Showing 12 results for Olyaei
Volume 3, Issue 3 (12-2014)
Abstract
The effects of pyrene on gill, liver and kidney of common carp (Cyprinus carpio) were examined by exposing 30 fish (140 ±10 g to pyrene at sublethal concentrations of 10, 50 and 100 µg/l for 35 days. Samples were taken from the organs and fixed in bouin fixative; then, dehydrated, cleared, parafinated and cut by microtome according to the standard method. Afterwards, all sections were studied by light microscope. In gill tissue, lamella hyperemia, hyperplasia, S shaped, and clubbing were observed, while lamella fusion and necrosis were observed in higher concentration of pyrene. Hepatocytes vacculation, congestion of sinusoids, macrophages loaded with hemosiderin were seen in the liver, while in higher concentrations of pyrene, picnotic and kariolized nuclei, and tissue necrosis were seen. Tubule casts, hyperemia, degenerating tubules were seen in kidney exposed to lower concentrations of pyrene, while hemosiderin-laden macrophages, degenerating tubules with greater intensity as well as necrosis was observed in higher concentrations. The results indicated that pyrene may have negative effects on homeostasis, fish health and vital organs in short time exposure due to histological changes, while it could have greater impacts in long term exposure and higher concentrations.
Volume 8, Issue 4 (3-2019)
Abstract
design of two phrase mathematical model for green supply chain Green supply chain has attracted considerable attention of the governments and organizations over the past decades. The objective of this research is to suggest an integrated approach for green supply chain management including two stages. In the first stage, a TOPSIS-Fuzzy approach was presented to consider uncertainty in human’s judgment. In the second stage, we applied a robust Multi Objective Mixed-Integer linear Programming model to design the green supply chain network. Although many researches have been conducted on green supply chain management, most of them have not given enough importance to integrate decision making in supply chain. Moreover, most of former researches assume that supply chain is a balanced system. Also very few studies have considered carbon emission and the related issues in supplier evaluation which cause on overall warming and pollution of the planet. The model was designed for an active company in glass industry. results have revealed that the model is capable of controlling the network uncertainties.
Volume 12, Issue 4 (11-2012)
Abstract
Soldier pile consists of the passive reinforcement (i.e., no post-tensioning) of existing ground by installing closely spaced steel bars (i.e., nails), which are subsequently encased in grout and transfer the loads from steel piles to soil. As construction proceeds from the top to bottom, concrete is also applied on the excavation face to provide continuity. Soldier pile is typically used to stabilize excavations adjustment to the buildings to prevent surface movement and cracks in the buildings where top-to-bottom construction is advantageous compared to other retaining wall systems. For certain conditions, soldier pile offers a viable alternative from the viewpoint of technical feasibility, construction costs, and construction duration when compared to ground anchor walls, which is another popular top-to bottom retaining system.
This paper addresses soil nails that are installed with a near horizontal orientation and are primarily subjected to tensile stresses together steel piles which act as cantilever beam with horizontal nails as supports. Soldier pile can be used for both temporary and permanent structures based on its service life or intended duration of use.
Soldier pile is a form of ground retention used when ground conditions comprise of dense to moderately dense soils such as coarse grain alluviums. Soldier pile systems with lateral nails are used in many excavation projects. This method is one of the appropriate support systems in deep excavations. However, most of the researches have been focused on the effects of wall height on the stability of excavations in static conditions, but with increasing of the use of soldier pile systems in seismic regions, the dynamic stability of these structures cannot be ignored. According to increasing of the usage of the soldier pile systems in seismic active zones, it’s important to study the dynamic behavior of these structures. Hence, in this paper, the seismic behavior of soldier pile systems in Tehran coarse grain alluvium has been investigated. The methodology is based on pseudo-static approach to equalize the dynamic analysis. The numerical modelings have been done according to Finite Difference Method (FDM) to this equalization.
Based on slope stability theory, it has been shown that the pseudo-static method is a suitable and simple approach to equalize dynamic behavior. Therefore, in this paper, a similar approach has been used to equalize dynamic behavior of soldier pile systems with considering a proposed pseudo-static coefficient. The failure surfaces in dynamic and pseudo-static
models efficiency. Network of this case study is the roads network of Fars province that it has 59 nodes and 80 arcs. Two groups of hazardous materials are considered and the risk factor is calculated for each group in all links. Each node can be the potential point of the demand or a point of supply. All paths can be used in both directions, and it has been assumed that the risk of passing hazardous material through the path between two nodes is equal for both directions. Risk index includes three factors, “population under effect”, “the environment assets”, and “the number and importance of road facilities across a link”. Results showed the best possible and the safest and most economical routes, would be obtained by solving the safety model and using the result of this model in the safety-economic model.
