mohammadhosein omid

Determining the resistance coefficients and reducing the uncertainty in selecting this parameter is one of the most essential factors in achieving the flow characteristics in rivers and open channels. Therefore, the appropriate selection of roughness coefficient in different conditions, such as vegetation, has been one of the important research topics. This research first determined the Manning’s roughness coefficient in a laboratory flume with different vegetation arrangements. Then, the ability of five intelligent models, including GMDH, ANN-RBF, RT, ANFIS, and ANFIS-PSO, to predict the Manning’s roughness coefficient was evaluated. The models were coded in the MATLAB software. Due to the creation of a gradually varied flow in the laboratory flume, the water level profile obtained through Euler's method was compared with the experimental values. The results showed an acceptable agreement between the experimental water level profiles and the estimates made by Euler's method. The evaluation of the results based on the statistics showed that the ANFIS-PSO model performs better than other models in predicting the Manning’s coefficient. Hence, the results of this model are RMSE=0.0096, R2=0.9984 and KGE=0.9922 in the training phase and RMSE=0.0099, R2= 0.9982 and KGE=0.9873 in the test phase. The ANN-RBF, GMDH, ANFIS, and RT models are in the next ranks. By evaluating the results of different combinations in modeling, it was found that three parameters of vegetation density (D), vegetation arrangement (N) and Reynolds number (Re) had, respectively, significant effect in estimating the correct results.

Modeling is one of the most effective methods in river water quality management, planning to reduce the entry of pollutants and control environmental damage. In this article, the water quality of Babolrood river using the Qual2kw model and meta-heuristic model of support vector machine and SVM-GA genetic algorithm with the approach of simulating six water quality parameters including temperature, alkalinity, electrical conductivity, total nitrogen, dissolved oxygen and biochemical oxygen demand in four time periods from 2018 was investigated. Genetic algorithm is used for simulation and optimization, and the hybrid of this model with support vector machine has improved the simulation performance. In order to compare the observed and simulated data, the explanation was used coefficient R2 of the average absolute error MAE and the root mean square of the normalized error NRMSE. The results showed that the best SVM-GA simulation for total nitrogen parameter in February is with MAE 0.15 and NRMSE 1.97. Also, the results of Qual2kw numerical model showed that the best simulation for May is with MAE 0.14 and NRMSE 1.2. The water quality of Babolrood River was evaluated using the NSFWQI index. Based on this, the best water quality is in the month of Bahman with an index of 56 in the medium to good range and the worst quality is in the month of May with an index of 49 in the bad range.

From environmental aspects, the exchange of surface and subsurface flows in riverbeds due to river morphology and in stream structures is very important. The flow path structures especially control structures have a more effective role than the river morphology in the formation of these exchanges. In this study, the effect of penetration depth of such structures in the porous bed on the characteristics of exchange flows was investigated both experimentally and numerically. The experiments were performed in a flume with a length of 10 m, width of 20 cm, depth of 30 cm and a slope of 0.01, at three penetration depths of 9, 11 and 13 cm respectively. Potassium permanganate tracer was used for tracking the flow. In addition, to obtain the characteristics of the exchange flow; the mainstream and the exchange pattern were simulated by particle tracking method using Flow 3D software. The results showed that in the Reynolds range of 1020 to 3450, increasing the penetration depth of the structure from 9 to 13 cm, would increase the residence time but decreases the exchange rate. However, increasing the flow rate would decrease the exchange rate and increase the retention time. Accordingly, the use of a step with a higher penetration depth is recommended to create a longer residence time. However, a step with a smaller penetration depth may be used to produce a higher exchange rate.

One of the issues that researchers have always considered in the design of storage dams is reducing the kinetic energy of flow passing through the spillways to control the velocity, reduce the destructive energy, and scour depth downstream of spillways. Stepped chutes and flip buckets are the most common energy dissipator structures in emergency spillways at dams. Regarding the effect of scour depth at downstream of these structures on their stability and safety, in the present study, the effect of hydraulic and geometric parameters on variations of scour characteristics downstream of smooth and stepped chutes was investigated experimentally. Experiments were conducted at a hydraulic lab at the University of Guilan in 2020-2021 with a ratio of critical flow depth and step height (yc/h) of 0.53-0.97, bucket exit angles of 15° and 30°, the ratio of tailwater and critical flow depth (ht/yc) ranging from 1.5–2, the ratio of height falling and step height (HF/h) varied in the range of 2-4, and a spillway slope of 1:2 (V: H). The comparison of results demonstrated that implementing steps over a smooth chute profile reduced maximum downstream scour depth of the flip bucket by 15° and 30° exit angles in comparison with a smooth chute for the minimum relative critical flow depth by 22 and 41 percent, respectively, and for the maximum relative critical flow depth, by 14 and 20 percent, respectively. Also, with an increase in the exit angle from 15° to 30°, the maximum scour depth decreases for the minimum and maximum tailwater depths by an average of 18 and 11 percent, respectively, for a smooth chute and by an average of 19 and 17 percent, respectively, for a stepped chute. Furthermore, a regression relationship was derived for predicting the scour depth at downstream of stepped chutes with the flip bucket.

