فهرست مطالب مسیح ذوالقدر

Bucket foundation is a new foundation concept developed in the last decade for offshore wind turbines. Due to easy and faster installation with significantly lower expenses compared to the conventional foundations such as gravity bases and mono piles, suction caissons foundations are reliable and alternative foundation solutions. In this study push-over analysis was utilized to investigate the response of a typical monopod offshore wind turbine foundation under monotonic loading condition. Finite Element Method was used to define and analyze different scenarios.

Rainfall-runoff modeling is considered one of the important methods in the study of hydrology and environmental management, especially in urban areas, in which sudden floods lead to significant financial and human losses. Thereupon, various models have been developed for urban flood simulation, among which selecting the best, is of significant consideration in the literature.

Runoff peak flow and hydroghs measured in three nodes of an urban drainage network were applied for both spatial and temporal evaluation of the SWMM hydrological model in EPA SWMM, ASSA and Bently SewerGEMS V8i softwares. Other rainfall-runoff models also evaluated were SCS TR-55, SCS TR-20, Rational, Dekalb Rational, Santabarbara UH models (in ASSA software) and SCS UH model (in SewerGEMS V8i software). The models were calibrated considering the measurements during three precipitation events, and then validated by the measured data of three other events. The Nash-Sutcliffe coefficient along with the BIAS coefficient, the Coefficient of Determination and the Root Mean Square Error were used as the efficiency indicators.

The measured runoff peak flow and hydrograph were most compatible with those simulated by SWMM models of EPA SWMM, SewerGEMS V8i and ASSA softwares, respectively. Regarding the results of the partial parameter and the Spearman correlation coefficient methods, model outputs were most sensitive to the percentage of impervious areas, equivalent width, roughness coefficient of impervious areas, the depth of depression of impervious and pervious areas, the percentage of impervious areas without surface storage and the curve number, respectively. The model was not sensitive to the roughness of the permeable areas. The results suggest EPA SWMM as the software with more reliable simulation results for runoff management projects in the study area and urban basins alike.

One of the most important policies of water-scarce countries such as Iran is the desalination of seawater for industrial, agricultural and drinking use. Before desalinating seawater, it needs to be transferred, which is a costly process. In this research, the flap-type wave energy converter was considered to provide the necessary energy to transfer seawater to a desalination plant by merely using wave energy. For this purpose, the effects of wave energy converter parameters (paddle width and height), flow properties (water depth and wave frequency), and the slope of the shore on the performance of the wave energy convertor were investigated in a laboratory study. Although the efficiency naturally increased with increasing width of the flap, it should not exceed a certain limit. In short, with 35% and 71% increase in the width of the flap, the output pressure increased 1.58 and 2.82 times, respectively. An increase of 13% and 27 % in water depth first led to a maximum increase of 3.44 times in water pressure and then led to a decrease of a maximum of 1.68 times. Experiments with the height of the flap also showed that when the rotating flap was non-submerged, the water pressure of the device was at least 2.05 times higher than that in its submerged state. For the slope of the shore, with 63% increase in slope (from 1: 5 slope to 1: 3 slope), the pressure increased by 47.25%, and when the slope was increased five times (from 1: 5 slope to vertical slope), the pressure increased by 2.14 times.  For the period of the wave, with a 15% increase in the period, the pressure decreased by 17.02%, and for a 25% increase in the period, the pressure decreased by 81.58%. In this study, a total of 165 experiments were performed and the flap-type wave energy converter was evaluated as a suitable and low-cost method for transferring seawater to shore.

Energy dissipation in stepped spillways is one of the primary goals of such structures. In this study, the accuracy of the artificial neural network (ANNs) method, the adaptive fuzzy neural inference model method based on the trained firewall optimization algorithm (ANFIS-FA) and the gene expression programming method (GEP) in estimating the energy loss of skimming flow regime on stepped spillways has been studied. Also, by performing sensitivity analysis, the importance of input parameters in predicting energy loss for each of the three mentioned methods has been investigated. For this purpose, 154 series of laboratory data have been used. The input parameters for each method include the hydraulic jump Froude number, the Drop number, the number of steps, the 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 than classical methods for estimating energy loss based on conventional regression methods. The accuracy of the ANFIS-FA (with) method is slightly higher than the GEP (with) method. The accuracy of the neural network is slightly lower than the above two methods.However, the highest accuracy obtained is related to the multilayer perceptron neural network with 3 hidden layers with the number of 12, 8 and 7 nodes in each layer, respectively. In all three methods, the most effective parameter is the waterfall number and the least effective parameter is the pseudo bottom slope.