Volume 14, Issue 5 (especial summer- 2014)
Abstract
Lateral ground displacement due to liquefaction causing damages to major infrastructures like buildings, bridges, pipe, shore line utilities etc. When the surface slope is mild, a common mode of failure is lateral spreading with surface displacements that can exceed several meters. Considering the widespread use of pile foundations, their safety in the occurrence of earthquake has a special importance. Studies after the earthquake have shown that both the force due to structure and the Kinematics interaction between the pile foundations and the soil play an important role in mechanical behavior of piles. Since the effect of the superstructure on the pile-soil interaction analysis is significant; the analysis should be done based on the interaction axis of pile-soil-structure. In this study, finite difference method (FDM) has been used to investigate the effect of the thickness of liquefied layer, slope of liquefied layers and the underground water level on behavior of pile foundations. Results indicate that with an increase in the slope of liquefied layers, the maximum bending moment raises but the slope of this graph for low underground water level (near the surface) is higher. This type of behavior also is observed in the shear force created in the pile foundation.
Eiman Bondar Saheby, Ghader Olyaei, Azadeh Kebriaee,
Volume 16, Issue 11 (1-2017)
Abstract
Integration of airframe and propulsion system is one of the most challenging steps in flight vehicle design cycles. In this paper, a three-dimensional supersonic inlet based on the wave-derived geometry technique has been designed and analyzed. Although the considered method was created for hypersonic forbodies, the idea is fully operational for the low supersonic inlet design at Mach 1.6. The inlet concept in this paper is formed from predefined profile elements which are used to generate the three-dimensional geometry in an oblique shock pattern. By this approach, the curved corner of the inlet entrance edge can generate the same shock as the main compression surface and also these curved surfaces provide the optimum transition between entrance geometry and compressor face which is important for the airflow quality and propulsive efficiency. The new concept has been validated by a series of accurate CFD simulations with completely structural grid domains. The major inlet's performance factors like total pressure recovery, flow distortion and mass flow capture ratio are calculated. The concept and it's accurate numerical simulations create a baseline for more advanced designs and researches about the three-dimensional inlets and geometry transition techniques between the different sections of duct.
Eman Bandar Saheby, Ghader Olyaei, Azadeh Kebriaee,
Volume 17, Issue 4 (6-2017)
Abstract
Planar inlet concepts play an important role in the design of supersonic propulsion systems. The inlet reduces the speed of supersonic flow by the oblique shock wave or an array of oblique shock waves and a final normal shock provides the subsonic flow after the throat of the diffuser. In this paper, a design method of Mach 3.0 supersonic multi-ramp inlet is explained, the geometry is designed and simulated by the numerical solver. Designing the inlets for the high supersonic Mach range, between 3 and 5 is very challenging because of the viscosity interactions and the related effects on the propulsive efficiency. The considered inlet in this study is a mixed system which provides the required compression by the combination of the three external ramps and a subsonic diffuser. A computational code calculated the optimum dimensions numerically and a second order CFD solver has simulated the inlet operations by the accuracy of 10E-05. In addition to aerodynamic performance, Advantages and problems of such a combination, development of boundary layer and its interactions with the normal shock and performance of bleeding mechanism are simulated and studied. Finally, this paper presents compact details of design, simulation and viscosity effect of mixed compression surface.
Eiman Bondar Saheby, Ghader Olyaei, Azadeh Kebriaee, Guoping Huang,
Volume 17, Issue 10 (1-2018)
Abstract
In this paper, a hypersonic inlet for operating at Mach 5.0 is designed and analyzed numerically. The main axis of this study is a series of three-dimensional simulations with the accuracy of 10E-06 which are applied to determine the effects of the highly developed boundary layer on the performance of inlet for three different study cases. The basic inlet concept is designed by integration of double ramp compression surface and inlet duct which can reduce the free-stream Mach number to the range of 2.0. The most important factor that it affects the performance of the hypersonic inlet system, is the developed entropy layer on the fuselage of the flight vehicle. Ingestion of this layer results in thermal gradients and pressure recovery losses. The bow shocks at the nose and the leading edges are the main sources of this low kinetic energy layer. Using the k-ω turbulence model in the numerical simulations have resulted in a reliable estimation of the boundary layer. In the current context, shock structures, shock-boundary layer interactions, flow quality at the end of the diffuser and also the effects of using sidewalls on the performance of the hypersonic inlet are the main goals of the simulations and the related results are summarized
Gh. Olyaei, A. Kebriaee ,
Volume 19, Issue 4 (April 2019)
Abstract
The present study was performed to experimentally investigate the regime of the liquid sheet breakup and the effects of dimensionless numbers on the penetration and trajectory of the liquid sheet in cross flow condition. The shadowgraphy technique was applied to study the tests. In this work, the effect of the non-dimensional numbers (momentum ratio and Weber number) were surveyed on the breakup of the liquid sheet. Also, some equations for the injection trajectory, the length, and the height of the jet were presented based on these non-dimensional numbers. The tests were done at atmospheric pressure and temperature, where the Weber number range is from 0.8 to 12.5, the variations of the momentum ratio are from 17.4 to 250, and the changes in the Reynolds number are from 2400 to 10227. Three regimes of jet breakup were observed, defined as column breakup, column-bag breakup, and bag breakup. The Weber number is the most effective parameter in the regime change of the liquid sheet breakup. The results also indicated that the increase in the momentum ratio has a great influence on the depth of penetration of the liquid sheet, but it has a very small effect on the breakup regimes.
