Time of Concentration (TC) is one of the most frequently used time parameters in many hydrologica... more Time of Concentration (TC) is one of the most frequently used time parameters in many hydrological studies. A good estimation of TC value results in a more precise design of expensive hydraulic structures, as well as a better estimation of ood discharge. There are the three available approaches to determine TC: physical, empirical, and graphical methods. Among these, graphical method is a widely accepted and popular among researchers for estimating TC. It is also considered as benchmark in TC studies. However, this method faces problems due to the lack of recorded data in many catchments. In this study, two-dimensional (2D) hydraulic simulation is studied and suggested as a novel technique for calculation of TC. The required input for 2D simulation can be obtained by using free satellite data. Some empirical formulas were also considered for calculating TC as well. The graphical method was used as a benchmark to evaluate the outputs of hydraulic simulation, and empirical formulas. To do this, four different watersheds were considered, with 28 rainfall-runoff events. In hydraulic simulation, TC was calculated as the time taken by a water parcel to travel from the upstream (headwater) to the downstream (outlet) of a watershed. The TC values obtained from the hydraulic simulation, and empirical formulas were compared with graphical method. It was observed that the maximum difference between the graphical method and the 2D simulation was less than 10% in all watersheds. Therefore, hydraulic simulation is a reliable method for calculating TC, especially in ungauged catchments where graphical method is not applicable.
The causes of many bridge failures have been reported to be local scour around abutments. This st... more The causes of many bridge failures have been reported to be local scour around abutments. This study examines roughening elements as devices with which to intercept the downflow responsible for the formation of the principal vortex, which is what triggers local scour around abutments. Two vertical wall abutments with different widths were examined under four different hydraulic conditions in a clear-water regime. Elements with different thicknesses (t) and protrusions (P) with the same dimensions, (P = t = 0.05 L, 0.1 L, 0.2 L, and 0.3 L, where L is the length of the abutment) and with varying depths of installation (Z) were considered. Elements were installed in two positions: between the sediment surface and water elevation and buried within the sediment. To determine the optimum depth of installation, one element was first installed on the sediment surface, and the number of elements was increased in each subsequent test. The results show that installing elements between water su...
A laboratory study on paddle type wave energy converter for transferring seawater using wave energy
Using wave energy for desalination is recently noticed by researchers and authorities. This is kn... more Using wave energy for desalination is recently noticed by researchers and authorities. This is known in industry as wave to water and is especially vital for regions/islands where have access to seas and oceans but suffer from shortage of drinking water. Some devices are developed to perform this operation in industry sector as well as academic studies performed in this regard, yet study on geometrical optimization of these devices is required. Studies aiming to optimize the wave energy convertor (WEC) geometry are expensive in field. As a result, investigations are divided into numerical and experimental studies in which the former requires validation by observed data. In this paper, a preliminary experimental study on parameters affecting the performance of a paddle type WEC, such as paddle width, water depth, coast slope, and wave frequency period on the performance of the converter is conducted by running laboratory tests. This kind of WEC is used in industry. Analysis to scale ...
Time of concentration (TC) is a parameter in runoff estimation, used to study and design differen... more Time of concentration (TC) is a parameter in runoff estimation, used to study and design different types of projects in watersheds. Any error in TC calculation leads to an inaccurate estimation of the design flow, which can lead to over-sizing or under-sizing of designed facilities that can have great economic and environmental consequences. Therefore, choosing the correct method to estimate TC is of great importance. Due to the diversity of estimation methods in the literature, the obtained TC values are different. This study aims to present a new method to calculate TC, based on its main concept, i.e., the time required for a water parcel to reach its outlet from the farthest hydrological point of a watershed. A two-dimensional hydraulic simulation was used to model the water parcel travel. A watershed was selected as a case study, and its time of concentration was determined by salt solution tracing. The field measurement results were used for calibration of the numerical simulat...
Scour is one of the main causes of hydraulic structural failures. The present experimental study ... more Scour is one of the main causes of hydraulic structural failures. The present experimental study examines the use of riprap, submerged vanes, and a combination of these for scour reduction around vertical walls and spill-through abutments under clear-water conditions. Specifically, the influence of placing riprap stones with different apron shapes (geometry) and/or a group of submerged vanes of constant height and length on abutment scour was examined. The main aim is to propose the optimum apron geometry and placement of submerged vanes to (1) reduce edge failure at vertical walls and spill-through abutments; and (2) prevent shear failure at the spill-through abutment (no shear failure is observed around the vertical wall abutment). The results show that using ripraps for scour protection is more effective than submerged vanes. However, the highest reduction in scour depth was achieved when a combination of riprap and submerged vanes was used together. This arrangement can reduce t...
