مجله هیدرولیک
سال نوزدهم شماره 4 (Winter 2025)

Understanding the flow behavior over stepped spillways has been the subject of many previous studies. Most of the studies conducted on stepped spillways have been in skimming flow conditions and the aerated parts of the spillway. Also, many of these results have been the result of observing the flow behavior on the side of the spillway, and there is still no complete view of the flow behavior in the depth of the spillway. The present study investigates the skimming flow behavior on a short and wide stepped spillway in a non-aerated area. For this purpose, the image processing technique called particle image velocimetry )PIV( has been used to process the movement path, velocity, and behavior of the flow and analyze it in the side sections and depth of the spillway. In a few previous studies, the more detailed behavior of the skimming flow has been investigated. The results of these studies have defined some of the characteristics of two sub-regimes of the skimming flow regime. However, the behavior of the sub-regimes mentioned by the researchers was mostly described as laboratory observations. This article takes a closer look at this issue. Also, in this study, it was shown that the flow behavior in the areas above the pseudo bottom line is almost similar to different cross-sections, but in the areas under the pseudo bottom line, the flow behavior experiences significant changes, so that its effects on the velocity profiles are quite evident.

In the present study, flow characteristics in compound meandering channels under the changes of building arrangement in the floodplains were investigated using a numerical simulation. A constant sinuosity factor of 1.21 and relative flow depths (Dr) of 0.29 to 0.49 were considered to illustrate the effect of the hydraulic parameters on the variations of the velocity components. Three types of building arrangements, including structural obstacles perpendicular to the flow of the floodplain (MHT, density=18.5%), structural obstacles parallel to the flow of the floodplain (MGT, density=23.7%), and checkered structural obstacles (MFT, density=23.7%), were used. The simulated data were in good agreement with the experimental data indicating the proper ability of the numerical model in simulation. The result reveals that in the concave arc of sections CS1 and CS7 (apex sections), changing the building arrangements has a negligible effect on the change of transverse and secondary flows due to the parallelism of the main channel flow and the floodplain flow as well as the insignificant effect of the floodplain flow on the main channel. But near the convex arc, these changes are more significant. Hence in section CS4, with the increase of the Dr from 0.29 to 0.49, for cases MAT, MGT, and MHT, the maximum value of depth-averaged transverse flow strength increases by 61%, 91%, and 41%, respectively.

Predicting suspended sediment load is important for water resource management, water quality protection, erosion control, infrastructure planning, flood management, ecological conservation, pollution control, and environmental impact assessments. As a novel aspect of this study, the ANFIS-M5T model is introduced and used to predict suspended sediment loads. Our study combines the adaptive neuro-fuzzy inference system (ANFIS) and the M5T model to create a hybrid model for predicting suspended sediment load (SSL). The lagged rainfall, discharge, and SSL values were used to predict SSL. The results showed that the introduced ANFIS-M5T model performs better than other models so that it had the lowest mean absolute error (MAE: 525), the highest Nash Sutcliffe efficiency (0.98) and the lowest Percent bias (4).The ANFIS model had the second lowest MAE of 576, followed by MLP (586), RFN (682), and M5T (981). Thus the ANFIS-M5T was a reliable tool for predicting SSL. By tackling the obstacles, assessing various methods, and showcasing the ANFIS-M5T model's efficiency, our research contributes to the continuous improvement and advancement of sediment measurement techniques and tools.

This paper presents a comprehensive analytical study on the free vibration dynamics of compressible fluids within rigid-walled rectangular tanks, emphasizing the significance of fluid-structure interaction (FSI). The research derives the governing partial differential equations and boundary conditions, leading to exact solutions for two-dimensional and three-dimensional tank geometries. By employing the Rayleigh-Ritz method, the study incorporates the effects of fluid compressibility, offering a robust framework for analyzing the free vibration behavior. The paper calculates the natural frequencies through derived analytical expressions and examines the impact of varying tank dimensions (length, height, and width) on these frequencies via sensitivity analyses. Results reveal a consistent decrease in natural frequencies across all modes as the length, height, or width of the tank increases. This phenomenon is attributed to the interplay between the fluid's kinetic and potential energies, governed by the compressibility effects and the available space for wave formation within the larger tanks. The analytical approach, combined with the Rayleigh-Ritz method, provides a solid foundation for understanding FSI in engineering applications involving storage tanks and seismic-resistant structures. The study offers valuable insights into the significance of FSI considerations and highlights the importance of optimizing tank dimensions to achieve desired resonance characteristics, ensuring safe and efficient operation under various loading conditions.

Effective seepage management is crucial for the structural integrity and operational safety of earth dams. This paper presents a detailed evaluation of seepage control strategies implemented at the Shahid Yaghoubi and Maloo dams in Khorasan Razavi province, Iran. Our study utilizes hydrological and structural data to assess the impact of specific interventions. For this purpose, numerical analysis methods and commercial GeoStudio software have been used. At the Shahid Yaghoubi dam, the application of a geomembrane on the upstream face resulted in a 15% reduction in seepage flow, while the addition of a cut-off wall downstream of the dam core led to a 35% decrease in seepage. Despite these improvements, the critical hydraulic gradient in the downstream drain remained unchanged, underscoring the complexity of seepage dynamics within dam structures. Similarly, at the Maloo dam, the installation of a geomembrane and the modification of the cut-off wall height beneath the dam core achieved reductions in seepage of 6% and 25%, respectively. These results highlight the importance of tailored, site-specific adaptations in effectively managing seepage. This research provides significant insights into the optimization of seepage control measures, contributing to the development of more durable and safer earth dam structures.

Abstract To determine the free surface flow characteristics over a triangular broad crested (crump or hump) weir with different with different upstream and downstream slopes, a series of experiments were conducted in hydraulics laboratory using a 5 m long flume. The experiments were simulated by a numerical model, Flow-3D, in order to study the flow characteristics such as free surface elevation (water surface profile), Froude number, discharge coefficient and specially  the  location of critical flow state in different head ratios and ramp slopes. To investigate the hydrodynamic field over the weir, the computational results, included different turbulence models: two-equation k–ε, renormalized group (RNG), and large eddy simulation (LES).  A nested mesh with higher resolution around the weir was employed and the computatinal results showed a close agreement with experimental data. Finally, according to the results it was found that when steeper ramp slope faces upstream, the critical flow occurs exactly at the crest of the weir, while milder ramp facing upstream makes the critical flow move backward just before the crest. The critical state location showed no sensetivity to different head ratios. Moreover, discharge coefficients were calculated and it is concluded that Cd equales 0.95 and 1.30 respectively for steep slope and mild slope facing upstream. It is worth mentioning that identification the accuracy of turbulence models’ functionality among different ones offered by Flow-3D in such experiments, requires employing an additional criterion besides water surface elevation.