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Showing 9 results for Aghayari
Volume 4, Issue 2 (Summer 2020)
Abstract
The porosity of electrospun nanofibers web is a significant parameter affecting various areas of nanofibers applications. Thus, at first, the effect of most effective parameters, the concentration of polymer solution and flow rate, on the diameter of polyvinyl alcohol nanofibers, as a dissolving component, were investigated. Afterward, the hybrid web of polyamide 6/polyvinyl alcohol (PA/P) was prepared via a two-sided dual-nozzles electrospinning method. The morphology, diameter, pore size of nanofibers web and the effect of dissolving constituent were studied based on images of the scanning electron microscope. To measuring the porosity of nanofibrous webs, three practical and straightforward methods that have been proposed in the literature were utilized. It was observed that when one component was dissolved, the diameter of the resultant web was decreased, and the porosity has been reduced to about 70% based on the best selected method of porosity. Additionally, the average pore size of electrospun PA6 webs has been decreased about 30-58% relative to the original hybrid webs.
Volume 18, Issue 1 (Spring 2018 2018)
Abstract
The consumption pattern of typical household is a combination of quantities, qualities, acts and tendencies describing use of resources for survival, comfort and enjoyment by society or a group of people. In this paper, we examine the impact of cash subsidies on expenditure pattern of households after implementing Subsidy Targeting Project at both urban and rural levels in Iran. We estimate a panel data model by applying data on household income and expenditure survey (HIES) during 2004-2014. Findings indicates that paying cash subsidies significantly affects all 14 expenditure categories in urban and rural households, except for health expenditure in rural households. Consequently, the shares of eight urban expenditure categories and nine rural expenditure ones have increased, while the shares of six urban expenditure categories and four rural expenditure ones have decreased. In all cases except for home durable goods, the shares of urban and rural expenditure categories, the shares of other household expenses and transfers changed in a same direction. In both urban and rural levels, all increased shares of expenditure are related to current household’ welfare, but the shares of categories which increases future household’ welfare have decreased. It seems changes in relative prices after paying cash subsidies have persuaded households to sacrifice some investment, education, and health expenditure for additional expenditure required for meeting basic needs.
J. Aghayari, P. Safarpour, A. Rahi, S. Bab,
Volume 20, Issue 2 (February 2020)
Volume 20, Issue 2 (February 2020)
Abstract
In this paper, the application of passive vibrational linear absorber on the indirect reduction of blade vibrations using its mounted on the disk-blade system is studied. The absorber receives the vibration energy of blade through a structural coupling of the disk with blade and losses it by its linear damping. Due to cyclic symmetry, the analysis of the bladed disk is reduced to the number of DOFs in a single sector. A cyclic transformation from physical to modal coordinates is used to perform this reduction. Natural frequencies and forced responses of the system are obtained by solving the characteristic and algebraic equations, respectively. The case study of a steam turbine includes 259 blades in 37 packets of 7 connected blades attached to the perimeter of the disk. Cyclic symmetric finite element analysis at 3000rpm is used to extract the natural modes and frequency diagram of the system. A two DOFs reduced-order model is identified for modeling the frequency-veering region. This region has been formed between the first and second families of natural modes and there is a strong coupling between them in this region. In addition, this region is close to the system excitation line and the possibility of resonance exists. Therefore, some linear energy absorbers are mounted on the disk for the indirect vibration reduction of blades. The initial optimal parameters were determined for the first and second modes using Den Hartog relations. These parameters reduced the system vibrations and they were used in subsequent optimization. The optimization has resulted in the improvement of absorber performance exclusively around the second mode, in compare with the tuned system by Den Hartog relations.
M. Nozari, S. Tabejamaat, M. Aghayari, H. Sadeghzade,
Volume 20, Issue 7 (July 2020)
Volume 20, Issue 7 (July 2020)
Abstract
Combustion chamber has a crucial role in gas turbines and has a significant effect on the pollution and efficiency of them. Due to the complicated flow in combustion chambers because of high turbulence intensity, flow mixing, and flame behavior, prediction of the performance of such chambers is very complicated. There is a vital need for experimental investigations to study and understand the flame behavior in combustors. This experimental study was performed using a can type combustion chamber and LPG fuel at atmospheric conditions. First, stability curve, temperature distribution in the combustion chamber, and its exit plane in 6 flow conditions and then flow behavior were evaluated. The pollution at the outlet was obtained in different conditions and equivalence ratios. The results show that the flame tends to go downstream of the combustion chamber when the fuel mass flow rate increases (or in other words, by increasing the equivalence ratio) in constant air mass flow rate and finally exits from the chamber. By increasing the air mass flow rate in constant fuel mass flow rate, CO pollution is increased, and NOx pollution is decreased.
