MODARES TECHNICAL AND ENGINEERING
Year:2006 | Volume:- | Issue:25|Papers Count:11

Numerical solution of turbulent flow at a 90-degree diversion in a straight channel with rectangular cross-section, using Fluent software, and investigation of 3D flow pattern and distribution of wall shear stress in main and branch channels are the principal goals of this paper. Computations have been done for different discharge ratios and turbulence has been modeled using two closure models:standard k- e model and k-w model of Wilcox. Numerical modeling results have been compared with available experimental results and velocity profiles along the main and branch channels have been investigated. The strength of secondary flow along the branch channel has been studied and the effect of discharge ratio on this phenomenon and the relationship between this phenomenon and the circulation zone along the branch channel has been investigated. The wall shear stress contours have been plotted and variation of this parameter at the bed planes of main and branch channel have been studied. It is found that both turbulence models used accurately predict velocity profiles in the main channel but in the branch channel, the k-w model performs better than the k-e. Numerical modeling results showed that there is another separation zone at upstream corner of lateral intake inlet. This zone has an opposite rotating direction with respect to the main separation zone.

Expansive behavior is usually observed in soils, which contain fractions of clay minerals in their composition. Water absorption of clay particles and change of natural water content of soil up to plastic limit and down to shrinkage limit will cause significant volume change in expansive soil and will result in severe damages to the structures, buildings and foundations. Swelling potential is directly related to clay minerals activity and soil plasticity. Besides all the parameters expressing composition of soil, environmental conditions provide conditions to release the swelling potential.In the present study, in order to observe effects of soil mineralogy, plasticity, and compaction indices such as water content and dry unit weight, swelling behavior of five clay soils has been investigated. Results of experiments indicate that parameters like clay minerals, absorbed cations to clay sheets, plasticity index, clay size fraction, initial water content and dry density have significant influence on the swelling behavior of compacted clays.

In this paper, different variables affecting the rate of highway accidents were studied and a mathematical model for assessment of highway safety is proposed. Field data as well as necessary information was collected form about 580km of main roads including different classes and various terrain conditions throughout the country. The modeling process was followed using linear functions, based on the collected data from the variables. Comparing the correlation coefficients of these models, the Poisons Regression Model was perceived as the most appropriate one, which was then calibrated and verified using the information for a six-year period. The dependent variable was defined as an accident index, AI, representing the number of accidents and their severity. Formation of commercial and residential land uses by the roadside considerably increases the rate of accidents. Mountainous roads are thirteen times more dangerous than level roads moreover, increasing the rate of heavy vehicles by 10%, will increase AI by 60%. Also changing the function of a two-lane highway to a onelane results in a decrease of AI by 60%. Addition of one lane to the roadway, and increasing its shoulder width by one meter will improve safety index by 50 and 60 percent, respectively.

The individual penetration of aggregates is an important problem in the construction of breakwater on soft seabed. Any overall resisting mechanism of the foundation could not be formed when aggregates are individually penetrating seabed. In this situation a large volume of breakwater material penetrates into bed. In design, "aggregate local penetration" control should be considered in addition to usual controls such as bearing capacity and settlement. In this paper, with the use of proposed laboratory method, penetration of aggregate into soft soil is investigated. In addition to laboratory studies, some breakwaters that constructed on soft seabed in the south coasts of Iran were studied. Finally, it has been concluded that fine mattress decreases penetration of aggregates. A relationship is proposed for determining mattress thickness.

Some of existing concrete structures have some deficiencies due to low material quality or design. In recent years, the retrofit of nonresistant or damaged reinforced concrete members with external bonding of fiber-reinforced-polymer (FRP) laminates has received considerable attention. The objective of this study is to examine effects of glass-fiber-reinforced-polymer (GFRP) composite rehabilitation system on the reinforced concrete beams. Experiments were conducted on beams with and without GFRP composite sheets on their tensile surfaces. A total of 16 beams were tested. 8 beams were tested under static loading, while the remaining 8 beams were subjected to cyclic loading.Specimens were 200*300*2000 mm reinforced concrete beams with enough transverse reinforcement to avoid shear failure. The main parameter in the test study was the number of layers of GFRP laminates. The experimental results show that, bonding GFRP laminates improves both flexural capacity and stiffness of beams. Moreover it reduces the quantity and width of cracks, and limits the destruction in rapture zone. Evaluation of load-deflection curves shows the favorite behavior of strengthened beams under cyclic loading. Results of different tests have very good agreement with the application of analytical equations.