In rivers with a compound section, typically the relatively high roughness of floodplains, as compared with the main channel, grounds the speed difference in these two ( main channel and floodplains). The velocity dissimilarity also creates shear layers at the interface point of the main channel and the floodplain. The development of shear layers will also cause turbulence in the mutual plane of the main channel and the floodplain. In such conditions, the average flow speed cannot be applied to compute parameters such as shear stress, bed-load discharge, and so forth. Laboratory experiments was carried out to investigate the effects of floodplain divergence on flow hydraulic and the rate of sediment transport through roughness and different divergent angles. This research 36 tests were done at a concrete flume with compound channel cross section (9 and 27 tests with prismatic and Non-prismatic cross section respectively). By using a micro-propeller and ADV (with 200 Hz frequency) in different sections the velocity were measured. For depth ratio of 0.15 0.25 was used the micro-propeller and depth ratio 0.35 was used the ADV. The results reveal that the increase in all three factors of roughness, divergence angle, and relative depth cause dramatic changes in hydraulic of flow and sediment transport.

In this research, in order to develop new relationships with reasonable accuracy for estimation of the ýsubmerged hydraulic jump characteristics, a study has been conducted experimentally. Experiments have ýbeen done in a rectangular channel with a length of 9 m, a width of 0.5 m and a depth of 0.45 m. Froude ýnumbers in these tests range from 3.5 to 11.5 and between submergence ratios of 0.1 to 4. According to the results, the water surfaces profiles have been obtained in different Froude numbers and submergence ýratios. Also, some relationships with high accuracy to estimate such characteristics as jump length, ýsubmerged depth on the gate, and the relative energy loss have been developed. The results also showed ýthat, in a given Froude number, length and relative energy loss for submerged hydraulic jump are, respectively, more and less than those for free hydraulic jumps. In addition, for submerged hydraulic jump, ýat a given Froude number, by increasing the submergence ratio, the jump length and submergence depth on the gate increases and relative energy loss decreases. Finally, using sensitivity analysis technique, the ýeffectiveness of dominant parameters on the developed expressions on the changes in submergence depth ýon the gate parameters and relative energy loss has been determined.

This paper presents the results of an experimental program developed to investigate the effect of an additive agent branded CBRPLUS on the mechanical behavior of a forest soil with high plasticity. Various experiments consisting of Atterberg limits, standard compaction, California bearing ratio (CBR), swelling potential and swelling pressure were conducted on natural soil and soil stabilized with various percentages of CBRPLUS. The results indicated that the addition of this material (at the rate of 0.05%), significantly changes the physical and mechanical properties of rehabilitated soil, including, reduction of the liquid limit (at least 6%), plasticity index (at least 9%), swelling potential (at least 27%), and swelling pressure (at least 45%), and also increasing the bearing capacity of soil (at least 53%); hence, the improvement of soil properties is a function of mass percentage of CBRPLUS. Furthermore multiple regression models were developed for CBR, swelling potential and swelling pressure as a function of additive agent percentage, plasticity index and maximum dry unit weight with accuracy and a high degree of agreement between experimental and predicted values. In addition a sensitivity analysis was also performed to investigate the effect of various parameters on CBR, swelling potential and swelling pressure values.

Longitudinal dispersion coefficient is normally affected by many hydraulic parameters. So far three approaches namely, integral method, dye tracing filed measurements and empirical formulae have been widely used to estimate the above mentioned coefficient, in rivers and streams. In this paper a new equation of the longitudinal dispersion coefficient is determined and evaluated using an environmentally safe tracer and the basic empirical equations. To achieve this aim, a length of 500 meters of a mankind concrete canal was chosen, to carry out the tracer tests. A set of experiments was conducted in three different mixing lengths, including 45, 75 and 100 meters in Feb. 2015. The results show that differences of average, variance and maximum concentration between measured and estimated data using the past equation are equal to 79, 6, and 99 mg/lit and using the equation in present study equal to 66, -1 and 44 mg/lit, respectively.