Volume 21, Issue 4 (Winter 2017)
Abstract
This research seeks to an analysis of mental indices effective on quality of life in rural areas and, therefore, current research is practical and in terms of research method, is a descriptive-analytical. Research population is rural households in Sinai District of Varzeghan County and sample size according to modified Cochran formula is 266 households. Main dimensions in the analysis of quality of life mental indices were examined in the framework of economic, social, health and physical dimensions tested by PLS in four stages. The results of the first stage show that, used indices have high reliability and validity. In the second stage in models structural test, according to T statistics about external relation among hidden variables, impacts of all indices are proved. In third stages and quality examining of measurement and structural models, calculated values are acceptable at the upper limit and in the result; assessment model has good quality. Finally, in the fourth stage, the general model of the structural test was considered. The GOF index of this model is estimated at 0.685, which is indicating the overall utility of the model. The existence of a positive and strong relationship between the measured indicators and the quality of life of the rural community show that health-social dimension, are key indices for measurement of quality of life in case study rural area
Majid Aghayari, Sadegh Tabejamaat,
Volume 22, Issue 7 (July 2022)
Volume 22, Issue 7 (July 2022)
Abstract
In the design of the combustion chamber, various parameters should be considered. These parameters include uniform temperature distribution at the outlet of the chamber, more flame stability, lower pollution, higher combustion efficiency, lower wall temperature, and lower pressure drop in the chamber. Regarding to the complex condition of the flow in the combustion chamber due to the various effects of turbulence and mixing of flows as well as the behavior of turbulent flames, predicting the performance of flow in the combustion chambers is very complicated. In this paper, it is tried to study and optimize the combustion chamber of Amirkabir University of Technology in terms of swirler. It is done by using the numerical method and finally the selected swirler in the numerical method is tested in the experimental setup to investigate optimization method .According to the studies, swirler with an angle of 60 degrees, 12 blades, and a thickness of 0.75 mm is selected as the final case. In the experimental results, the amount of CO pollution has significantly reduced. The output temperature, the pattern factor and unburned hydrocarbon have reduced in the final case. However, the temperature uniformity inside the chamber has increased.
Volume 23, Issue 3 (8-2023)
Abstract
The moment-resisting steel frame building is highly used due to their advantages such as, high speed construction coupled with appropriate strength and ductility. The main advantage of this system is related to architectural considerations and the possibility of creating openings within all spans. Connections play an outstanding role in the seismic responses of this structural system. The connections are generally assumed to have a rigid behavior in analyzing and designing of the moment-resisting steel buildings. Studying of the previous investigations indicates that the assumption of rigid behavior for the beam-to-column connections is not always correct and can bring about a significant error in the responses. In this study, behavior factor of moment-resisting steel frames considering joint flexibility is evaluated. To do so, some intermediate moment-resisting steel frames with various number of stories and bays including 1-bay, 1- and 2-story frames, 2-bay, 2-, 4-, 6-, 8-, and 10-story frames, 3-bay, 3-, 6-, 9-, and 12-story frames and 4-story, 2-, 6-, 10-, and 14-story frames are designed regarding Iranian seismic code and Iranian national building code for designing steel structures. After that, the capacity curves of these frames are achieved using pushover analysis once considering rigid connections and again taking joint flexibility into consideration using OpenSees software. To model the nonlinear behavior of connections, one zero-length rotational spring is assigned to each end of beam members. Then, the behavior factor of each frame is calculated using the recommended procedure of FEMA-P695. The outcomes show that for the frames with rigid connections, the acquired behavior factors are almost close to 5 (which is the prescribed behavior factor in Iranian seismic code for the intermediate moment-resisting steel frames). Furthermore, for the frames with semi-rigid connections (60%), the behavior factors are close to 5 as well. For 10-story 2-bay, 12-story 3-bay, and 14-story 4-bay frames the prescribed behavior factor in Iranian seismic code does not meet. For these frames, the ratio of height to total-span that is known as the slenderness coefficient of the frame is higher than others, so these frames fall into slender frames. Results show that for the frames with semi-rigid connections (60%), despite of decreasing the over-strength factors in some cases, their ductility increased, therefore, the behavior factors are achieved higher than those of the frames with rigid connections. All in all, it is observed that the nonlinear behavior of connections can significantly affect the seismic behavior of the moment-resisting steel frames. Comparing the behavior factors calculated in this investigation with the prescribed value of this factor in code 2800 showed that for the frames with rigid connections, 80% of the obtained behavior factors are higher than 5. For frames with semi-rigid connections (80% and 60%), 0%, and 66% of the behavior factors meet the proposed value of code 2800, respectively. Regarding the observations, it is recommended that the influence of joint flexibility be considered in assigning a value of behavior factor to design the moment-resisting steel frames.
