scholarly journals Modeling open channel flow resistance with dune bedform via heuristic and nonlinear approaches

2018 ◽  
Vol 20 (2) ◽  
pp. 356-375 ◽  
Author(s):  
Kiyoumars Roushangar ◽  
Mohammad Taghi Alami ◽  
Seyed Mahdi Saghebian
Keyword(s):  
Flow Resistance ◽  
Accurate Determination ◽  
Flow Characteristics ◽  
Roughness Coefficient ◽  
Data Series ◽  
Shear Stresses ◽  
Alluvial Channels ◽  
Mean Velocity ◽  
Hydraulic Roughness ◽  
Manning’S Coefficient

Abstract Flow resistance in open channels with dune bedform is a substantial issue due to the influence of dunes on the hydraulic roughness, which can affect the performance of hydraulic constructions. There are a number of nonlinear approaches that have been developed to predict the roughness coefficient in alluvial channels, such as developed equations based on the mean velocity or shear stresses. However, due to the multitude of factors influencing roughness, establishing an accurate determination of the roughness coefficient is difficult. This study applies gene expression programing (GEP) and nonlinear approaches to predict the Manning's coefficient in dune bedform channels. Four different experimental data series were used for modeling. In order to develop the models, three scenarios with different input combinations were considered: scenario 1 considers only flow characteristics, scenario 2 considers flow and bedform characteristics, and scenario 3 considers flow and sediment characteristics. The results proved that GEP is capable of predicting the Manning's coefficient. It was found that for estimation of the roughness coefficient in dune bedform channels, scenario 3 performed more successfully than others. Sensitivity analysis showed that the Reynolds number plays a key role in the modeling process. Comparisons between GEP models and existing equations indicated that GEP models yield better results.

Analysis of Flow Resistance Inside Microchannels With Different Inlet Configurations Using Micro-PIV System

2003 ◽  
Author(s):  
Sang-Joon Lee ◽  
Guk-Bae Kim
Keyword(s):  
Flow Resistance ◽  
Reduction Rate ◽  
Flow Characteristics ◽  
Entrance Region ◽  
Curvature Radius ◽  
Microfluidic Chips ◽  
Mean Velocity ◽  
Dimethyl Siloxane ◽  
Micro Piv ◽  
Macro Scale

Most microfluidic chips consist of several microchannels inside. In order to design microfluidic chips efficiently, it is important to predict the flow passage and to understand the flow characteristics on the chip. In this study, the flow structure inside microchannels has been investigated using a micro-PIV system. We focused on the flow resistance with respect to the inlet configuration of microchannels. The microchannels made of poly-dimethyl-siloxane (PDMS) material were fabricated by a micro-molding technique using SU-8 (photoresist) master. The width (w) and depth of the microchannels were fixed as 100 μm and 58 μm, respectively. Six different inlet configurations with curvature radii in the ranges from r = 0.2w to 1.5w were tested in this study. As a result, with increasing the curvature radius of the inlet corner, the streamwise mean velocity develops slowly in the entrance region, but the fully developed velocity at further downstream is increased. When the curvature radius is larger than r = 0.6w, the reduction rate of flow resistance is not so significant. For the microchannels with r = 0.6w, 0.8w and 1.0w the downstream mean velocity at channel center has nearly the same value of about 276 mm/sec, 10.5% larger than that of r = 0.2w. The simple rounding of microchannel inlet corner reduces flow resistance effectively by smoothing the incoming flow. The length of entrance region is much smaller than that of macro-scale channel.

