scholarly journals Velocity Field and Turbulence Structure around Spur Dikes with Different Angles of Orientation under Ice Covered Flow Conditions

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1844
Author(s):  
Rahim Jafari ◽  
Jueyi Sui
Keyword(s):  
Flow Characteristics ◽  
Ice Cover ◽  
Roughness Coefficient ◽  
Turbulence Structure ◽  
Flow Conditions ◽  
Spur Dike ◽  
Turbulence Structures ◽  
Scour Hole ◽  
Spur Dikes ◽  
Set Up

Spur dikes are well-known structures that are widely used in rivers and coastal regions. Depending on their types, sizes, and orientation angles, spur dikes can substantially change flow characteristics. Results of previous studies indicate that the presence of an ice cover in rivers can cause complicated flow structures. The present experimental study investigates velocity fields and turbulence structures in the vicinity of spur dikes under ice cover with different roughness coefficients. The spur dikes were set up at the following three angles of orientation, 90°, 60°, and 45°. Our results show that the strongest velocity fluctuation occurs immediately above the scour hole surface and very close to the dike tip. The increase in the dike angle toward upstream, the velocity component values increase, leads to a larger scour hole. Results show that an increase in dike angle of each 10° (from 45° to 90°) increases the scour depth between 5% and 10%, depending on flow conditions. Furthermore, the increase in the cover roughness coefficient and the blockage ratio of a spur dike leads to a further increase in turbulence kinetic energy and 3D velocity components values. The findings of this study imply that the appearance of an ice cover can increase turbulence intensities up to nearly 30%.

Experimental Study on the Effect of Froude Number on Temporal Variation of Scour around a T Shaped Spur Dike in a 90 Degree Bend

2011 ◽  
Vol 147 ◽  
pp. 75-79 ◽  
Author(s):  
Mohammad Vaghefi ◽  
Masoud Ghodsian ◽  
Arash Adib
Keyword(s):  
Experimental Study ◽  
Temporal Variation ◽  
Froude Number ◽  
Average Diameter ◽  
Clear Water ◽  
Spur Dike ◽  
Outer Banks ◽  
The Past ◽  
Scour Hole ◽  
Spur Dikes

In the past few decades, the use of spur dikes for stability of the outer banks of rivers has attracted the attention of hydraulic engineers. Setting spur dikes in the flow’s direction leads to local scour around the spur dike and changes the topography of the bed. This paper deals with the study of the temporal variation of the scour hole and topography of the bed around a T shaped spur dike located in a 90 degree bend. The experiments were carried out in a channel with a 90 degrees bend. Uniform sediments having an average diameter of 1.28mm were used under clear water condition. The effects of Froude number on the amount and the geometry of scour hole around a T shaped spur dike and the time variation of scour were investigated.

scholarly journals Numerical scour modeling around parallel spur dikes in FLOW-3D

2017 ◽  
Author(s):  
Hanif Pourshahbaz ◽  
Saeed Abbasi ◽  
poorya taghvaei
Keyword(s):  
Numerical Model ◽  
3D Model ◽  
Flow Characteristics ◽  
3D Models ◽  
Scour Depth ◽  
Spur Dike ◽  
Accuracy Level ◽  
Bank Protection ◽  
Numerical Research ◽  
Spur Dikes

Abstract. Spur dikes are some structures which are built in the flow path with the aim of changing flow characteristics in order to bed and bank protection in rivers. These sudden changes in properties caused by the existence of spur dikes, produces erosion and sedimentation around them. In this paper, effects of series of parallel spur dikes have been investigated numerically. For this purpose, by using experimental and numerical research results from technical literatures, the numerical model conducted in FLOW-3D commercial software and the data were compared with experimental and SSIIM results. The results showed that Froude number and the ratio of U/Ucr affect the accuracy of the models. As a result, by discharge increasing, FLOW-3D models need to be calibrated again. Also, by using a calibrated FLOW-3D model, calculation accuracy of the scour depth at the bottom of the spur dikes becomes better and the accuracy level in the modeling of the surface morphology improves 7 percent more than SSIIM software in the bottom of the first spur dike, more than 80 percent at the bottom of the second spur dike and approximately 40 percent at the bottom of the last spur dike.

scholarly journals Experimental and numerical investigation of flow over a spillway bend with different combinations of permeable spur dikes

2021 ◽  
Author(s):  
Jinmeng Yang ◽  
Zhenzhong Shen ◽  
Jing Zhang ◽  
Xiaomin Teng ◽  
Wenbing Zhang ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Dissipation Rate ◽  
Water Surface ◽  
Longitudinal Velocity ◽  
Flow Characteristics ◽  
Energy Dissipation Rate ◽  
Bottom Plate ◽  
Dye Tracing ◽  
Spur Dike ◽  
Spur Dikes

