis ANOVA show significant differences in the velocity and turbulent intensities for the morphological units. A regression equation of the form Power-Allometric1 has been proposed to relate the normalized turbulent kinetic energy with the velocity magnitude. The present study also estimated the range of Reynolds shear stress and energy dissipation factor existent in the step-pool systems. The normalized values of Reynolds shear stress in the x–z plane ranged from − 19.477 to 13.729, and energy dissipation factors obtained for the three step-pool systems are 321, 207, and 123 W/m3; both the results reveal insufficient pool volume for adequate energy dissipation. The study concludes that while designing close-to-nature step-pool fish passes, pool dimensions should be finalized with respect to the target aquatic species.
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    Control of sediment entry into intake canals using submerged vanes with collar
    (01-01-2021)
    Kalathil, Sruthi Thazhathe
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    Murugesan, Muralidharan Rethinam
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    Intake canals transport water and sediments from main rivers to power plants, irrigation fields, and for various other purposes. Increased sediment load in the intake canal leads to reduction in the quality and quantity of water. Submerged vanes are installed at the entrance of intake canals to counteract the secondary circulation and reduce the sediment entry into the intake canals. In the present study, collars have been introduced to submerged vanes to test its performance in the reduction of both sediment entry and local scour around vanes. The vane angles tested are 15°, 35°, 40° and 45°. The ratio of vane spacing to vane height is 5 and the two collar diameters considered are three and four times the vane height, respectively. It is found that 40° is the optimum vane angle for maximum reduction in sediment entry into the intake canal of 85.36%. Collars reduced the local scour and sediment entry (%) by a maximum of 69.08% and 24.84%, respectively, for a 15° vane angle. However, introduction of collar reduced the performance for vane angles 35°, 40°, and 45° in controlling sediment entry into the intake canal.
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    Energy loss in steep open channels with step-pools
    (01-01-2021)
    Thappeta, Suresh Kumar
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    Fiener, Peter
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    Baki, Abul Basar M.
    Three-dimensional numerical simulations were performed for different flow rates and various geometrical parameters of step-pools in steep open channels to gain insight into the occurrence of energy loss and its dependence on the flow structure. For a given channel with step-pools, energy loss varied only marginally with increasing flow rate in the nappe and transition flow regimes, while it increased in the skimming regime. Energy loss is positively correlated with the size of the recirculation zone, velocity in the recirculation zone and the vorticity. For the same flow rate, energy loss increased by 31.6% when the horizontal face inclination increased from 2◦ to 10◦, while it decreased by 58.6% when the vertical face inclination increased from 40◦ to 70◦ . In a channel with several step-pools, cumulative energy loss is linearly related to the number of step-pools, for nappe and transition flows. However, it is a nonlinear function for skimming flows.
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    Determination of suspended sediments particle size distribution using image capturing method
    (17-11-2018)
    Ramalingam, Sivakumar
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    Suspended sediments deposition at estuary affects marine life in coastal ecosystem. Particle size distribution (PSD) is used to find settling velocity of suspended sediments. In this study, a new image capturing system for size analysis (ICS4S) method using digital camera-based image capturing technique for determining PSD is proposed and validated. Image of suspended sediments is acquired using a low-cost setup developed, and ImageJ software is used for image processing. The PSD results obtained using ICS4S method is well correlated with hydrometer test and the Shen method. The proposed ICS4S method is easy to understand and implement both in laboratory and field.