Wind Tunnel Tests on Flow Characteristics of the KRISO 3,600 TEU Containership and 300K VLCC Double-Deck Ship Models

2003 ◽  
Vol 47 (01) ◽  
pp. 24-38 ◽  
Author(s):  
Sang-Joon Lee ◽  
Hak-Rok Kim ◽  
Wu-Joan Kim ◽  
Suak-Ho Van
Keyword(s):  
Wind Tunnel ◽  
Flow Characteristics ◽  
Shear Stresses ◽  
Spatial Distributions ◽  
Wake Region ◽  
Turbulence Statistics ◽  
Near Wake ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Longitudinal Vortices

The flow characteristics in the stern and near-wake region of two ship models, the Korea Research Institute of Ships and Ocean Engineering (KRISO) 3,600 TEU containership (KCS) and the KRISO 300K very large crude oil carrier (VLCC) (KVLCC), were investigated experimentally. The double-deck ship models were installed in a subsonic wind tunnel. The freestream velocity was fixed at Uo = 25 m/s, and the corresponding Reynolds numbers based on the model length (Lpp) were about 3.3x 106 and 4.6x 106for the KCS and KVLCC models, respectively. The spatial distributions of mean velocity components and turbulence statistics, including turbulence intensities, Reynolds shear stresses, and turbulent kinetic energy, were measured using a hot-wire anemometer. For both ship models, the stern flow and near-wake show very complicated three-dimensional flow patterns. The longitudinal vortices formed in the stern region dominantly influence the flow structure in the near-wake region. In the region of main longitudinal vortices, the mean velocity deficits and all turbulence statistics have large values, compared with the surrounding flow. As the flow moves downstream, the turbulence statistics increase and have maximum values at the after-perpendicular (AP) plane and then decrease gradually due to the expansion of the shear layer. For the KVLCC model, the spatial distributions of mean velocity components and turbulence intensities behind the propeller plane clearly show hook-shaped contours. These experimental results, especially the turbulence statistics, can be used not only to understand the flows around modern practical hull forms but also to validate the computational fluid dynamics codes and turbulence models. The complete experimental data set is available on the website (http://www.postech.ac.kr/me/efml/data).

Re-Circulating Flows Associated with Two-Dimensional Steps

1980 ◽  
Vol 31 (3) ◽  
pp. 151-172 ◽  
Author(s):  
W.D. Moss ◽  
S. Baker
Keyword(s):  
Bluff Body ◽  
Accurate Determination ◽  
Mixing Layer ◽  
Separated Flow ◽  
Shear Layers ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Mean Velocity ◽  
High Turbulence

SummaryThis paper describes measurements made in the regions of separated flow associated with three simple sharpedged two-dimensional geometries, a rear-facing step, a front-facing step and a rectangular block. The use of the pulsed-wire anemometer made possible the measurement of the three components of mean velocity and turbulence; earlier techniques, such as the hot-wire anemometer, were not well suited to the accurate determination of these quantities either in regions of continually reversing flows such as the re-circulatory zone or in regions of very high turbulence such as the shear layers bounding these zones. Supplementary measurements of surface pressure and shear stresses are also presented and comparison is made between these shear layers and the plane mixing layer. The work forms the first part of an extended programme for the investigation of bluff body flows but its principal immediate value will probably help in providing data with which to test the validity of mathematical models of turbulence as applied to re-circulating flows.

scholarly journals Measuring the turbulent characteristics in an open channel using the PIV method

2013 ◽  
Vol 14 (3) ◽  
pp. 378-385
Keyword(s):  
Open Channel ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Vegetation Height ◽  
Hydraulic Behaviour ◽  
Turbulent Characteristics ◽  
Wide Range ◽  
Vegetation Region