Volume 19, Issue 5 (12-2019)
Abstract
Drought is an integral part of natural hazards. It usually occurs gradually and without any warning. Moreover, this phenomenon is usually created over time and does not disappear quickly Recently, some factors such as climate variability and the impact of climate change have influenced drought frequency and intensity in many parts of the world. Various definitions have been provided for drought but in general the lack of water resources in a specific period in a geographical area is considered as drought which implies this phenomenon as a regional hazard. IRAN is located in an arid and semi-arid region in which it experiences drought frequently. There are different types of drought such as meteorological, hydrological, agricultural and social-economic. These types are differentiated based on the factor which is rainfall, river flows, soil moisture, and social-economic consequences. There are many indices proposed for measuring drought severity; among them Standardized Precipitation Index (SPI), Palmer Drought Severity Index (PDSI) and Surface Water Supply Index (SWSI) could be mentioned. Each of these indices has its own pros and cons and is suitable for a particular type of drought. Therefore knowing the types of drought can provide a better understanding of shortages and their characteristics. Various factors are utilized for measuring these indices including precipitation, reservoir storage, discharge, temperature and potential evapotranspiration. In this study the three main aforementioned indices were first calculated for Aharchay watershed, located in East Azerbaijan province. Next based on combining these three indices with another two important parameters, groundwater level and solar radiation, a combined drought index is developed and calculated for the studied region. Considering the fact that the aforementioned parameters and indices have different level of importance in combined index, different weights based on expert opinions are assigned to the parameters considering how critical each parameter is in the overall drought analysis. This combined index demonstrated various climatic, hydrological and agricultural aspect of the region. In the next step, bivariate analysis of the two variables, intensity and duration, is carried out using copula. This is done by first checking the dependency between intensity and duration using Pearson, Spearman, and Kendall correlation coefficients. Second, various copula functions were fitted such as Gaussian, T, Clayton and Gumbel functions. Third, based on the Ordinary Least Square (OLS) and Kolmogorov–Smirnov (K-S) tests, the best copula functions were used. Lastly, based on the chosen copula the joint probability distributions were obtained. Two cases named “OR” and “AND” were defined for joint probability of the two variables and different return period curves is drawn. The results showed that the most severe drought in this watershed occurred in June 2004. Moreover, by assessing correlation coefficient between the considered indices it is shown that analysis of the drought in a region based solely on one index would neglect other imperative aspects in drought determination which necessitates a more integrated indicator. Furthermore, in bivariate analysis, return periods of “AND” cases were more than “OR” case. The results of this study could be utilized in preparedness and monitoring drought.
Volume 20, Issue 1 (3-2016)
Abstract
Today's world is more competitive than ever, and industry increasingly looks to supply chain management as a competitive weapon. the objective of this research is to suggest an integrated approach for Closed Loop Supply Chain network including two phases. In the first phase, a framework for supplier selection criteria in RL is proposed. Beside a fuzzy method is utilized to evaluate suppliers based on quantitative and qualitative criteria. The output of this stage is the weight of each supplier according to each part.in the second phase, we propose a Multi Objctive mixd-integer linear programming model to determine weight of suppliers and amount of item for purching from them(strategic decisions), as well as weight of remanufacturing subcontractor and dedicate product to them (tactical decisions), and find out the optimal number of part and products in CLSC network(operational decisions). The objective functions maximize profit of selling, minimize factory cost as well as cost of unsatisfied demand and rest of them maximize weight of suppliers and allocate return product between recoverable centers in factory and remanufacturing subcontractors. the mathematical programming model is validated through numerical analysis.