Installation of stone particles is a very common method to protect abutment against scour. An alternative is concrete elements. In this research, installation of pebbles, Six-Legged Concrete (SLC) elements and combination of them is studied in laboratory. SLC elements were installed in open and dense arrangements with three different depths; on the bed, under the bed and the median case around wing-wall and vertical-wall abutment. Generally, results showed the significant effect of scour mitigation when both methods were applied so that, the maximum scour depth at the abutment toed was reduced up to 70% in vertical wall abutment and totally eliminated at the wing wall abutment. Edge failure was observed when the best scour reduction was achieved in SLC elements installation case. However, best countermeasure was achieved when both methods were applied while edge failure was also controlled. Transformation of the maximum scour depth from the abutment toe to the channel midway at the downstream of the abutment is also discussed.

Introduction:

 Time of concentration (TC) is the time in which a water parcel travels from watershed divide to its outlet. Time of concentration is also the most important factor in selecting design discharge for an area, since the most severe floods are those caused by rainfalls with durations equal to the concentration time of a watershed. Time of concentration is necessary in the studies of water resources management, flow volume and discharge estimation, design of spillways and hydraulic structures, development of flood predicting models, flood alert systems, river management and drainage projects and many other water related studies. There are various empirical methods for calculation of concentration time. The focus of this study is to simulate the water parcel to calculate the time of concentration with a two-dimensional hydraulic model (HEC-RAS 5.0.7). To the knowledge of the authors this method has never been applied for estimation of time of concentration.

Currently there are two main methods to evaluate the time of concentration; applying empirical formulas or applying graphical methods with requires flood hydrograph and corresponding rainfall hyetographs. Due to the differences in the accuracy levels of empirical methods in different areas, along with the unavailability of graphical methods in most of the watersheds, this study aims to estimate TC, using the basic definition of time of concentration which is the travel time of a water parcel from basin divide to the outlet. Two-dimensional HEC-RAS model was used to navigate the runoff flow in the main channel of a watershed from the farthest hydrological point to the outlet. Besides, 48 different empirical equations were gathered from the literature and used to estimate the time of concentration. In order to validate the numerical method and the empirical formulas, the actual concentration time of the flow is measured by salt solution tracking. Then, the comparison of the measured data with the results of the numerical and experimental methods is made, using the percent of error index. Ali Abad watershed of Fars province has been considered as a case study due to the appropriate data availability and the possibility of various measurements as described in the following sections.

Results showed that only 5 methods indicate relative errors less than 20% of which 4 belong to the empirical formulas (8% of the total empirical methods) and one to the numerical simulation. The NRCS is also a well-known equation in which runoff flow in a watershed is divided into three parts: sheet flow, concentrated shallow flow and open channel flow. Flow velocity is estimated by the Manning's relation in the reach according to this method. This method’s accuracy is about 82%. In order to run the two-dimensional model, DEM of the area with 10 meters’ accuracy was used to define the bathymetry. Manning roughness coefficient was also calibrated for model tuning. Over ally the best results were obtained from the hydraulic simulation when applying bank-full discharge equal to 3.53 cms so that the error of this method was limited to 3%. Hence, it is wise to accept the computational costs of a two-dimensional hydraulic simulation to predict the time of concentration instead of empirical formulas, Since the results might be used to construct costly hydraulic structures.

Different methods of concentration time estimations were evaluated and compared with the actual concentration time obtained by salt solution tracing in Aliabad watershed of Fars province. Two-Dimensional simulation of the water parcel from the basin divide to the outlet was also performed by HEC-RAS 5.0.7. The results indicated that among empirical relations, the concentration time value obtained from the Simas and Hawkins equation is much closer to the actual value and is considered as the best empirical equation for Aliabad watershed. This equation involves river length and slope, watershed area and surface storage. Following Simas and Hawkins, equations developed by SCS, SCSlag, Yen and Chow, and NRCS gave closest estimations to the actual concentration time, respectively. However, the results of hydraulic simulation show the most accuracy depending on water parcel definition. That is because, the two-dimensional model takes the topography, local slope, roughness and geometry of the water body into account and is a reliable technique to estimate the time of concentration in any desired location. Nevertheless, for empirical relations it is necessary to realize the limitations of each method and compare it with the study area. Hence, it is recommended to apply hydraulic simulation instead of empirical formulas to estimate the time of concentration. Also, with the measurement data, the results of this study can be used as a criterion for measuring concentration time in similar hydrological studies.