معرفی شبیه سازی هیدرولیکی دوبعدی جریان به عنوان روشی جهت تخمین زمان تمرکز
زمان تمرکز پارامتری اساسی در برآورد سیلاب جهت طراحی انواع سازه های هیدرولیکی است. لذا انتخاب روش ... more زمان تمرکز پارامتری اساسی در برآورد سیلاب جهت طراحی انواع سازه های هیدرولیکی است. لذا انتخاب روش صحیح برآورد زمان تمرکز از اهمیت خاصی برخوردار است. هدف از این تحقیق ارائه روشی نوین جهت محاسبه زمان تمرکز بر اساس مفهوم اصلی آن یعنی مدت زمان لازم جهت حرکت آب از دورترین نقطه هیدرولوژیکی حوضه تا خروجی آن میباشد. بدین منظور مدلسازی حرکت آب به وسیله شبیهسازی هیدرولیکی دوبعدی صورت گرفته است. حوضه آبریز علیآباد در استان فارس به عنوان مطالعه موردی انتخاب گردیده و زمان تمرکز آن به وسیله روش ردیاب محلول نمک تعیین گردیده است. نتایج اندازهگیری صحرایی جهت صحتسنجی شبیهسازی عددی مورد استفاده قرار گرفته است. غیر از شبیهسازی عددی، مقادیر زمان تمرکز با استفاده از 48 معادله تجربی محاسبه گردید از میان روشهای تجربی محاسبه زمان تمرکز، حداکثر خطای بدست آمده بیش از سیصد درصد و حداقل خطای بدست آمده معادل 7/6 درصد میباشد. نتایج شبیهسازی عددی نیز بسته به تعریف و مقادیر مختلف پارسل آب بین 3 تا 27 درصد خطا داشتهاند که در مقایسه با روشهای تجربی نتایج بسیار بهتری میباشد. به طور کلی نتایج نشان میدهد ک...
A numerical model called MIKE21 was evaluated for simulation of dam and dike breaks. In recent ye... more A numerical model called MIKE21 was evaluated for simulation of dam and dike breaks. In recent years in Iran and other parts of the world some dike-breaches have been reported. Application of two-dimensional models in simulation of dike-breaches is inevitable, because of the nature of the flood propagation after the break. However, in Iran, there are very few twodimensional models used in river and floodplain issues. Hence, the performance of MIKE21 as a numerical model for simulation of dike break was investigated in this research. MIKE21 was originally developed for flow simulation in coastal areas, estuaries and seas. MIKE21's performance in simulation of dam and dike-break was studied via comparison with analytical solutions, other numerical approaches and available experimental data. Fair agreement has been observed, but care should be taken when modeling shock waves with MIKE21. The study was finally extended to a real case study. Some dike-break scenarios were considered in the Helleh River, in Iran and the results are discussed and presented.
Flow separation at the upstream side of the lateral turnouts (intakes) is a critical issue causin... more Flow separation at the upstream side of the lateral turnouts (intakes) is a critical issue causing eddy currents at the turn-out entrance. It reduces the effective width of flow, turn-out capacity and efficiency. Therefore, it is essential to identify the dimensions of the separation zone and propose remedies to reduce its dimensions. Installation of 7 types of roughening elements at the turn-out entrance and 3 different bed level inverts, with 4 different discharges (total of 84 experiments) were examined in this study as a method to reduce the dimensions of the separation zone. Additionally, a 3-D Computational Fluid Dynamic (CFD) model was utilized to evaluate the flow pattern and dimensions of the separation zone. Results showed that enhancing the roughness coefficient can reduce the separation zone dimensions up to 38% while the drop implementation effect can scale down this area differently based on the roughness coefficient used. Combining both methods can reduce the separati...
We proceed the research of generalized quasigroup derivatives started in early papers of the last... more We proceed the research of generalized quasigroup derivatives started in early papers of the last co-author ([20, p. 212], [13]). For any quasigroup there exist 648 generalized derivatives. Here we study the problem about existence of units (left, right, middle) in quasigroups that are a generalized derivative of a quasigroup. There exist 1944 various cases. For every case we find a proof or a counterexample, often using Prover or Mace .