Keywords: rigid connections, semi-rigid connections, moment-resisting steel frame, nonlinear static analysis, distributed and concentrated plasticity models
Volume 23, Issue 4 (10-2023)
Abstract
Surrounding the central core of a concrete component by means of an internal or external factor such as transverse reinforcements, carbon and polymer fibers and steel sheets causes confinement for the concrete. Confining generally improves the strength and ductility of concrete components. As a result of boosting the local performance of elements, the overall performance of structure is made progress. Recently, tending to build irregular structures has been increasing. The presence of irregularity in the structure has always been one of the challenges faced by engineers. In this investigation, the influence of confinement phenomenon on the seismic performance (damage level and behavior factor) of the moment resisting reinforced concrete frames with vertical irregularity is assessed. To do so, 31 moment resisting frames with vertical irregularity are categorized in four classes including 3-, 6-, 9- and 12-story and the roof displacement-base shear curves of them are acquired using pushover analysis. The capacity curve of each frame is achieved in two states including neglecting the confinement effect and considering it. The outcomes indicate that not only can confining improve the seismic performance of structures but also it can decrease the imposed damage of structures. In other words, comparing the capacity curves of each frame with/without confining effect shows that taking the confinement effect leads to improving the secant stiffness and strength of the frame. Furthermore, due to confinement effect, lateral load carrying capacities of the frames are boosted and the considered damage levels are achieved in higher base shear and roof displacements in comparison with the state that confinement is not considered. The observed values of damage levels indicate that the influence of confinement for higher frames is more significant and the maximum base shears for the frames with the confining action is around 3-19% higher than those of the frames without confinement effect. For 3-story frames, considering confinement effect leads to improving 3.9, 3.6 and 2.9% in damage levels of DL, SD, and NC. For 6-story frames these values are 6.9, 9.5, and 6.8% respectively. Taking confinement effect results in improving 18.25, 11.8, and 14.6% in damage levels of DL, SD, and NC and 14.3, 14.2, and 13.3% improvement for 12-story frames. Comparing the behavior factors in the two states demonstrates that considering confining effect improves the mean values of behavior factors around 10.4%. In addition, the observed values of behavior factors show that the differences between the amounts of behavior factors (with/without confinement effect) for the frames with more stories are higher. It is manifested that type of irregularity plays significant role on the seismic behavior of the moment-resisting reinforced concrete frames. Comparing the analytical behavior factor obtained in the current study with the prescribed value of behavior factor in Iranian seismic code shows that although the proposed value of Iranian seismic code is conservative for low-rise frames, this value is not met for high-rise frames.
Volume 26, Issue 1 (Spring 2022)
Abstract
Introduction
Lack of essential services increases the need for mobility and relocation in rural areas and makes people travel to meet their needs. The need for mobility along with the absence of public transportation services, while prolonging travels, has affected travel demand and flow, so that people use several vehicles in a travel chain (origin-destination) (Stfen and Hunt, 2006: 104). Various spatial factors affect the flow, destination and volume of trips, which can be shown by spatial analysis and modeling as one typical method to do this. Spatial statistics tools include a set of techniques and methods for describing and modeling spatial data. Use of spatial statistics helps us to increase the accuracy of results and observations in cases where the distribution or dispersion of data in space is complicated. In this paper, geographically-weighted regression and spatial modeling have been used to show the volume and travel flow in villages, and also the factors affecting them to determine, besides the origin and destination of rural travels, travel volume and their spatial distribution. The question is what factors are influential in the destination of these trips and their volume, and to what extent is the impact of each of these factors on the frequency of rural travel demands.
