Abstract An in situ suspension camera in combination with an image-analysis system was developed at NIOZ to measure the in situ particle size of suspended matter. It differs from other methods in that in sit particle size is measured from ∼ 4 μm upwards in a relatively simple and direct way. It can be used in any waters down to ∼ 4000 m depth (with some adjustments to 7000 m) and in water with a suspended matter concentration up to 200 mg·dm −3 . In very clear ocean water the system becomes inconvenient because of the large number of photographs that have to be taken to obtain a reliable size distribution. This paper describes the camera and the image-analysis system and gives some results of measurements in the Scheldt river and estuary in April 1989. These measurements show a continuous size distribution by volume between 3.6 μm and 644 μm and a good agreement of the data obtained with the 1:1 and 1:10 cameras.

In situ observation of flocs in natural waters

Wake-induced vibration of a circular cylinder at a low Reynolds number of 100

The south west coastal zone of Bangladesh have been affected by rampant water logging due to vulnerable climate, silted rivers and stumpy terrain; and introduction of IWRM and TRM at some places of the zone has substantially safeguarded the circumstance. This study aims to assess the benefits achieved due to implementation of IWRM in parts of Khulna and Jessore districts, and investigate some technical aspects evolving TRM. Analyses have been carried out using satellite images, RS and GIS technology, Digital Elevation Model (DEM) and field investigations. A mathematical formulation has been made to assess rate of tidal sedimentation due to TRM and selection strategies of tidal basins. The study comes up with evidences of considerable advancements in regional livelihood i.e. flood resistance, cultivated lands, cultivable area, cropping intensities and food security due to IWRM. Moreover, the technical facts established on TRM would help planners to have vivid perception regarding the process.

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Integrated Water Resources Management (IWRM) Impacts in South West Coastal Zone of Bangladesh and Fact-Finding on Tidal River Management (TRM)

The flow-induced vibration (FIV) of multiple cylinders is a common phenomenon in industry and nature. The FIV and energy harvesting of three circular cylinders in tandem are numerically studied by 2D-URANS simulations in Reynolds number range of 30,000 < Re < 105,000. Simulation results match well with experiments in the tested cases. Four branches of FIV are clearly captured in the amplitude and frequency ratio curves of the three cylinders with roughness, including initial branch of vortex-induced vibration (VIV), VIV upper branch, transition from VIV to galloping, and galloping. It is shown that the vortices from downstream cylinder are strongly disrupted and modified by vortices of upstream cylinder. The third cylinder is almost suppressed in VIV initial branch. The 2P vortex pattern is observed for the first cylinder in the VIV upper branch. For Re = 90,000 in the transition regime, the vortex patterns of the first and second cylinders are 2P + 4S and 2P + 2S, respectively. In the galloping branch, the shear layer motion is in synchronization with the motion of the cylinder, and the maximum amplitude of 2.8D is reached by the first cylinder. The total converted power of the three cylinders increases with U*water both in the simulation and experiment. For the three cylinders, the maximum power reaches up to 85.26 W with the increase of Reynolds number. The energy conversion efficiency is stable and higher than 35% in the starting region of VIV upper branch, and the maximum value of 40.41% is obtained when Re = 40,000.

Research on Flow-Induced Vibration and Energy Harvesting of Three Circular Cylinders with Roughness Strips in Tandem

Flow past a single stationary sphere, 2. Regime mapping and effect of external disturbances

Galloping cross-flow vibration responses of three in-line identical square cylinders are numerically studied for the mass ratio m*=2, streamwise gaps Lx=3B and 5B, reduced velocity U*=3−50, and Reynolds numbers Re = 150 in two dimensions (2-D) and 2000, where the flow is three-dimensional (3-D). Here, B is the side of the cylinder. An isolated cylinder does not gallop since the mass ratio m*=2 is less than the critical value in the Re = 150 flow, whereas for the three in-line bodies, galloping instability is triggered at the upstream cylinder due to the interference effect caused by the presence of downstream bodies. The interaction with the wake of galloping upstream cylinder promotes galloping instability for the two downstream cylinders almost immediately at Re = 150. In the three-dimensional wake at Re = 2000, downstream cylinders interact with less coherent Karman vortices shed by the galloping upstream cylinder, compared to the 2-D case. This phenomenon leads to the delayed on-set of galloping response for the first downstream cylinder, while the second one never gallops.

https://pubs.aip.org/aip/pof/article-pdf/doi/10.1063/5.0146666/17992346/067112_1_5.0146666.pdf

On the galloping cross-flow vibration responses of three in-line square cylinders

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.

Effect of Water Temperature on Suspended Sediment Concentration and Particle Size in Ionized Water

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.

Venu Chandra

Papers

On the galloping cross-flow vibration responses of three in-line square cylinders

Effect of Water Temperature on Suspended Sediment Concentration and Particle Size in Ionized Water

Control of Sediment Entry into Intake Canals Using Submerged Vanes with Collar