Sand and gravel are essential materials for developing purposes in infrastructures and many various purposes. Iran, is a developing country and numerous infrastructure projects all around the country are under construction. This issue, demonstrates the growing demand for sand and gravel harvesting. Irregular and non-technical harvesting of sand and gravel from rivers, plays an important role in unwanted morphological and environmental side-effects. Physical modeling and numerical simulation are two main techniques to investigate this phenomenon. Considering the high cost of constructing physical models, application of numerical tools for simulation of hydrodynamics and sedimentation has made a significant help for understanding the related phenomenon including the effects of sand and gravel removal in different rivers. In this study, the accuracy of the MIKE21 as a two-dimensional numerical tool, in simulation of sand harvesting hole displacement was investigated by comparison with laboratory data. For this purpose, nine experiments with different dimensions of excavation holes were designed in a 10 m long and 0.7 m wide laboratory flume with uniform sand bed materials. (D50=0.71mm). Two types of triangular and trapezoidal excavation holes were tested. Four important point plus depth and area of the excavated hole were considered as base points of comparison between simulated and experimental results. The flow depth was constant during all experiments (12 cm) and clear water condition was considered (v/vc=0.95). Acceptable agreement between numerical and experimental results was observed. However, the accuracy of the model was more in larger holes whereas the maximum error in predicting the migrated hole geometry in trapezoidal holes was about a half of triangular ones. After verifying the numerical model in laboratory, a specific reach in Helleh river was considered as a case study. Initially one-dimensional model of the river was simulated with HEC-RAS. 25 years return period flow hydrograph was introduced as the upstream boundary condition. Normal flow depth at Helleh Lagoon and time series of the water surface elevation changes of the Persian Gulf were introduced as two downstream boundary conditions. The boundary conditions of the selected reach for   two-dimensional modeling were extracted from one-dimensional simulation. After setting up the two-dimensional model, the effect of sand and gravel mining on a bridge in the reach was investigated in two different scenarios. The distance of the sand mining hole to the bridge was selected as 1000 m and 100 m respectively in two scenarios. It should be noted the simulation was conducted only for a 25 years return period within 16 days. More severe floods can leave more significant effects on the river and in-line structures. The results indicated that for a flood event with a return period of 25 years which was considered for simulation, sand and gravel mining had changed the hydraulic parameters and bed profile significantly, so that the flow depth at the vicinity of the excavation hole was raised up to 77% in second scenario. The flow velocity was reduced up to 75% in the first scenario and the bed profile was decreased up to 1.27m at the foundation of the bridge in the second scenario. Initial signs of river meandering were emerged in the second scenario where the flow was deviated to the mining hole.

Studying the flow pattern at lateral intakes where separation occurs is a critical issue. The flow rate and sediment trap is 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 turnout efficiency by decreasing the flow effective area at lateral intakes. It also creates a region with horizontal vortices where is prone to sedimentation. Hence, application of methods to reduce the separation zone dimensions is of important significance. 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 effect of roughness coefficient and drop implementation at the entrance of a 90-degree lateral intake on the dimensions of the separation zone. As far as the knowledge of the authors show, these two variables have not ever been studied as methods to decrease the separation zone dimensions and enhancing the turnout efficiency.