Methodology
The present article is a descriptive-analytical method with a practical purpose and the data is collected both in the field and from the existing documents. In the documentary section, some data were collected from 1390 and 1395 censuses and some other using questionnaires. The statistical population of the study were all rural households in Tabriz County, where a researcher-made questionnaire was used to obtain travel information. Since the number of households amounted to 33379 families, using the Cochran formula 320 sample sizes were selected and questionnaires were randomly distributed between rural households. Given that the primary purpose of this study is to model the spatial pattern of passenger flow in space and time, so that the spatio-temporal mobility of passengers in the road network can be seen, three components including the extraction of passenger travel pattern (Origin-destination), determination of the travel routes, and the factors affecting these trips were identified. In the first step, the data obtained from the questionnaire were processed to model and plot the travel pattern (origin-destination of trips). For this purpose, it was necessary to identify the villages with and without bus stations and public transportation servicesas well as the travel routes of passengers. The next step is modeling the travel patterns and flow of passengers. In this study, ArcGIS software was used to show the flow of travel. This mapshows the direction of movement and the volume of the flow adjusted by line widths. Using the simulated travel routes, a flow matrix was obtained from the travel volume among all villages, small towns, and Tabriz city. Then, to investigate the dominant pattern of the travel demand, spatial autocorrelation analysis (local Moran pattern) and hot spots were used to determine the pattern of space travel distribution. Finally, in order to reveal the most influential factor affecting travel demand as the independent variable, a geographically-weighted regression model was formed and the relationship between travel and such indicators as demographic, economic, and social factors were analyzed and modeled.
Results and discussion
Initially, the data collected from the villages were entered into the ArcGIS software to obtain the origins and destinations of the passengers, their travel directions, and the way their travels were distributed. Then, using Spatial analyst tools, the direction and spatial distribution of trips were obtained by a straight line as an Origion-Destination matrix for short-term trips to Tabriz city. The results showed that many trips were made outside the countryside to the city of Tabriz, and some of these trips were made to large villages and small towns. According to the data extracted from the questionnaire, many of these trips are made by car or taxi because many of these villages are on the roads where public transport does not pass through.
Hot spot analysis has been used to identify villages with high travel rates. The results obtained from the analysis of hot spots indicate that the main places of travels are mostly in the villages of Maidan Chai and Aji-Chay, which seems to be due to the access to public transportation services and the existence of villages with buses to Tabriz city in these rural areas. In the next step, in order to model and explain the effect of research variables on travel demand, GWR was used in GIS. According to the results of the analysis, the parameters of R2 and adjusted R2 are 0.8 and 0.75, respectively. This means that based on a geographically-weighted regression, the indicators considered at the 0.95 confidence level explain 0.80 of the trips and have acceptable accuracy in modeling the spatial relationships of the factors affecting the travel demands of individuals. In addition, the AICc value indicates a lower number, indicating a better fit of the observed data. Due to the different nature of the indicators, the effect of each of the indicators and factors on the amount of travels was investigated separately. The results show that the highest amount of R2 with a value of 0.72 is related to the access to the public transport, followed by the number of workers outside the village with a value of 0.70. Among these, the least influential factor is the total travel time to reach the destination with a value of 0.21, which indicates that people travel to access services and meet their needs regardless of the total time to reach their destinations.
Conclusion
The results of the study showed that several factors have affected the heterogeneity of travel demands in rural areas, which, according to the study, access to the public transport and people working outside the village have the most impact. In addition, most of daily trips to the city of Tabriz are done for business and by personal cars. These trips are based on hot spot analysis in Maidan Chai and Ajichay villages, where most of the villages near the city of Tabriz have access to the public transport (bus) and taxi. The short distance between these villages and the city of Tabriz, the existence of public transportation services in them, and consequently lower costs and ease of movement have caused the accommodation of the overflow of Tabriz in these villages and have increased the demand for travel in these villages, in such a way that during the day, the movement of travelers in these villages is the same as daily trips in the city of Tabriz, and educational, recreational, shopping, health, etc. trips are made from these villages to the city of Tabriz. In addition, the presence of several industrial towns and factories near the villages of Ajichai and Maidanchai has increased the number of business trips in these villages.
Lack of essential services increases the need for mobility and relocation in rural areas and makes people travel to meet their needs. The need for mobility along with the absence of public transportation services, while prolonging travels, has affected travel demand and flow, so that people use several vehicles in a travel chain (origin-destination) (Stfen and Hunt, 2006: 104). Various spatial factors affect the flow, destination and volume of trips, which can be shown by spatial analysis and modeling as one typical method to do this. Spatial statistics tools include a set of techniques and methods for describing and modeling spatial data. Use of spatial statistics helps us to increase the accuracy of results and observations in cases where the distribution or dispersion of data in space is complicated. In this paper, geographically-weighted regression and spatial modeling have been used to show the volume and travel flow in villages, and also the factors affecting them to determine, besides the origin and destination of rural travels, travel volume and their spatial distribution. The question is what factors are influential in the destination of these trips and their volume, and to what extent is the impact of each of these factors on the frequency of rural travel demands.
