sabah mohamadi; Rasool Ghobadian; mahmood kashefipoor
Abstract
Introduction: It is so important for engineers to be able to predict the places in which deposition and scouring occurs. In recent two decades using the numerical models arecommon for simulating flow and sediment transport. Numerical models are valuable tools for estimating flow conditions and sediment ...
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Introduction: It is so important for engineers to be able to predict the places in which deposition and scouring occurs. In recent two decades using the numerical models arecommon for simulating flow and sediment transport. Numerical models are valuable tools for estimating flow conditions and sediment transport, and are widely applied in water resources management. For this reason, many researches focus on modeling and simulation of flow on a mobile bed in natural and alluvial rivers. Analyzer of sediment transport is one of the most complicated topics in sediment and river hydraulic.
Material and Methods: In this research a one dimensional, unsteady, hydrodynamic model is developed which can be used for simulating flow and sediment transport as semi-coupled model in river systems. In this research, the Saint- Venant’s first order partial differential hyperbolic equations are numerically solved using the Visual Basic program for river systems. In this research study a semi implicit finite difference scheme is developed to solve the Saint- Venant equations for unsteady flow. The linear equations are produced based on the partial differential equations and the staggered technique, so it is possible to employ the tri-angular matrix algorithm (TDMA) to solve them, with this algorithm the time of running model being minimum due to the least mathematical computations. The matrix form of the linearized momentum and continuity equations for a channel with upstream and downstream boundary conditions is provided. Another technique used to solve the matrix of the linear equations is Influence Line Technique (ILT). Base flow discharge and depth in each branch are introduced into the model as the initial conditions. To avoid divergence in numerical calculations, the downstream end discharge of each branch is calculated using initial flow depth and stage-discharge or Manning’s relationship. At the junctions, the upstream discharge is calculated using the algebraic sum of the discharges of the downstream branches and vice-versa; this process is continued up to the last branches at the upstream of the river system. After solving the above equations, the computed hydraulic parameters in this part are sent to the sediment transport segment. In the sediment subroutine the bed and suspended dynamic equations are discretized by finite volume method, and solved with flow equations as semi-coupled scheme. In this study the bed and suspended load rates are individually solved. The dynamic advection- dispersion equation and the bed load differential equation were applied to calculate the suspended sediment concentration and bed load transport, respectively. The Exner equation is then used to predict the changes in the river bed elevations innon-equilibrium conditions. Because ofthe nature, the sediment transport is often in non-equilibrium form, in this study, the non-equilibrium Exner equation is used to compute the bed elevations, unlike many of the known models. The use of non-equilibrium method due to the complexity of the solution and the presence of non-equilibrium parameters such as coefficients of the adaptation length and recovery is very difficult.
Results and Discussion: In non-equilibrium conditions, the numerical models have high sensitivity to two parameters including, the adaptation length coefficient for bed load and recovery coefficient for suspended load, with the sensitivity analysis for these coefficients being carried out in this research. In this study, a sensitivity analysis was performed on these parameters using developed numerical model. The developed model has this ability to simulate flow and sediment transport in complex and loop river systems. Finally, the model was simulated for the Chaudhry loop river systems. Thisriver system has 9 branches that form the loop. All channels have rectangular sections and their flows are sub-critical. The upstream boundary condition is an unsteady hydrograph with peak discharge of 250 cubic meters per seconds and base time of 8 hours. The calculated stage and discharge by the model (using Manning’s equation) was supplied to the model as a downstream boundary condition at last node. The model outputs are discharged hydrographs on different sections of each channel. The developed model has good ability to simulate the flow and sediment transport in river systems. The result showed that by selecting the adaptation length coefficient, equivalent to a multiple of 1 to 3 times the distance between cross sections, the results of the numerical model can be more realistic. Also it was concluded that empirical equation of Lin(1984) used for the recovery factor of the suspended load.
jalil javadi orte cheshme; mahmood kashefipoor
Abstract
Introduction: Nowadays, contamination of water is one of the problems that are more considered. Fecal Coliform (FC) is one of the most common indicator organisms for monitoring the quality of water. The problem that complicates the modeling of indicator organisms such as Fecal Coliform is determining ...