Y-shaped concentric bracing exhibits a unique behavior of producing tension or compression in all of its three members under horizontal loading in plane of bracing. So far, the use of this bracing has been justified with regard to its stable behavior when its members are tensile. Considering the limitation of horizontal component of tension in bracing to 70% of total shear in Iranian standard 2800, it is necessary that y- bracing be able to resist at least 30% of total shear by compressive internal forces. In this research, performance of y-bracing with compressive members is investigated. Out of plane buckling is the most probable mode of failure of y-bracing. Observing the importance of flexural fixity of member supports in determining the out of plane buckling load, the critical load is computed assuming connections formed by steel plates welded to both sides of bracing members. Calculations show that y-bracing has considerable capacity to resist lateral force producing compression in its members. Variation of critical elastic load due to variation in location of convergence point of members is studied. The highest elastic critical load occurs with convergence point on the full diagonal member. Moving the convergence point towards the frame corner reduces the elastic load.Elastic buckling load has been higher than the yield capacity of members under the geometries considered. So inelastic buckling is probable and has been investigated. By assuming the convergence point on the full diagonal member, the highest inelastic critical load is obtained. Hysteretic energy absorption of bracing increases by reducing the distance between convergence point and corner of frame. Hysteretic behavior of y-bracing becomes more symmetric in load-displacement coordinates with convergence point closer to the corner of frame.

With the increase of knowledge in seism city and subsequent need to modify the earthquake engineering design specification for buildings, it would be essential to investigate the behavior of such buildings and structures and the probable need for seismic retrofitting. On the other hand there are construction problems in strengthening and retrofitting methods using bracing system that reduces the owners wish to do so. In this paper an attempt has been made to investigate the behavior of existing building designed by second version of standard 2800 for seismic design of buildings and retrofitting of such structures using ADAS (Added Damping and Stiffness).For this purpose steel buildings are retrofitted once using bracing members alone and then using both bracing and ADAS dampers. The behavior of the steel frames was compared using non linear time history analysis. The behavior factor 'R' was calculated for each case. The assumed buildings had pinned jointed braced frames having different number of bays and stories. The results showed significant improvement in behavior of retrofitted frames with ADAS damper associated with lower content of steel. Comparisions indicated that negligible damage occurred in members of these frames and acceptable behavior was observed under earthquake loading. The members showed higher potential of withstanding sever earthquakes. Investigations have indicated a lack of information and design specification for structures with ADAS dampers.

The shape optimization of dams is a challenging and interesting task in Hydraulics Engineering. Due to this aim, the geometrical variables such as the bottom length, the slope of upstream and height of dams must satisfy both the stability criteria and economic considerations. Therefore, the shape optimization of dams can be interpreted as a constrained optimization problem whose main constraints are sliding stability, stability against overturning and normal stress in the surface of dams.In this paper, considering active forces on dams, such as weight, pressure, earthquake and uplift forces, the Genetic Algorithm approach has been used to optimize the shape of dam. Verifying the results with available recommendations shows the advantages and accuracy of this intelligent approach.In the next step by using Genetic Algorithm approach, 84 set of data were generated. These data are used as input for Artificial Neural Network. Then these data divided to two sets as training set and test set. By using a specific type of Artificial Neural Network (RBF) and a specific height of dam and earthquake acceleration, the bottom length and the slope of upstream were predicted. Results show that the R B F Network can be used for predicting the optimum shape of weight dams.

Weirs and gates are two types of hydraulic structures which are used in flow measurements in open channels. In irrigation networks, water flow from river is associated with sediment particles discharging into irrigation channels resulting in problems in performance of the designed system. Furthermore, in sediment flushing practices, water flow through these outlets, is associated with high sediment concentration which may effect the hydraulics of the flow. The available flow equations in determining discharge coefficients for weirs, orifices and gates are derived on the basis of laboratory tests under free-sediment flow conditions. In the present research, however, the effect of suspended sediment on discharge coefficients of flow through weirs and gates has been investigated experimentally. The test results indicate that there is remarkable difference between the discharge coefficients of the two hydraulic structures under sediment laden flow in comparison with clear water flow.

In this article the possibility of using Artificial Neural Networks for road detection from high resolution satellite images like IKONOS and Quick_Bird, is verified. Then, the influence of different input vectors on network’s functionality is evaluated to decide on optimum input vector. A variety of network structures are designed and each one is trained with different number of iterations to avoid over training problem. Accuracy assessment parameters are computed in each case to let us decide on the best network structure, optimum input vector and termination conditions for road detection purposes. Finally, results are compared with Maximum Likelihood classifier as the representative of statistical classification methods.