Investigation of open channel flows is very important for a wide range of applications, including restoration and enhancement of river aquatic systems. As a result, the scientific community has focused on providing further insights on the flow characteristics in vegetated channels. Vegetation may be submerged or emerged, rigid or flexible with high or low density. For rigid vegetation, the hydraulic behaviour of the channel is similar to the behaviour of a channel with macro-roughness which could be caused by the presence of geometrical elements (e.g. cylinders, cubes). For flexible vegetation, both the flexibility of the vegetation and the hydrodynamic of the flow contribute to the generation of several formations such as erect, gently swaying, and prone. In this study, the characteristics of turbulent flow in an open channel were studied experimentally using Particle Image Velocimetry (PIV). This method assumes that the particles of a fluid faithfully follow the flow dynamics, hence the motion of these seeding particles are used to calculate velocity information of the flow. The experiments were conducted for both impermeable and permeable beds in a channel of 6.5m length, 7.5 cm width and 25 cm height. Two grass-like vegetation types of different height (2 and 6 cm) were used to represent permeable beds. These conditions are typical of flows encountered in sediment transport problems. Hydraulic characteristics such as distributions of velocities, turbulent intensities and Reynolds stress are investigated at a fine resolution using the PIV. Velocity is measured above the vegetation at different heights. Results show that velocity over the vegetation region is a function of the vegetation height and the total flow depth; velocity decreases as the vegetation height increases. In addition, we show that velocities above the vegetation region are much lower than velocities above an impermeable bed. This is due to the turbulent shear stresses and the existence of turbulence in the vegetation region, which reduce the mean velocity above the vegetation region. In addition, results show a region of zero velocity; between 3 and 6 cm and 1 and 2 cm for a 6 cm and 2 cm vegetation. This result shows that 50% of the vegetation behaves like an impermeable bed.

scholarly journals Flow Resistance Equation in Sand-bed Rivers and Its Practical Application in the Yellow River

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 727
Author(s):  
Rongrong Cai ◽  
Hongwu Zhang ◽  
Yu Zhang ◽  
Luohao Zhang ◽  
Hai Huang
Keyword(s):  
Flow Resistance ◽  
Yellow River ◽  
Flow Characteristics ◽  
Viscous Sublayer ◽  
Channel Width ◽  
Roughness Coefficient ◽  
Influence Coefficient ◽  
Wall Region ◽  
River Training ◽  
Resistance Equation

To fully reflect the effect of the flow characteristics, sidewall conditions and sediment concentrations on the bed roughness of sand-bed rivers, this study established a new flow resistance equation by introducing a comprehensive influence coefficient presented via a combination of power-function forms of the relative flow velocity, von Karman constant of sediment-laden flows and the ratio of particle size to viscous sublayer thickness. The comprehensive influence coefficient accordingly acts as a synthesized factor representing the combined effects of the flow intensity, bed material movement, energy consumption condition, and relative friction condition in the near-wall region of sediment-laden flows. Based on the field data from sediment-laden flows under scenarios of both high and low sediment concentrations, the performance of the proposed equation was validated to achieve the best accuracy in the calculation of Manning’s roughness coefficient compared with that of several previously presented flow resistance equations. Furthermore, the proposed flow resistance equation was adopted to quantify the stable channel width of the Lower Yellow River (LYR), i.e., the optimum main channel width for sediment transportation in the typical wandering reach of the LYR. The calculated stable channel width is consistent with the current river training width of the LYR, indicating that the proposed equation has great potential as a theoretical tool that can be used to support the determination of the river training strategy for the LYR.

scholarly journals Assessing Machine Learning versus a Mathematical Model to Estimate the Transverse Shear Stress Distribution in a Rectangular Channel

Mathematics ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 596
Author(s):  
Babak Lashkar-Ara ◽  
Niloofar Kalantari ◽  
Zohreh Sheikh Khozani ◽  
Amir Mosavi
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Fuzzy Inference ◽  
Rectangular Channel ◽  
Tsallis Entropy ◽  
Shear Stress Distribution ◽  
Data Series ◽  
Shear Stresses ◽  
Inference System ◽  
Aspect Ratios