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Introduction: Nowadays, contamination of water is one of the problems that are more considered. Fecal Coliform (FC) is one of the most common indicator organisms for monitoring the quality of water. The problem that complicates the modeling of indicator organisms such as Fecal Coliform is determining the appropriate amount and an optimum rate of decay. It has been reported by many scientists that the decay coefficient or mortality rate is significantly affected by environmental elements. In this study, the effect of environmental parameters such as temperature, turbidity, radiation and suspended sediment concentration on the coliform decay coefficient hasbeen verified to have a dynamic and variable decay coefficient for better and reliable estimations of fecal coliform concentartion values.
Materials and Methods: Karun River is the longest and largest river in Iran. In this study, due to the accumulation of pollutants from industrial and agricultural wastes near Ahvaz city and for existence of quality measurement stations along the river, the Mollasani station to Farsiat station was selected to simulate and evaluate the hydrodynamic and quality of the river. The FASTER model has been used for modeling of the flow, sediment and water pollution. In this study, the dynamic roughness Manning coefficient has been used for more accurate simulate the flow, that had been added to the model by Mohammadi and Kashefipour. In Coliform bacteria and sediment modeling, some other dynamic parameters such as longitudinal dispersion coefficient are important and increasing or decreasing of these parameters are very significant and the accuracy of the Advection-Dispersion Equation (ADE) depends on the choice of the theoretical and/or experimental relations of these parameters. It was previously found that the Fisher equation performs the best for Karun river in modeling coliform, and this equation was therefore used in this study to calculate the dispersion coefficient. In order to investigate the effect of suspended sediment concentration on coliform decay rates, first this parameter must be modeled. In this research, the von Rijn method was used for modeling the suspended sediment load. In order to modeling the caliform, all dates of measuring were firstly determined in Zargan station; for each date the model was run for several times. For each run the decay coefficient was selected accordingly, until the predicted concentration by the model has the least difference inthe corresponding measured values. After that, the measured amount of environmental parameters such as Temperature, TUrbidity, RAdiation and also, the modeled values of suspended Sediment concentration wasdetermined for the same dates. Then, using a statistical software a relationship was developed to describe the decay coefficient as follows:
(1)
Results and Discussion: Using a statistical software, an equationfor decay coefficient was derived as follow:
(2)
Where K is decay coefficient (hr-1), T temperature (°C), TU turbidity (NTU), RA radiation(mmH2o-Vaporizeable) and Se suspended sedimentconcentration (kg/m3). Equation (2) was then added to the FASTER model, so the model was able to calculate the decay coefficient using the calculated suspended sediment at any time of simulation and this equation (dynamic decay coefficient). To be able to compare the dynamic decay coefficient and constant decay coefficient, the model was performed repeatedly for the whole calibration period and each time one constant K was given to the model. The best constant decay coefficient for the period of calibration and validation patterns was obtained to be K= 0.05 hr-1.Tables (1) and (2) show the amount of accuracy in predicting the suspended sediment concentration and coliform in both calibration and verification patterns, respectively. Table (1) shows that the FASTER model was able to estimate the suspended sediment concentration relatively accurate. Table (2) compares the effect of a constant decay coefficient versus the dynamic decay coefficient inaccurate estimation of fecal coliform concentrations.
Table 1- Comparison of the estimated error and correlation of suspended sediment
Pattern R2 a %E RMSE
Calibration 0.85 0.95 29.81 0.039
Verification 0.87 1.3 30.52 0.059
Table 2- Statistical parameters for coliform concentrations predicted and measured
Perioud k R2 a %E RMSE
Calibration Relation (2) 0.97 1.2 19 1906
0.05 0.92 2 50 4341
Verification Relation (2) 0.94 1.4 20 3860
0.05 0.77 1.5 44 7384
Conclusions: Comparison of the predicted fecal coliform concentrations with the corresponding measured values in the calibration and verification periodsshowed that the error estimate improved respectively about 31% and 24% when the dynamic decay coefficient was used instead of a constant value (the best constant value was obtained 0.05hr-1). The concentration of coliform bacteria in Zargan station during the total time of studying is more than 1000 CFU/100ml. Due to coliform bacteria concentrations and compared them with the levels allowed by the Standards, Karun river water is not suitable for human's drinking, confined livestock drink, food industry, oyster farming, irrigation products that are consumed raw and recreational uses (contact with water) like swimming.
somayeh rahimi; mahmood kashefipoor; mahmoud shafai bajestan; ahmad fathi
Abstract
Introduction: Outer bank region is always exposed to destruction and scour due to secondary flow. Different methods are generally used to protect the outer bank. One of the most common and economical ways is spur dike. As an obstacle in the flow, spur dikes protect the outer bank through decreasing the ...
