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15 results on '"Rezaei, Bahram"'

1. Shear Stress Distribution Prediction in Symmetric Compound Channels Using Data Mining and Machine Learning Models

Author

Khozani, Zohreh Sheikh, Khosravi, Khabat, Torabi, Mohammadamin, Mosavi, Amir, Rezaei, Bahram, and Rabczuk, Timon

Subjects
Physics - Fluid Dynamics, Computer Science - Machine Learning, Statistics - Machine Learning, 68T05
Abstract

Shear stress distribution prediction in open channels is of utmost importance in hydraulic structural engineering as it directly affects the design of stable channels. In this study, at first, a series of experimental tests were conducted to assess the shear stress distribution in prismatic compound channels. The shear stress values around the whole wetted perimeter were measured in the compound channel with different floodplain widths also in different flow depths in subcritical and supercritical conditions. A set of, data mining and machine learning models including Random Forest (RF), M5P, Random Committee (RC), KStar and Additive Regression Model (AR) implemented on attained data to predict the shear stress distribution in the compound channel. Results indicated among these five models, RF method indicated the most precise results with the highest R2 value of 0.9. Finally, the most powerful data mining method which studied in this research (RF) compared with two well-known analytical models of Shiono and Knight Method (SKM) and Shannon method to acquire the proposed model functioning in predicting the shear stress distribution. The results showed that the RF model has the best prediction performance compared to SKM and Shannon models., Comment: 29 pages, 6 figures

Published
2019

2. Flow characteristics in compound channels with skewed and inclined floodplains.

Author

Dolatimahtaj, Mostafa and Rezaei, Bahram

Subjects
SHEARING force, FLOODPLAINS, FLOW velocity, FLUMES, STREAMFLOW
Abstract

Understanding the flow characteristics of rivers in both their inbank and overbank flow conditions is an important task for engineers. So far, many studies have been carried out in compound channels with prismatic and non-prismatic floodplains. However, we still don't understand the effect of the floodplain's side slope on the flow field in compound channels. This paper presents the results of experiments on compound channels with skewed and inclined floodplains (lateral slope of 0.075). Velocity and boundary shear stress were measured at various experimental sections for different relative depths and two skew angles of 3.81º and 11.31º. Using the measured data, the secondary currents pattern, the apparent shear forces at the vertical interface between the main channel and floodplains, and the discharge distribution in the main channel and the floodplains along the flume have been investigated. The results of the experiments were then compared to the experimental data of the skewed compound channel with flat floodplains. The research shows that due to lateral flow and momentum exchange between flume subsections, the flow velocity, bed shear stress, and percentage discharge on the diverging floodplain are greater than those on the converging floodplain with the same cross-sectional geometry. [ABSTRACT FROM AUTHOR]

Published
2025
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4. Overbank flow in compound channels with prismatic and non-prismatic floodplains

Author

Rezaei, Bahram

Subjects
627
Abstract

Two sets of experiments have been undertaken in compound channels with prismatic and nonprismatic floodplains with different floodplain widths and convergence angles in order to investigate flow behaviour in two-stage channels. Measurements were made of water surface profile, depth-averaged velocity, boundary shear stress distributions and velocity distributions and the results are presented in graphical and tabulated form. Empirical equations have been derived from each type of compound channel, allowing predictions to be made concerning the resistance parameters, n and f, the discharge, Q, the proportion of total flow in sub-areas, %Qj, the evolution of flow in the main channel and on the floodplain along the converging part of the flume, the boundary shear forces, SFj, and the apparent shear forces at a vertical and horizontal interface between the main channel and the floodplain, for a given stage, H. The percentage of flow in the main channel and on the floodplain, as well as the percentage of the boundary shear forces carried by each element in different sections of the compound channel with non-prismatic floodplains, were then compared with the prismatic floodplain cases with the same geometry. The results of these two sets of experiments indicate that they follow the same pattern, although there are some differences due to the effects of backwater and convergence in the flume. The apparent shear forces on a vertical interface, ASFv, are however remarkably different. Based on momentum balance, an analytical approach was developed to estimate the water surface profile in non-prismatic compound channels with different convergence angles, 9. The calculated water surface profiles compared well with the measured ones. It is shown that the Shiono and Knight Method (SKM) predicted lateral distributions of the depth-averaged velocity and boundary shear stress well, especially for prismatic compound channels with wide floodplains. Furthermore, there is a good agreement between the measured and predicted distributions in non-prismatic compound channels, provided the energy slope, Se,is used instead of the bed slope, So. The experimental results were then also used to calibrate the two parameter, ",t, and ",g, in the Exchange Discharge Model (EDM). This revealed that the calibration of the turbulent exchange parameter, wt strongly depends on the Manning's roughness coefficient. In term of compound channels with non-prismatic floodplains it is also shown that the EDM always overestimates the flow discharge for a specific stage.

Published
2006

7. Prediction of Percentage Discharge Distribution in Non-Prismatic Compound Channels with Skewed Floodplains.

Author

Mahtaj, Mostafa Dolati and Rezaei, Bahram

Subjects
FLOODPLAINS, HYDRAULIC engineering, HYDRAULIC engineers, REGRESSION analysis, COEFFICIENTS (Statistics)
Abstract

In rivers with non-prismatic compound cross-sections, due to the change in cross-section along the channel, mass exchange between the main channel and floodplains. Therefore, discharge distribution in non-prismatic compound channels is an important task for river and hydraulic engineers. In this paper, some results of experiments performed in non-prismatic compound channels with skewed and inclined floodplains have been explained. Two skew angles of 3.81o and 11.31o and three discharges were investigated. The effects of relative depth and relative distance on percentage discharge distribution in each sub-section of the skewed compound channels are presented. The experimental results show that the percentage discharge in each sub-section relies upon the parameters like relative depth, relative distance, skew angle, and floodplain side slope. By using the experimental results, multivariable regression models have been developed to estimate the percentage of discharge in the main channel and on the floodplains. Investigations indicate that the regression models presented in this research, in the validation range, can predict the percentage of discharge in each sub-section of the skewed compound channel fairy well. So that for the results used in this research, the coefficient of determination (R2) for predicting discharge regression model in the main channel is 0.96, on the diverging floodplain is 0.92, and on the converging floodplain is 0.91. Also, the mean absolute percentage errors (MAPE) between the calculated and measured value of percentage discharge in the main channel, on the diverging floodplain, and the converging floodplain are equal to 1.47%, 14.29%, and 21.7%, respectively. [ABSTRACT FROM AUTHOR]

Published
2022
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