Abstract In this paper, the effects of different combinations of permeable spur dikes installed in the bend section of spillway on flow characteristics and energy dissipation rate were experimentally and numerically investigated. The results indicate that The permeable spur dikes installed in the spillway bend appreciably contributes to the improvement on the water surface uniformity, and the water surface uniformity can reach 90.13% with three permeable spur dikes installed in the bend. The permeable spur dike can lead to different degrees of decrease in the time-averaged longitudinal velocity in each zone of spillway bend. Different from previous study, no circulation zone is formed upstream and downstream of permeable spur dike due to the presence of permeable holes, and the flow upstream of permeable spur dikes could be divided into three distinctly different flow modes according to dye tracing. The presence of permeable spur dikes causes the concentration of TKE zone at concave bank of the spillway bend, except for TKE zone immediately next to the bottom plate. The TKE first increases and then decreases with the increase in the vertical distance from the bottom plate of the spillway bend, exhibiting a typical parabolic distribution. The energy dissipation rate in the spillway bend with permeable spur dike was calculated using a modified integral method, and the dissipation rate can reach as high as 21.08% with three spur dikes installed in the bend.

scholarly journals Bridge Abutment Protection against Scouring for Unsteady Flow Conditions

2021 ◽  
Author(s):  
Maryam Khajavi ◽  
Seyed Mahmood Kashefipour ◽  
Mahmood Shafai Bejestan
Keyword(s):  
Unsteady Flow ◽  
Steady Flow ◽  
Clear Water ◽  
Flow Conditions ◽  
Spur Dike ◽  
Base Time ◽  
Bridge Abutment ◽  
Water Conditions ◽  
Scouring Process ◽  
Spur Dikes

The bridge abutment is one of the main parts of a bridge and significantly contributes to bridge stability. This study experimentally investigated the effect of the unsteadiness characteristics of hydrographs on the scouring phenomenon around the bridge abutment under clear water conditions. The ability of the permeable and impermeable spur dikes and their distances from the abutment at its upstream on the control of scouring around the bridge abutment was also investigated. The experimental observations imply that the effect of unsteady flow on the scouring process is relatively similar to the steady flow conditions. The results showed that the base time of hydrographs, the type of spur dikes, and the distance of spur dikes from the bridge abutment were the dominant parameters among the considered parameters in this study on the scouring process around the abutment. The results also revealed that the impermeable spur dike was able to completely eliminate scouring around the bridge abutment for two distances of 2L and 3L (where L is the abutment length) for both steady and unsteady flow conditions.

scholarly journals Hydrodynamic and Hydrographic Modeling of Istanbul Strait

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 710 ◽  
Author(s):  
Mehmet Koşucu ◽  
Mehmet Demirel ◽  
V.S. Kirca ◽  
Mehmet Özger
Keyword(s):  
Mixing Layer ◽  
Flow Characteristics ◽  
Open Boundary ◽  
Roughness Coefficient ◽  
Model Parameters ◽  
Temperature Profiles ◽  
Open Boundary Conditions ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Set Up

The aim of this study is to model the hydrodynamic processes of the Istanbul Strait with its stratified flow characteristics, and calibrate the most important parameters using local and global search algorithms. For that, two open boundary conditions are defined, which are in the northern and southern parts of the Strait. Observed bathymetric, hydrographic, meteorological, and water-level data are used to set up the Delft3D-FLOW model. First, the sensitivities of the model parameters on the numerical model outputs are assessed using Parameter EStimation Tool (PEST) toolbox. Then, the model is calibrated based on the objective functions, focusing on the flow rates of the upper and lower layers. The salinity and temperature profiles of the strait are only used for model validation. The results show that the calibrated model outputs of the Istanbul Strait are reliable and consistent with the in situ measurements. The sensitivity analysis reveals that the spatial low-pass filter coefficient, horizontal eddy viscosity, Prandtl–Schmidt number, slope in log–log spectrum, and Manning roughness coefficient are most sensitive parameters affecting the flow rate performance of the model. The agreement between observed salinity profiles and simulated model outputs is promising, whereas the match between observed and simulated temperature profiles is weak, showing that the model can be improved, particularly for simulating the mixing layer.

scholarly journals Using a roller pump for establishing extra-corporal membrane oxygenation (ECMO) – technical considerations for times of crisis

