Numerical Investigation into Secondary Currents and Wall Shear in Trapezoidal Channels

Ansari, Kamran; Morvan, Hervé; Hargreaves, David

doi:10.1061/(asce)hy.1943-7900.0000317

Cited by 49 publications

(12 citation statements)

References 18 publications

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“…Additional work modelled the distribution of boundary stress in prismatic channels with grain roughness as a function of channel cross‐sectional geometry, secondary flow structure, and friction at the channel boundary (e.g. Knight et al ., ; Ansari et al ., ). Research suggests that partitioning of shear stress into skin and form components is necessary to estimate τ a (Thompson et al ., ; Darby et al ., ), but determination of a partitioning factor in the presence of vegetation is challenging (Nepf, ).…”

Section: Introductionmentioning

confidence: 99%

Comparison of Direct and Indirect Boundary Shear Stress Measurements along Vegetated Streambanks

Hopkinson

Wynn-Thompson

2016

River Research & Apps

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Estimates of boundary shear stress along vegetated streambanks are needed to predict streambank fluvial erosion. Because fluvial shear stress cannot be directly measured in the field, reliable estimation techniques using field instrumentation are needed. This study evaluated local bank shear stress estimation methods applicable to sloping, vegetated streambanks. Two reaches of a second order stream were modelled in a flume using a fixed-bed Froude-scale modelling technique. One reach was dominated by dense shrubs while the other reach was located in a mature forest. Direct measurements of local bank shear stress using a hot-film anemometer were compared to estimates based on velocity measurements (logarithmic method, Reynolds stresses, and turbulent kinetic energy). For channels with no or widely spaced vegetation, the velocitybased estimates underestimated the bank shear stress due to secondary flow contributions. For banks with dense vegetation, Reynolds stresses and turbulent kinetic energy estimates were statistically similar to direct measurements on average, but substantial error occurred when making point comparisons. Velocity-based estimates generally over predicted bank stress in areas of high shear at the vegetation edge and underpredicted stress within dense vegetation. Ultimately, results suggest that none of tested techniques can be broadly applied to streambanks, and flow structure is critical in selecting the appropriate estimation technique.

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Section: Introductionmentioning

confidence: 99%

Comparison of Direct and Indirect Boundary Shear Stress Measurements along Vegetated Streambanks

Hopkinson

Wynn-Thompson

2016

River Research & Apps

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“…Experimental, analytical and numerical procedures to determine the shear stress distribution in various shapes of channels have been exhaustively investigated [3][4][5][6][7][8][9][10]. Bed shear stress comprises of three terms, i.e.…”

Section: Introductionmentioning

confidence: 99%

Forecasting shear stress parameters in rectangular channels using new soft computing methods

Khozani¹,

Sheikhi²,

Mohtar³

et al. 2020

PLoS ONE

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Shear stress comprises basic information for predicting the average depth velocity and discharge in channels. With knowledge of the percentage of shear force carried by walls (% SF w ) it is possible to more accurately estimate shear stress values. The %SF w , non-dimension wall shear stress ( � t w t 0 ) and non-dimension bed shear stress ( � t b t 0 ) in smooth rectangular channels were predicted by a three methods, the Bayesian Regularized Neural Network (BRNN), the Radial Basis Function (RBF), and the Modified Structure-Radial Basis Function (MS-RBF). For this aim, eight data series of research experimental results in smooth rectangular channels were used. The results of the new method of MS-RBF were compared with those of a simple RBF and BRNN methods and the best model was selected for modeling each predicted parameters. The MS-RBF model with RMSE of 3.073, 0.0366 and 0.0354t 0 respectively, demonstrated better performance than those of the RBF and BRNN models. The results of MS-RBF model were compared with three other proposed equations by researchers for trapezoidal channels and rectangular ducts. The results showed that the MS-RBF model performance in estimating %SF w, � t w t 0 and � t b t 0 is superior than those of presented equations by researchers.

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“…Zarrati et al (2008) modelled semi-analytical equations for distribution of shear stress in straight open channels with rectangular, trapezoidal, and compound crosssectional areas. Ansari et al(2011) exhibited the utilization of computational fluid dynamics (CFD) to estimate the bed shear and wall shear stresses in trapezoidal channels. Specifically for low aspect ratio channels, the variety of inclination angle and aspect ratio conveyed significant changes to the distribution of the shear stress at the boundaries as well as in the flow structures as already shown by De Cacqueray et al (2009).…”

Section: Introductionmentioning

confidence: 99%

Prediction of depth-averaged velocity in an open channel flow

2018

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This paper presents a new methodology to predict the depth-averaged velocity along the lateral direction in an open channel flow. The novelty of this work is to determine the point velocity and estimate the discharge capacity by knowing the geometrical parameters at a section of an open channel flow. Experimental investigations have been undertaken in trapezoidal and rectangular channels to observe the variation of local velocities along both the vertical and transverse directions at testing sections. For different geometry, hydraulic and roughness conditions, the measurements are taken for several flow conditions. Multi-variable regression analysis has been adopted to develop five models to predict the point velocities in terms of non-dimensional geometric and flow parameters at any desired location. The present method is favourably compared with the analytical method of Shiono and Knight with reasonable accuracy. The performance of mathematical model is also validated with two natural river data sets. Further, statistical error analysis is carried out to know the degree of accuracy of the present models.

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Numerical Investigation into Secondary Currents and Wall Shear in Trapezoidal Channels

Cited by 49 publications

References 18 publications

Comparison of Direct and Indirect Boundary Shear Stress Measurements along Vegetated Streambanks

Comparison of Direct and Indirect Boundary Shear Stress Measurements along Vegetated Streambanks

Forecasting shear stress parameters in rectangular channels using new soft computing methods

Prediction of depth-averaged velocity in an open channel flow

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