One of the most important subjects of hydraulic engineering is the reliable estimation of the transverse distribution in the rectangular channel of bed and wall shear stresses. This study makes use of the Tsallis entropy, genetic programming (GP) and adaptive neuro-fuzzy inference system (ANFIS) methods to assess the shear stress distribution (SSD) in the rectangular channel. To evaluate the results of the Tsallis entropy, GP and ANFIS models, laboratory observations were used in which shear stress was measured using an optimized Preston tube. This is then used to measure the SSD in various aspect ratios in the rectangular channel. To investigate the shear stress percentage, 10 data series with a total of 112 different data for were used. The results of the sensitivity analysis show that the most influential parameter for the SSD in smooth rectangular channel is the dimensionless parameter B/H, Where the transverse coordinate is B, and the flow depth is H. With the parameters (b/B), (B/H) for the bed and (z/H), (B/H) for the wall as inputs, the modeling of the GP was better than the other one. Based on the analysis, it can be concluded that the use of GP and ANFIS algorithms is more effective in estimating shear stress in smooth rectangular channels than the Tsallis entropy-based equations.

scholarly journals New Equation for Predicting Pipe Friction Coefficients Using the Statistical Based Entropy Concepts

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 611
Author(s):  
Yeon-Woong Choe ◽  
Sang-Bo Sim ◽  
Yeon-Moon Choo
Keyword(s):  
Friction Coefficient ◽  
Accurate Determination ◽  
Mean Velocity ◽  
Friction Coefficients ◽  
Flow Discharge ◽  
Comparison Results ◽  
Flow Loss ◽  
Key Variables ◽  
New Equation

In general, this new equation is significant for designing and operating a pipeline to predict flow discharge. In order to predict the flow discharge, accurate determination of the flow loss due to pipe friction is very important. However, existing pipe friction coefficient equations have difficulties in obtaining key variables or those only applicable to pipes with specific conditions. Thus, this study develops a new equation for predicting pipe friction coefficients using statistically based entropy concepts, which are currently being used in various fields. The parameters in the proposed equation can be easily obtained and are easy to estimate. Existing formulas for calculating pipe friction coefficient requires the friction head loss and Reynolds number. Unlike existing formulas, the proposed equation only requires pipe specifications, entropy value and average velocity. The developed equation can predict the friction coefficient by using the well-known entropy, the mean velocity and the pipe specifications. The comparison results with the Nikuradse’s experimental data show that the R2 and RMSE values were 0.998 and 0.000366 in smooth pipe, and 0.979 to 0.994 or 0.000399 to 0.000436 in rough pipe, and the discrepancy ratio analysis results show that the accuracy of both results in smooth and rough pipes is very close to zero. The proposed equation will enable the easier estimation of flow rates.

scholarly journals Morphology Development and Flow Characteristics during High Moisture Extrusion of a Plant-Based Meat Analogue

Foods ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1753
Author(s):  
Patrick Wittek ◽  
Felix Ellwanger ◽  
Heike P. Karbstein ◽  
M. Azad Emin
Keyword(s):  
Transition Zone ◽  
Flow Characteristics ◽  
Phase System ◽  
Shear Stresses ◽  
High Moisture ◽  
Tensile Stresses ◽  
Morphology Development ◽  
A Minor ◽  
Multi Phase ◽  
High Moisture Extrusion

Plant-based meat analogues that mimic the characteristic structure and texture of meat are becoming increasingly popular. They can be produced by means of high moisture extrusion (HME), in which protein-rich raw materials are subjected to thermomechanical stresses in the extruder at high water content (>40%) and then forced through a cooling die. The cooling die, or generally the die section, is known to have a large influence on the products’ anisotropic structures, which are determined by the morphology of the underlying multi-phase system. However, the morphology development in the process and its relationship with the flow characteristics are not yet well understood and, therefore, investigated in this work. The results show that the underlying multi-phase system is already present in the screw section of the extruder. The morphology development mainly takes place in the tapered transition zone and the non-cooled zone, while the cooled zone only has a minor influence. The cross-sectional contraction and the cooling generate elongational flows and tensile stresses in the die section, whereas the highest tensile stresses are generated in the transition zone and are assumed to be the main factor for structure formation. Cooling also has an influence on the velocity gradients and, therefore, the shear stresses; the highest shear stresses are generated towards the die exit. The results further show that morphology development in the die section is mainly governed by deformation and orientation, while the breakup of phases appears to play a minor role. The size of the dispersed phase, i.e., size of individual particles, is presumably determined in the screw section and then stays the same over the die length. Overall, this study reveals that morphology development and flow characteristics need to be understood and controlled for a successful product design in HME, which, in turn, could be achieved by a targeted design of the extruders die section.