Perfusion ◽  
2021 ◽  
pp. 026765912199618
Author(s):  
Mirko Kaluza ◽  
Benjamin May ◽  
Torsten Doenst
Keyword(s):  
Flow Characteristics ◽  
Centrifugal Pumps ◽  
Roller Pump ◽  
Silicone Tubing ◽  
Heart Lung Machine ◽  
Surface Irregularities ◽  
Set Up ◽  
Flow Detection ◽  
Silicon Tubing

Objective: The COVID-19 pandemic requires thinking about alternatives to establish ECMO when often-limited hardware resources are exhausted. Heart-lung-machines may potentially be used for ECMO but contain roller pumps as compared to centrifugal pumps in ECMO-circuits. We here tested roller pumps as rescue pump for ECMO-establishment. Methods: We set up in vitro circuits on roller pumps from C5 heart-lung-machine with 5 l/minutes flow. In two series, we placed either PVC or silicon tubing for an ECMO circuit into the roller pump. We assessed the mechanical stress on the tubing (aiming to run the pump for at least 1 week), measured the temperature increase generated by the friction and assessed flow characteristics and its measurement in simulated situations resembling tube kinking and suction. Results: The roller pumps led to expected and unexpected adverse events. PVC tubing burst between 36 and 78 hours, while silicon tubing lasted for at least 7 days. At 7 days, the silicone tubing showed significant signs of roller pump wear visible on the outside. The inside, however, was free of surface irregularities. Using these tubings in a roller pump led to a remarkable increase in circuit temperature (PVC: +12.0°C, silicone +2.9°C). Kinking or suction on the device caused the expected dramatic flow reduction (as assessed by direct measurement) while the roller pump display continued to show the preset flow. The roller pump is therefore not able to reliably determine the true flow rate. Conclusion: Roller pumps with silicone tubing but not PVC tubing may be used for running ECMO circuits. Silicone tubing may endure the roller pump shear forces for up to 1 week. Thus, repeated tubing repositioning may be a solution. Circuit heating and substantial limitations in flow detection should increase attention if clinical use in situations of crisis is considered.

Waveform Shape Analysis: Extraction of Physiologically Relevant Information from Doppler Recordings

1994 ◽  
Vol 86 (5) ◽  
pp. 557-565 ◽  
Author(s):  
Margaret M. Ramsay ◽  
Fiona Broughton Pipkin ◽  
Peter C. Rubin ◽  
Robert Skidmore
Keyword(s):  
Laplace Transform ◽  
Pulsatility Index ◽  
Flow Characteristics ◽  
Resistance Index ◽  
Relevant Information ◽  
Peripheral Circulation ◽  
Valsalva Manoeuvre ◽  
Flow Conditions ◽  
Physiological Relevance ◽  
Healthy Female

1. Doppler recordings were made from the brachial artery of healthy female subjects during a series of manoeuvres which altered the pressure—flow characteristics of the vessel. 2. Changes were induced in the peripheral circulation of the forearm by the application of heat or icepacks. A sphygmomanometer cuff was used to create graded occlusion of the vessel above and below the point of measurement. Recordings were also made whilst the subjects performed a standardized Valsalva manoeuvre. 3. The Doppler recordings were analysed both with the standard waveform indices (systolic/diastolic ratio, pulsatility index and resistance index) and by the method of Laplace transform analysis. 4. The waveform parameters obtained by Laplace transform analysis distinguished the different changes in flow conditions; they thus had direct physiological relevance, unlike the standard waveform indices.

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

scholarly journals 3D Numerical Study of the Flow Properties in a Double-Spur Dikes Field during a Flood Process

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1574 ◽  
Author(s):  
Xun Han ◽  
Pengzhi Lin
Keyword(s):  
Water Surface ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Field Measurements ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
River Bed ◽  
Hydrodynamic Evolution ◽  
Spur Dikes ◽  
Potential Damage

A 3D numerical model is developed to study the flow characteristics of a double-spur dikes field on Yangtze River during a flood process, which was presented by the variation of the flow condition. The model is based on Navier–Stokes (NS) equations, the porous medium method (PMM) is employed to treat the solid structures including the river bed surface, the volume of fluid (VOF) method is applied to track the motion of the water surface during the flood process, and large eddy simulation (LES) is adopted to capture the turbulence transport and dissipation. Using this model, the target reach’s flow field before the construction of double-spur dikes is simulated first, while the numerical results are compared to the field measurements on flow velocity and water surface level, and fairly good agreements are shown. Then, the model is applied to reproduce the hydrodynamic evolution during a flood process after double-spur dikes’ constructions, while the detailed 3D flow fields are obtained under some certain states with different submergence rates of the spur dikes; finally, the potential damage positions around these spur dikes are analyzed accordingly.

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