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Introduction: Outer bank region is always exposed to destruction and scour due to secondary flow. Different methods are generally used to protect the outer bank. One of the most common and economical ways is spur dike. As an obstacle in the flow, spur dikes protect the outer bank through decreasing the velocity and forming vortexes between them and as a result sedimentation along that area. However, the spur dike increases the shear stress and local scour around the spur, especially its nose.. This study investigates the scour hole dimensions around three types of spur dike including permeable, impermeable and bandal-like spur dike which is done as a combination of permeable and impermeable spur dike. Few studies were focused on field applications and laboratory experiments to investigate the practical applicability of the bandal-like structure in natural rivers. Rahman et al. (4) Studied the prediction of main channel degradation and local scour around hydraulic structures (impermeable and bandal-like spur dikes) under non-submerged condition. Teraguchi et al. (9) Investigated the influenced of submerged condition on flow characteristics and sediment transport process caused by bandal-like structures with different spacing and alignment under live-bed scour condition through laboratory experiments.
Materials and Methods: Experiments were carried out in the Physical Modeling Laboratory of Faculty of Water Science Engineering of Shahid Chamran University, Ahwaz. The main channel consisted of a 5m long upstream and a 3m long downstream straight reaches. A 90 degree bend was located between the two straight reach. The channel was of rectangular cross section, having a width of 0.7m and depth of 0.6m, with mild bends (ratio of radius to a width equal to 4) and it was filled with almost uniform sediment with a median particle size of D50=1.5 mm. The discharges were measured using an ultrasonic flow meter, which was installed on the pipe inlet of the flume. The water elevation was regulated using the sliding gate installed at the end of the flume. Plexiglas with a thickness of 0.01m was used for impermeable part of spurs and the permeable part prepared by using steel roll piles with 4mm diameter. The most erodible area along the bend was determined and after installing the spurs, the bed surface was leveled by a plate attached to the carriage mounted on the channel. Then the inlet valve was opened slowly and the gate at the end of the flume was first closed. The discharge increased to a predetermined value so that no scour occurs at the straight reaches of the flume. Each experimental case was carried out for 3 hours under clear-water scour condition. At the end of experiments, water was carefully drained out and measurement of bed topography was done using laser bed profiles.
Results and Discussion: The most erodible area along the bend was determined using the procedure described by the U.S. Army Corps of Engineers and in each experimental case specified the critical spur in terms of the maximum erosion around it that happened at the exit of the bend (sections of 80 to 90 degree of bend) and downstream straight reach in all conditions. The centrifugal force will occur has increased the water depth at the exit of the bend. This increase in flow depth is associated with longitudinal negative pressure gradient due to this maximum velocity occurs at the exit of the bend and by this high velocity flow the shear stress increases. The characteristics of the scour hole have been shown to be affected by Froude number and this parameter has a direct relation to maximum relative scour depth and dimensions of the scour hole. The results showed that by increasing the permeability percentage, the amount of maximum relative scour hole depth, length and width decreased. The amount of relative scour depth in permeable and bandal-like spur dike decreased (62% and 55%), and (87% and 76%) for permeability of 33% and 64%, respectively in comparison with impermeable spur dike.
Conclusions: The effect of hydraulic structures, with emphasis in the bandal-like structures, on the scour hole geometric dimensions were investigated in this study. Five types of structures (impermeable, permeable and bandal-like with a permeability of 33% and 64%) were tested experimentally. It was found that:
The increase of permeability, reduced scour rate significantly, such that, the maximum amount of depth, width and length of scour-hole was related to impermeable spur dike (with permeability of 0.0%) and the minimum amount belonged to the permeable spur dike with 64% permeability. The performance of bandal-like structures considering the erosion process around the structures show close results compared with permeable spur dikes.