In order to investigate the effect of roughness coefficient and drop implementation on the separation zone dimensions, four different discharges (16, 18, 21, 23 l/s) in subcritical conditions, seven manning roughness coefficients (0.009, 0.011, 0.017, 0.023, 0.030, 0.032) and 3 invert elevation differences between the main channel and lateral intake (0, 5 and 10 cm) at the entrance of the intake were considered. Totally 84 tests were performed in a concrete flume with 15 m length 0.5 m width and 0.4 m depth. The intake structure was made at a 90-degree angle to the main channel with 0.35 m width. The Manning roughness coefficient values were selected based on available and also feasible value for real condition, so that 0.009 is equivalent to galvanized sheet roughness and selected for the baseline tests. 0.011 is for cement with neat surface, 0.017 and 0.023 are for unfinished and gunite concrete respectively. 0.030 and 0.032 values are for concrete on irregular excavated rock. (Chow, 1959). The roughness coefficients were created by gluing sediment particles on a thin galvanized sheet which was installed at the upstream side of the lateral intake. The values of roughness coefficients were calculated based on Srickler’s formula. For this purpose, some uniformly graded sediment samples were prepared and the manning roughness coefficient of each sample was determined with respect to D50 value pasted into the Strickler’s relation. All the experiments were recorded and photographs were taken severally during the experiment and after steady flow conditions were established. The photos were then imported to AutoCAD to measure the separation zone dimensions. The velocity values were also recorded by a one-dimensional velocity meter at 15 cm distance from the intake entrance and in transverse direction (perpendicular to the flow direction).

Negative velocity values were recorded in the separation zone indicating dominant secondary currents at the intake entrance. The velocities were intensified by moving toward the intake midway showing that the effective area is scaled down. The velocity values were almost equal to zero near the side walls as expected. Results were presented as dimensionless separation zone area (ratio of the separation zone area to intake area). Analysis shows that by increasing roughness coefficient alone, separating zone dimensions reduce up to 38%. This technique requires minimal changes in intake geometry and is definitely an inexpensive method to be applied for intakes under operation. Besides roughness coefficient studied were quite accessible. Implementation of drop can decline this area respecting the roughness coefficient value differently. Naturally there is an invert elevation difference between the feeding canal and the areas to be irrigated. This idea was developed base on this issue. A minor part of this difference can be compensated at the intake entrance. This method increases the discharge ratio (ratio of intake to main channel discharge). The results are compatible with literature. Some other researchers reported that intensifying the discharge ratio can scale down the separation zone dimensions (Rumamurty et al., 2007. Keshavarzi and Karami Moghaddam, 2007). However, these scientists employed other methods to enhance the discharge ratio. Employing both techniques simultaneously can decrement the separation zone dimensions up to 41%. A comparison between the new methods introduced in this paper and traditional methods such as installation of submerged vanes, and changing the inlet geometry (angle, radius) was performed. The comparison shows that the new techniques can be highly influential and still practical.

This study introduces practical and still easy and costly beneficial methods for enhancing intake efficiency by declining the separation zone dimensions. Increasing roughness coefficient and implementation of inlet drop were considered as remedied for reduction separations zone dimensions. Results showed that enhancing roughness coefficient can decline the separation zone dimensions up to 38% while drop implementation effect can scale down this area differently based on roughness coefficient used. Combining both methods can descend the separation zone dimensions up to 41%. It is proposed to investigate the effect of roughness and drop implementation on sedimentation pattern at lateral intakes for further researches.

In the recent years, the failure of many bridges has reported due to local scour around abutment. Many studies have focused on reducing the scour with the help of structures reducing the destructive effects of flow. In this study, the scouring effect on two vertical wall abutments with different widths was investigated using clean water. Where the upstream face of the latter is protected with roughening elements as devices to intercept the down flow responsible for the formation of the principal vortex. Different sizes of the elements with thicknesses and protrusions equal to 0.025L, 0.05L, 0.1L, 0.2L and 0.3L (L is the length of the abutment) placed at different elevations on abutments were investigated. The optimum elevation of roughening elements obtained at 0.6L below the bed level. As the thickness and protrusion dimensions of the elements increases to 0.2L, scour depth around the abutment decreases, and after that increases if the element size become larger. In conclusion, the roughening elements with thickness and protrusion equal to 0.2L and placement of 0.6L below the sediment bed reduced the scour depth 30.4 and 32.8% at the small and large abutments, respectively.

The reviews of past researches have shown that abutment scour plays an important role in bridge failures. Hence, protection of bridges against scour is a significant issue. For existing bridges, armoring methods, like riprap, has a wide application. In areas where providing stones is expensive concrete blocks or similar techniques have been applied. In this study for the first time, the application of six-legged concrete elements has been experimentally investigated. The six-legged elements have been placed in three different densities (open, medium and dense) and three different placement depths (under the bed, above the bed and medium case). Each alternative have been tested under different flow conditions. Generally the results proved that the six-legged elements can considerably reduce the scour depth under different flow conditions so as it reduced the maximum scour depth of abutment nose up to 100%. The maximum reduction of scour depth has been obtained when the high dense six-legged elements are placed above the bed. In this case, the elements protect the abutment by creating coverage and also alter the sour from the abutment tip to the channel midway.