Methodology
The present article is a descriptive-analytical method with a practical purpose and the data is collected both in the field and from the existing documents. In the documentary section, some data were collected from 1390 and 1395 censuses and some other using questionnaires. The statistical population of the study were all rural households in Tabriz County, where a researcher-made questionnaire was used to obtain travel information. Since the number of households amounted to 33379 families, using the Cochran formula 320 sample sizes were selected and questionnaires were randomly distributed between rural households. Given that the primary purpose of this study is to model the spatial pattern of passenger flow in space and time, so that the spatio-temporal mobility of passengers in the road network can be seen, three components including the extraction of passenger travel pattern (Origin-destination), determination of the travel routes, and the factors affecting these trips were identified. In the first step, the data obtained from the questionnaire were processed to model and plot the travel pattern (origin-destination of trips). For this purpose, it was necessary to identify the villages with and without bus stations and public transportation servicesas well as the travel routes of passengers. The next step is modeling the travel patterns and flow of passengers. In this study, ArcGIS software was used to show the flow of travel. This mapshows the direction of movement and the volume of the flow adjusted by line widths. Using the simulated travel routes, a flow matrix was obtained from the travel volume among all villages, small towns, and Tabriz city. Then, to investigate the dominant pattern of the travel demand, spatial autocorrelation analysis (local Moran pattern) and hot spots were used to determine the pattern of space travel distribution. Finally, in order to reveal the most influential factor affecting travel demand as the independent variable, a geographically-weighted regression model was formed and the relationship between travel and such indicators as demographic, economic, and social factors were analyzed and modeled.
Results and discussion
Initially, the data collected from the villages were entered into the ArcGIS software to obtain the origins and destinations of the passengers, their travel directions, and the way their travels were distributed. Then, using Spatial analyst tools, the direction and spatial distribution of trips were obtained by a straight line as an Origion-Destination matrix for short-term trips to Tabriz city. The results showed that many trips were made outside the countryside to the city of Tabriz, and some of these trips were made to large villages and small towns. According to the data extracted from the questionnaire, many of these trips are made by car or taxi because many of these villages are on the roads where public transport does not pass through.
Hot spot analysis has been used to identify villages with high travel rates. The results obtained from the analysis of hot spots indicate that the main places of travels are mostly in the villages of Maidan Chai and Aji-Chay, which seems to be due to the access to public transportation services and the existence of villages with buses to Tabriz city in these rural areas. In the next step, in order to model and explain the effect of research variables on travel demand, GWR was used in GIS. According to the results of the analysis, the parameters of R2 and adjusted R2 are 0.8 and 0.75, respectively. This means that based on a geographically-weighted regression, the indicators considered at the 0.95 confidence level explain 0.80 of the trips and have acceptable accuracy in modeling the spatial relationships of the factors affecting the travel demands of individuals. In addition, the AICc value indicates a lower number, indicating a better fit of the observed data. Due to the different nature of the indicators, the effect of each of the indicators and factors on the amount of travels was investigated separately. The results show that the highest amount of R2 with a value of 0.72 is related to the access to the public transport, followed by the number of workers outside the village with a value of 0.70. Among these, the least influential factor is the total travel time to reach the destination with a value of 0.21, which indicates that people travel to access services and meet their needs regardless of the total time to reach their destinations.
Conclusion
The results of the study showed that several factors have affected the heterogeneity of travel demands in rural areas, which, according to the study, access to the public transport and people working outside the village have the most impact. In addition, most of daily trips to the city of Tabriz are done for business and by personal cars. These trips are based on hot spot analysis in Maidan Chai and Ajichay villages, where most of the villages near the city of Tabriz have access to the public transport (bus) and taxi. The short distance between these villages and the city of Tabriz, the existence of public transportation services in them, and consequently lower costs and ease of movement have caused the accommodation of the overflow of Tabriz in these villages and have increased the demand for travel in these villages, in such a way that during the day, the movement of travelers in these villages is the same as daily trips in the city of Tabriz, and educational, recreational, shopping, health, etc. trips are made from these villages to the city of Tabriz. In addition, the presence of several industrial towns and factories near the villages of Ajichai and Maidanchai has increased the number of business trips in these villages.
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