Due to environmental considerations, using permeable control structures in rivers have been widely welcomed by engineers working on different aspects of rivers. Impermeable structures such as rockfill dams could provide more suitable hydraulic conditions for flow discharge within rivers by allowing sediments pass through their body so that the environmental impacts at structures downstream may be reduced to its lowest rate. Although there are a large number of researches carried out on the hydraulics behavior of the flow passing through fine and coarse materials, there is, however, a few studies on passing bed load through dam body of rockfill structures. In this experimental research, to provide suitable condition for bed load to pass through dam body, a coarser layer of materials has been used at the bottom of the dam. Using dimensional analysis and data provided from laboratory tests, a relationship to estimate the amount of bed load passing from coarse materials has been introduced, and in this regard, the available equations to estimate bed loads, are modified as well. The mean relative error of the new equation was estimated as 64.7% while it is estimated as 101% for Meyer- Peter and Muler modified relationship. Furthermore, it is found that at the range of the experiments carried out in this research, using coarser materials at the bottom of rockfill dams has no significant effects on the amount of bed load passing through dam body.

The accurate estimation of reaeration rate coefficient، because of its effects on dissolved oxygen in rivers، is one of the most important initial steps of water quality management. The main goal of this paper is to evaluate the effects of reaeration coefficient on the river water dissolved oxygen، case study Dinachal River، Iran. To achive these aim، water quality samples were collected along a reach of 2 kilometers of the river in September 2013. Electrical Conductivity، pH، Dissolve Oxygen، Biochemical Oxygen Demand، Nitrate and Phosphorus are the main quality parameters which were measured in laboratory، using the above mentioned collected water samples. Streeter-Pheps model has been used to simulate dissolved oxygen in the river analyticaly and to improve the output of the model; advection، disspesion and decay rate terms were included to the basic form of the Streeter-Phepls equation. In addition، dissolved oxygen concentration in the river has been simulated involving FTCS، QUICKEST، Upstream and Lax-Wendroff numerical methods. The reaeration coefficient has been estimated using four empirical equations including; Oconnor-Dobbins، Langbein-Durum، Boulton and Ling et al.. The results show that Up-stream numerical method containing Boulton reaeration Coefficient equation has the most accurate results، whith the amounts of Pearson correlation coefficient and Mean Absulate Errors equal to 0. 995 and 0. 033، respectively.

Piping sometimes is occurred due to seepage of water in hydraulic structures. The continuty of this phenomenon decreases the safety or caused the failure of a structure. In this work، experimental tests were carried out on statically compacted natural and randomly reinforced silt sandy soil samples. The randomly reinforced samples were prepared with different lengths and percentages of an artificial fiber. The tests were done in special designed and made apparatus. During the tests، seepage velocity، hydraulic gradient، permeability and seepage force were measured and calculated in different samples and compared with natural soil. The results showed that in the case of randomly reinforced soil، the resistance of soil against piping was increased. in addition، the increasing of the length and percentage of fiber also have important role in improvement of soil.

The effect of a submerged normal flat plate on the trap efficiency and sedimentation length of a settling basin was experimentally investigated in this study and compared with the results of a numerical model. The implemented numerical model is an Eulerian-Lagrangian model that solves The Reynolds-Averaged Navier-Stokes equations with k¾e turbulence model for the continuous phase and sediment particles are tracked with a lagrangian method. The results indicate that, when the linear transition transmits the flow with high momentum from the upstream canal into the basin with no extra turbulence and a parallel 2D flow is established in the basin, the baffle has no positive effect on the trap efficiency and the sedimentation length.However, in 3D conditions in which the incoming jet travels a considerable distance and causes large variations of transverse velocity in the basin, installing the baffle in a relative submergence of 15% can increase the trap efficiency of the settling basin by up to 8.5%. This may be attributed to the role of the baffle in decaying the kinetic energy of the impinging jet and spreading the sediment particles in the width of the settling basin.

The occurrence of transcriticalor mixed flow, i.e., supercritical and sub critical flow regimes, is considered as a special case of unsteady flow in a channel reach, which can clearly be exemplified by a moving hydraulic jump. Some complexity is inherent in the numerical analysis of transcritical flow and published experimental data regarding this kind of flow are rarely available. In this research an experimental setup was prepared to compile the hydraulic characteristics of transcritical flow in a rectangular flume. The flume was equipped with a sluice gate at the upstream boundary. Each inflow hydro graph generated unsteady supercritical flow regime at the downstream side of the sluice gate and formed a moving hydraulic jump along the channel. During each run, the water surface profile was continuously recorded using a pressure transducer. Based on the recorded data, some flow parameters such as flow depth, pressure head and energy head were determined. The result reveals specific relations between the discharge and moving hydraulic jump parameters. Also, by applying proper assumptions and employing steady state momentum and energy equations simple yet reasonable (and time independent) relations were obtained, that determines the pressure head in subcritical region of unsteady mixed flow. Consequently, having the discharge variation as a boundary condition, one may reliably determine the unsteady transcritical flow parameter based on time independent relations.