Iranian Journal of Science and Technology, Transactions of Civil Engineering, 2020
Ski-jump spillway (SJS) is one of the energy-dissipating structures, passing the flood through th... more Ski-jump spillway (SJS) is one of the energy-dissipating structures, passing the flood through the dams. In these structures, the downstream bed is scoured due to the collision of the high energy jet. It is essential to obtain information on the scourhole dimensions to enhance the safety of the dam and related structures. The machine learning and data mining methods are efficient in predicting hydraulic phenomena. In this study, the geometric properties of the scour-hole including the hole expansion (width), maximum depth of the scour and its distance from the end edge of the spillway were predicted using a model by combining the adaptive neuro-fuzzy inference system (ANFIS) and the particle swarm optimization (PSO) algorithm. The results showed that the developed ANFIS-PSO model obtained maximum scour depth with a precision of R 2 = 0.94 and RMSE = 0.565, scour hole width with precision of R 2 = 0.95 and RMSE = 1.153 and its distance from the end edge of the SJS with an accuracy of R 2 = 0.96 and RMSE = 1.809. The evaluation and comparison of the simulation results indicated the superiority of the proposed model over other methods.
The main issue of this paper is to analyze the water depth uncertainty in manholes of a main pipe... more The main issue of this paper is to analyze the water depth uncertainty in manholes of a main pipeline of urban surface drainage system. Also sensitivity analysis for subcatchment peak flood discharge is investigated. As a case study, a basin located in the center of historical city, Shiraz, in southwest of Iran is considered. SWMM model is used to simulate rainfall-runoff process and flood routing in conduits. Monte-Carlo simulation and L.H.S method is used for uncertainty analysis. The results showed that water depth coefficient of variation in manholes varies from 12% to 66% and its probability distribution has a considerable positive skewness. Subbasin areas and precipitation parameters leave the most important effect on peak flood discharge and its uncertainty.
Determining the capability of artificial intelligence in estimating energy dissipation of skimming flow regime at stepped spillways
Energy dissipation in stepped spillways is one of the primary goals of such structures. In this s... more Energy dissipation in stepped spillways is one of the primary goals of such structures. In this study, the accuracy of the Artificial Neural Network (ANN), Adaptive Fuzzy Neural Inference System based on the trained Firefly Algorithm utilized for optimization (ANFIS-FA) and the Gene Expression Programming method (GEP), in estimating the energy loss of skimming flow regime over stepped spillways was studied. Also, by performing sensitivity analysis, the importance of input parameters in predicting energy loss for each of the three mentioned methods was investigated. For this purpose, 154 series of experimental data were considered. The input parameters for each method include hydraulic jump, Froude number, Drop number, number of steps, Pseudo bottom slope and the ratio of the critical depth to the height of each step. The results show that all three methods had a higher ability to predict energy loss compared to classical methods based on conventional regression methods. The accuracy...
Introduction: Study of the flow pattern at the lateral intakes where separation occurs is a criti... more Introduction: Study of the flow pattern at the lateral intakes where separation occurs is a critical issue. The flow rate and sediment trap are highly dependent on the flow structure in this area. Flow separation occurs due to the detachment of stream lines from the channel side walls. It creates a secondary flow similar to what happens at river bends. Flow separation reduces the efficiency by decreasing the flow effective area at lateral intakes. It also creates a region with horizontal vortices where is prone to sedimentation. Hence, finding a method to reduce the separation zone dimensions is significantly important. Different techniques have been introduced in the literature such as installation of submerged vanes, deployment of different intake angles to main channel, construction of the entrance part as a part of circles with various radiuses, etc. This study examines the effects of roughness coefficient and drop implementation at the entrance of a 90-degree lateral intake on ...
Overtopping erosion of model earthen dams analysed using digital image processing method
Proceedings of the Institution of Civil Engineers - Water Management
Overtopping erosion is one of the main factors responsible for the destruction of earthen structu... more Overtopping erosion is one of the main factors responsible for the destruction of earthen structures due to floods. Considering the shortage of existing studies and the need for further research to properly understand the processes leading to breaching failure, this study investigates the effect of compaction level (dry density) on the overtopping erosion response of model compacted silty sand dams using a laboratory flume apparatus. From side-view video recordings of the homogeneous earthen dam cross-section, digital image-processing techniques are employed to track and forensically analyse and interpret the initiation and progression of the erosion edge. The results indicate that the overall pattern of initiation and development of overtopping erosion depends on the compaction level, with greater compactive effort (higher shear strength of soil) reducing its progression speed, thereby increasing the time period for the erosion edge to reach the dam's upstream crest (tB) and breaching failure. Artificial neural network and response surface methodology (RSM) approaches are investigated for estimating the experimental tB values, with the RSM-derived third-order polynomial found to produce good predictions for the three compaction levels investigated. Finally, recommendations are given for further research, including employing the experimental setup presented for investigating other types of dam failure.
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Papers by Masih Zolghadr