M. Daryaee; S.M. Kashefipoor
Abstract
Abstract
Due to the importance of using clay soil in many constructive projects such as, road foundation, irrigation canals and related hydraulic structures and etc., improvement of the physical and mechanical soil properties has been the main interest of the geo-technique specialists for years. In ...
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Abstract
Due to the importance of using clay soil in many constructive projects such as, road foundation, irrigation canals and related hydraulic structures and etc., improvement of the physical and mechanical soil properties has been the main interest of the geo-technique specialists for years. In this regard different methods such as mixing clay soil with lime or cement have been used. It has been found that adding some other materials such as polymeric material and sand can more improve the properties of clay-lime mixture. In this research the effect of adding soft sand on the clay-lime properties has been investigated. The soil sample was mixed with 0%, 3%, 5%, 7%, and 9% of lime and 0%, 5%, 10% and 15% of soft sand, and totally a number of 20 samples were provided. The samples after maintaining under three periods including, 7, 14 and 28 days, saturation conditions and temperature of 25°C were tested with the unconfined compressive strength instrument. The main results of this research showed that adding only soft sand to the soil could not improve the soil properties, but using it with lime could significantly improve the soil geotechnical properties. It was found that the best mixture for the highest unconfined compressive strength and elasticity module is the a mixture of original soil with 7% and 10% of lime and soft sand respectively.
Keywords: Clay soil, Lime, Soft sand, Unconfined compressive strength, Eelasticity module
A. Roshanfekr; J. Zahiri; M. Kashefipoor
Abstract
Abstract
Rockfill dams are usually used for affecting the flood and reducing the peak discharge. The materials used in these dams will usually make the flow turbulent, therefore Darcy's law can not be used for this kind of dams and the equations based on the non-Darcy flow must be applied. Non-Darcy ...
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Abstract
Rockfill dams are usually used for affecting the flood and reducing the peak discharge. The materials used in these dams will usually make the flow turbulent, therefore Darcy's law can not be used for this kind of dams and the equations based on the non-Darcy flow must be applied. Non-Darcy flow equations are showed in two general ways including: and .One of the main parameters for flow simulation through this type of media is N, which can be specified empirically using experimental data. N is a parameter for flow turbulence and varies from 1 (laminar flow) to 2 (fully turbulent flow). One of the problems with some of non-Darcy equations (e.g. Ergun) is that they can not compute and N directly. In this research using the Ergun equation and mathematical analysis, a few equations have been derived and presented for computing N and and finally a new equation has been presented for the equivalent hydraulic conductivity (Ke) coefficients in porous media. A standard example was used for the verification of the resulting equations. Some values were assumed for the soil properties and the value of N, were computed using the proposed equations in this research study. N was also specified using a non-linear regression analysis and was compared with the corresponding values obtained from the proposed equations. Comparison of the both sets of results showed that the computed N values are relatively precise especially for the boundaries (N=1 and 2).
Keywords: Non-Darcy flow coefficient, Ergun equation, Turbulence, Equivalent hydraulic conductivity
M. Daryaee; M. Kashefipoor; J. Ahadiyan; R. Ghobadiyan
Abstract
چکیده
احداث ساختمان ها و سازه های مختلف، باعث به هم فشرده شدن ذرات خاک و در نتیجه نشست خاک می گردد. نشست خاک تابع عوامل مختلفی مانند تغییر شکل فشاری، خارج شدن هوا و آب ...