Experimental Study on Hydraulic Roughness of Submerged Grass in Ecological Riverbank

2013 ◽  
Vol 838-841 ◽  
pp. 1743-1748
Author(s):  
Dian Guang Ma ◽  
Chun Xin Zhong ◽  
Wu Ning ◽  
Qing Ye ◽  
Sheng Zhu
Keyword(s):  
Flow Velocity ◽  
Roughness Coefficient ◽  
Theoretic Analysis ◽  
Mean Flow ◽  
Normal Range ◽  
Obvious Effect ◽  
Hydraulic Roughness ◽  
Natural Turf ◽  
Scouring Process ◽  
The Mean

A model experiment about the hydraulic roughness of natural turf used in riverbank was carried out in flume. To examine the rationality of experimental design, the hydraulic roughness coefficient of plexiglass-flume was tested firstly. The result was 0.0085, which is quite normal. Then the tested hydraulic roughness caused by vegetation ranges from 0.020 to 0.090 for the chosen plants, which is also acceptable. Furthermore, the tested incipient velocities of krasnozem, and paddysoil had the range of 0.55~0.65m·s-1 and 1.0~1.1m·s-1, respectively. All these experimental results are in normal range, which means that the design of this experimental is rational. Experimental research illustrate that, the roughness coefficient of plant reduces with the increasing of flow velocity. When the mean flow velocity is over 3m·s-1, Mannings n values vary between 0.025 and 0.035. This phenomenon is accord with the theoretic analysis. During the scouring process, not only the flow velocity, but also the flow duration has an obvious effect on the coarseness of vegetative bed.

scholarly journals Overland Flow Resistance Law under Sparse Stem Vegetation Coverage

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1657
Author(s):  
Jingzhou Zhang ◽  
Shengtang Zhang ◽  
Si Chen ◽  
Ming Liu ◽  
Xuefeng Xu ◽  
...  
Keyword(s):  
Flow Resistance ◽  
Overland Flow ◽  
Vegetation Coverage ◽  
Dominant Factor ◽  
Roughness Coefficient ◽  
Hydraulic Parameters ◽  
Slope Condition ◽  
Manning Roughness ◽  
The Relationship ◽  
Manning Roughness Coefficient

To explore the characteristics of overland flow resistance under the condition of sparse vegetative stem coverage and improve the basic theoretical research of overland flow, the resistance characteristics of overland flow were systematically investigated under four slope gradients (S), seven flow discharges (Q), and six degrees of vegetation coverage (Cr). The results show that the Manning roughness coefficient (n) changes with the ratio of water depth to vegetation height (h/hv) while the Reynolds number (Re), Froude number (Fr), and slope (S) are closely related to vegetation coverage. Meanwhile, h/hv, Re, and Cr have strong positive correlations with n, while Fr and S have strong negative correlations with n. Through data regression analysis, a power function relationship between n and hydraulic parameters was observed and sensitivity analysis was performed. It was concluded that the relationship between n and h/hv, Re, Cr, Q, and S shows the same law; in particular, for sparse stem vegetation coverage, Cr is the dominant factor affecting overland flow resistance under zero slope condition, while Cr is no longer the first dominant factor affecting overland flow resistance under non-zero slope condition. In the relationship between n and Fr, Cr has the least effect on overland flow resistance. This indicates that when Manning roughness coefficient is correlated with different hydraulic parameters, the same vegetation coverage has different effects on overland flow resistance. Therefore, it is necessary to study overland flow resistance under the condition of sparse stalk vegetation coverage.

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