Volume 20, Issue 4 (11-2020)
Abstract
Abstract:
Pullout resistance of cement-grouted soil nails is a key factor affecting the safety conditions of retaining walls, slopes and excavations. Hence, survey of resistence of pullout nail is the one of the most important parameters in designing of nailing functions. This parameter depend on critical factors including: instalation method, overburden press, grouting pressure, degree of saturation of the soil, the roughness of nail surface, changes of lengh & diameter of nail, the shear strengh of the soil and etc.
Sometimes, used soil nail layers affected by cyclic loads due of traffic passing, train and so on. Hence the research aimed to study influence of this kind loadings on resistence of nail post-cyclic pullout and affective factors on it. The study pointed to apply slopes and nailed retaining walls next to traffic loads and rail-roads. Several studies conducted; according to, vary factors influence on nail pullout behavior that buried into soil. Key studies carried out in form of impression of static loading on nail pullout resistance including: overburden stress, grouting stress, impression of an addition to grouting, nail geometry, nail spaces, using spiral nails, comparison laboratory results of pullout set with direct shear test in interface grouted-nail to earn identical ratio and etc. yet, it not examineted cyclic loading impression on post-cyclic pullout resistance in nails. The study just focus on geogrid. For the first time, this research provide impression of cyclic loading on post-cyclic pullout resistance in nails.
This research used nail pullout set; able to apply static and cyclic loads in conditions of force or displacement controling with differ frequencies and sinus shape of cyclic wave. This search used the notes of specifications of pullout set; also, sampling due to test and tables of done tests. In this research examined affection of variation of static, cyclic load rate. Resistance of post-cyclic pullout nail generally is more to static pullout resistance; even though , more affections of cyclic loading lead to decrease of resistance; also, obserued in the cyclic part developing in displacement.
Key words : pullout resistance , soil nail , post-cyclic , static and cyclic load
Volume 20, Issue 5 (11-2020)
Abstract
In recent decades, the use of an efficient and cost-effective method to provide soil stability has been a major challenge for civil engineers. With increasing urban population, the need for underground spaces increases and deep excavation is an inevitable affair in civil projects. Deep tunnels and large buildings require deep excavations, which must use some techniques for stabilize it. Soil-nailing (reinforcing soil at the site) due to the fast build, is a good way to provide stability. It can also be described as a top-down construction technique for the improvement of behavioural properties of in-situ soil mass. Soil-nailed system is formed by inserting relatively slender reinforcing bars into the slope. Depending upon the project cost, site accessibility, availability of working space, and the soil and groundwater conditions, soil-nails can be inserted into the ground. Soil-nail is generally known as conventional and injectable nails but nails with screw plates or "helical soil-nails" are also important due to the faster build and no need for groutings. Helical soil-nails are new alternative to the conventional soil nails or tie-backs for stabilization of slopes, excavations and embankments due to ease of installation, minimal site disturbance and immediate loading capability. Helical soil-nails are installed by application of torque without a drill hole and derive its capacity from one or more helical plates attached to the nail. The shear strength-displacement behavior at the interface is an important parameter in design of various geotechnical engineering projects, for example, soil-nails, retaining walls, shallow foundations, pile foundations, etc. In soil-nailing, behavioure of interface between the soil and nail estimated by pull-out test. The behaviour of interface is governed by numerous factors, such as stress conditions, soil properties, method of installation and soil-nail interface boundary conditions. The pull-out resistance is measured as the most important factor in the design of the nailing system, by pull-out test. This study, because of limited learning of helical soil nail, aimed to investigate the pull-out resistance by a 3D finite element modeling with abaqus software and compare its results with laboratory data. A review of the literature for the screw soil-nails as well as a comparison of its performance with conventional soil nails is discussed and numerical results of a series of pull-out tests on a screw soil-nail are presented. And review of the overburden pressure and plate number and plate distance effect is followed. The results show that in helical soil-nail pull-out a high overburden pressure effect can be seen. A semi-linear relationship between peak pull-out force and overburden pressure is observed for different methods of calculating the helical soil-nail capacity that it is indicating that it satisfies the Mohr-Coulomb failure criteria. Rupture surfaces occur at distances farther than the nail surface, and three times the diameter can be considered the optimal distance of the plates. Using fewer plate distance does not increase resistance, also using more plate with fewer distance does not increase resistance. Comparison of modeling and laboratory results indicates that modeling of pull-out test can model the behavior of helical soil-nail and verify its performance in a field soil slope.