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چکیده
احداث ساختمان ها و سازه های مختلف، باعث به هم فشرده شدن ذرات خاک و در نتیجه نشست خاک می گردد. نشست خاک تابع عوامل مختلفی مانند تغییر شکل فشاری، خارج شدن هوا و آب از خلل و فرج و ... می باشد. یکی از روش های محاسبه نشست، استفاده از شاخص فشردگی است که از طریق آزمایش تحکیم بدست می آید. تعیین این ضریب از طریق آزمایش تحکیم بسیار وقت گیر است. لذا از گذشته سعی بر این بوده که شاخص فشردگی را به پارامترهای فیزیکی خاک از قبیل حد خمیری، حد روانی، نسبت پوکی، چگالی نسبی که همگی به سادگی قابل اندازه گیری هستند، ارتباط دهند. به همین جهت روابط تجربی زیادی در این خصوص ارائه شده است. در این مقاله با استفاده از شبکهی عصبی مصنوعی5 (ANN) ، همبستگی آماری بین خصوصیات فیزیکی خاکهای ریزدانه و شاخص فشردگی مورد بررسی قرار گرفت. همچنین یک واسنجی بین روش های تجربی مختلف موجود برای تعیین شاخص فشردگی با شاخص فشردگی اندازه گیری شده در آزمایشگاه صورت پذیرفت. نتایج نشان داده است که رابطه رندون و هررو از میان روابط تجربی با بالاترین ضریب همبستگی و کمترین درصد خطا، بالاترین دقت را در برآورد شاخص فشردگی دارد. در مقابل شبکه های عصبی مصنوعی شاخص فشردگی را با دقتی بالاتر و درصد خطای کمتر از رابطه رندون و هررو برآورد می کند. همچنین کالیبره کردن ضرایب رابطه رندون و هررو با استفاده از مجموعه اطلاعات موجود، تاثیر چندانی در دقت این رابطه برای تخمین شاخص فشردگی خاکهای منطقه مورد نظر ندارد.
واژههای کلیدی: خاکهای ریزدانه، شاخص فشردگی، شبکه های عصبی مصنوعی، خصوصیات فیزیکی خاک
K. Esmaili; S.M. Kashefipoor; M. Shafai Bejestan
Abstract
Abstract
For investigating the effect of bed form in alluvial channels on the amount of bed load transport, a set of experiments was carried out in a tilting flume under unsteady flow conditions (hydrograph). The produced hydrographs were in triangular form with a maximum discharge of 30 to 45 lit/s/m. ...
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Abstract
For investigating the effect of bed form in alluvial channels on the amount of bed load transport, a set of experiments was carried out in a tilting flume under unsteady flow conditions (hydrograph). The produced hydrographs were in triangular form with a maximum discharge of 30 to 45 lit/s/m. Three size of sediment particles were used with equal to 1.5, 2.1 and 3.0mm, clear water without any feeding was supplied from upstream. To analyze the time varying of bed resistance, a numerical model with initial and boundary conditions was used and its outputs were depth, velocity and discharge. The results showed that the inflow made considerable erosion at the starting time of flowing near the channel inlet, and this is a cause of producing bed form, increasing roughness and bed resistance. However, by the time the erosion trend was declined with increasing discharge. Despite of increasing flow turbulence, Froude number and bed erosion decreased gradually when the discharge approaching to its maximum value increasing flow depth. In this process, because of bed elevation changing along the flume, Froude number at any point is different from the other points and bed particles move toward downstream as a progressive wave. The bed resistance coefficient, n, was increased at the start of inflow time and after a proper time it was again increased, and this matter has very important role in sediment transport for non cohesive beds.
Key words: Movable bed, Bed form, Coefficient roughness, Unsteady flow
K. Esmaili; M. Shafai Bejestan; M. Kashefipoor
Abstract
Abstract
To investigate the effective parameters and simulate the conditions under which sediments are transported in ephemeral rivers and compare it to perennial rivers a series of experiments were performed in a laboratory flume. The hydrodynamic equations were solved for initial and boundary conditions ...
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Abstract
To investigate the effective parameters and simulate the conditions under which sediments are transported in ephemeral rivers and compare it to perennial rivers a series of experiments were performed in a laboratory flume. The hydrodynamic equations were solved for initial and boundary conditions using numerical method. Triangle hydrographs with time duration of 40, 60 and 80 seconds and five different flow rates for each situation were considered. Three slopes of 0.006, 0.014 and 0.018 were selected. A fine and uniform sand with d50 of 1.5, 2.1 and 3 mm from river materials was used as the mobile bed. Clean water (with no sediment) was used. The results of 85 experiments showed that the bed slope was the most important parameter in sediment transportation and it could be used for predicting the sediment transport. The base time of hydrograph was also found to have an effective role in sediment transport, and the results showed that by increasing the base time the transported sediment was decreased. The bed form had a big role on the flow resistance and also affected the sediment transport. The sediment ratio of unsteady to steady flow found in this research was found to be similar with those of Tun Lee.
Key words: Ephemeral rivers, Perennial rivers, Bed load, Sediment