Bridge failures are fortunately rare, but every year a number of bridge collapse that has occurred somewhere in the world. In many cases these collapses could have been avoided by an adequate bridge management regime that included good inspection, assessment and maintenance procedures. One specific type of failure that from time to time causes sudden catastrophic collapse of bridges is the undermining of foundations due to bed scour. Bed scour is the transport of bed material by the flow of water and is present to some degree where the river bed is formed of granular material. Scour increases as flow rates increase and therefore the actual collapse of structures due to scour often occurs during periods of extreme flow due to flooding. Of course, this is exactly the time that direct observation of the foundations of a structure is not possible and therefore a collapse may be put down to an ‘act of God’. A good inspection regime that includes bed measurement and engineering analysis can find indications of developing scour before the situation becomes critical. If this is followed up with well-designed remedial works, undermining of the structure, even in extreme conditions, may be prevented. The formation of scour holes around bridge piers or abutment is one of the main causes of bridge foundation collapse. Local scour at bridge piers and abutment may be defined as a local lowering of the bed elevation. This lowering is mainly caused by the horseshoe vortex combined with the downflow in front of the pier and abutment, the vortex shedding at the back of the pier, abutment and the flow contraction. Bridge failure due to the effects of local scour associated with the structure of the local flow field around piers and abutment involves a considerable interest in scour prediction and scour protection measures. Two basic procedures may reduce the scour depth. The first consists in enhancing the ability of the bed material to withstand erosion. This is generally done by placing an armoring device on the bed, such as riprap. The riprap provides a physical obstacle that resists the erosive power of the flow. The second procedure consists in reducing the downflow in front of the pier and the horseshoe vortex scouring the bed material. The local scour around bridge pier and abutment in recent years has been widely studied by different authors. They proposed different methods to control the scouring depth. The most dominant concern about bridges stability is the occurrence of local scour around foundations. The local scour around bridge piers and abutments has been widely studied by different authors in recent years. They proposed different methods to control the scour depth. In order to reduce scouring around bridge piers and abutments one of the methods is the soil compaction. Compaction rise the relative density and soil resistance which mitigates scour and produce a time delay in scour hole development process. This paper focuses on the effect of clay content percentage and compaction ratio on scour reduction around bridge piers. Hence, 5%, 10%, and 15% clay was added to soil and then compacted. According to the experimental results, when 15% clay was added to non-cohesive sediment materials in saturated bed conditions with a relative density of 70%, the scour process was completely controlled after 24 hours around the bridge pier.

The reviews of past researches have shown that abutment scour plays an important role in bridge failures. Hence, protection of bridges against scour is a significant issue. For existing bridges, armoring methods, like riprap, has a wide application. In areas where providing stones is expensive concrete blocks or similar techniques have been applied. In this study for the first time the application of six-legged concrete elements has been experimentally investigated. The six-legged elements have been placed in three different densities (open, medium and dense) and three different placement depths (under the bed, above the bed and medium case). Each alternative has been tested under different flow conditions. Generally, the results proved that the six-legged elements could considerably reduce the scour depth under different flow conditions so as the maximum scour depth of abutment nose was reduced up to 86%. The maximum reduction of scour depth was obtained when the high dense six-legged elements had been placed above the bed.

Application of 2-D hydrodynamic models for simulation of flow around dike fuse plug spillways is inevitable due to complexity of flow in the vicinity and beyond the breach. Because of popularity of MIKE21 in Iranian institutions، this research tries to assess the performance of MIKE21for this application. First، the performance of MIKE21 in dike breach simulation was assessed using experimental data. After verification of the model results in an experimental case، a case study which was Helleh River near Borazjan، was considered to show the performance of method in a real situations. To specify the initial and boundary conditions، the river reach was initially modeled by 1-D model، HEC-RAS. After comparison of 1-D and 2-D results in prediction of maximum water surface elevation، assuming no dike breach، flow due to fuse plug breaches in several places werestudied in different scenarios. Finally، some issues related to propagation of flow on initially dry bed and wetting and drying were discussed. The computational cost of the 2-D model was also much more than 1-D model.