Saeed Bahrami - Academia.edu (original) (raw)

Papers by Saeed Bahrami

Single-shaft gas turbine and its cycles are sensitive to frequency drops and, therefore, sudden c... more Single-shaft gas turbine and its cycles are sensitive to frequency drops and, therefore, sudden change loads or large frequency dips might affect their stability. This phenomenon is related to the reduction of the air mass flow passing through the machine during the frequency dips, which might lead to an interaction between governor and temperature control loop. In this paper, the performance of the combined cycle and steam-injected gas turbine are studied during frequency dips and transient maneuvers. For this purpose, two similar units are developed based on these cycles and their performances are studied in different scenarios. The simulation results show that the steam injected gas turbine has a better performance during frequency drops and it can handle relatively larger change loads.

Periódico Tchê Química, 2020

Corylus avellana L., common hazelnut, is a globally cultivated economically valuable nut crop tre... more Corylus avellana L., common hazelnut, is a globally cultivated economically valuable nut crop tree with a sensitivity to abiotic stresses remarkably low temperature. Its intensity varies based on the growth and developmental stage. The commercial consequences of cold stress on nut setting of hazelnuts are significant and practical approaches to address the problem are highly demanded. To tackle the issue of cold stress intolerance in C. avellana and provide producers with practical solutions, this study aimed to investigate the effects of various chemical substances on ten years old C. avellana trees under cold stress and its responses at the physiological and biochemical levels in leaves and female and male flowers. Hazelnut trees were treated with salicylic acid (3 mg L-1), potassium (2 mg L-1), thiofer (5 mg L-1), biobloom (66 mg L-1), and amino acid (0.5 mg L-1) in different treatments using the foliar spray under an average temperature of 4.13°C. It could be observed that the e...

An Integrated of Fuzzy Rule Base System and TOPSIS Technique for Multi-Attribute Decision Making

Proceedings of the 3rd International Conference on Software Engineering and Information Management, 2020

Multi-attribute decision making (MADM) is one of important issues in make-decision have been cond... more Multi-attribute decision making (MADM) is one of important issues in make-decision have been conducted many research in recent years. Indeed, the main objective of this research is developing an extended Fuzzy rule based method based on TOPSIS conventional technique. This paper aids to solve a MADM problem by means of fuzzy environment under a group decision making. To do so, fuzzy rule based system (FRBS) is used to obtain final score of alternatives toward each individual expert's opinions. And also, TOPSIS technique is used in order to final aggregation of expert's results and makes a unique decision. This study makes an investigation on data about a supplier selection problem (SSP) as a case-based problem has been taken from a valid research. Robustness and validity of the proposed method is indicated with a numerical example, and compare the output of results with another validated approach.

Civil engineering infrastructures journal, 2019

Precast concrete structures in Iran are generally designed as continuous columns with hinged beam... more Precast concrete structures in Iran are generally designed as continuous columns with hinged beams, thereby making them simple frames. In this system in site show walls in two directions of buildings guaranteed lateral resisting system. However, in order to obtain a seismic resisting frame, the connection between beam and column should be moment resisting and ductile, allowing the formation of plastic hinges at these connections as well as at the column base. In this paper, experimental tests were conducted for precast concrete elements with modified beam-column connection under cyclic load. The precast connection considered for this study was a semi precast beam with welded longitudinal bars to embedded plate into beam where the beam is connected to corbel with welding embedded plated to plate on the corbel. According to the results, the connection shows suitable performance until drift of 2.75% in terms of stiffness, damping and moment resistance.

SOUTHERN BRAZILIAN JOURNAL OF CHEMISTRY, 2020

In many low-temperature areas, the environmental factor is an important limiting factor for the p... more In many low-temperature areas, the environmental factor is an important limiting factor for the production and distribution of horticultural plants. This study aimed to investigate the cold tolerance of the male catkins and inoculated female flowers to screen the popular native hazelnut cultivars in Qazvin under low-temperature stress. A completely randomized factorial block design with three replications was used in this experiment with eight cultivars (Nakhnroud, Khandan, Mish-Pestan, South of Qarabagh, Asl-e-Qarabagh, Rasmi, and Gerdashkevar). After removing each of the treated samples at the end of the experiment, the samples were examined morphologically (appearance) and compared with the control. The changes were recorded as qualitative traits. To understand the influence of cold stress on reproductive organs, hydrogen peroxide and proline were measured. The results showed the onset of freezing in unopened male catkins at -7 and -9 °C and in inoculated female flowers at -3 °C....

Examining the relationship between growth and value stock and liquidity in Tehran Stock Exchange World of Sciences Journal

●● ● In every financial market there are various tools to be used in investment depending on mark... more ●● ● In every financial market there are various tools to be used in investment depending on market size and depth. Asset liquidity in a main issue in investment since some investors may require their financial resources. Liquidity rate is related to investors' enthusiasm to perform transactions in the Stock Exchange. The present paper examines relationship between growth and value stocks and liquidity in Tehran Stock Exchange in a 10-year period (2002-2011). It uses three transactional standards (transaction mass, transaction frequency and stock turnover rate) to determine liquidity standard. Data pertaining to the time series are gathered annually and examined by Eviews Software through panel data method. In order to achieve a better examination of relationship between the two variables "size" and "financial leverage" enter into the model as control variables. Results demonstrate a negative, significant relationship between growth stock and liquidity and la...

Study of Iran Khodro auto industry as the largest country in terms of entrepreneurial orientation... more Study of Iran Khodro auto industry as the largest country in terms of entrepreneurial orientation and organizational assessment has studied. Population study of 3742 people, experts and managers of middle and senior managers of Iran Khodro organizations were using proportional stratified sampling method and the Cochran formula samples were 187 cases. The data collected standardized questionnaire (Lumpkin and Dess, 2005, p. 153) was. Face validity questionnaire obtaining expert opinions Vastadan organizational entrepreneurship Tehran University were studied reform was necessary. Questionnaire reliability was estimated by Cronbach's alpha coefficient value for the different parts of the questionnaire was higher than 0.8. Open to answer questions through research, semi-structured interviews with industry experts, the data combined with the findings of literature research and knowing the market, the industry was attempting to provide solutions for the institutional development of en...

Variable fill fluid couplings are used in the speed control units. Also, variation in coupling oi... more Variable fill fluid couplings are used in the speed control units. Also, variation in coupling oil volume is used in adapting one size of coupling to a wider range of power transmission applications. Available model for the partially filled fluid couplings, has a good performance for couplings with fixed amount of oil but their performance will be degraded if they are used for the variable fill couplings. In this paper, the current model for partially filled fluid couplings is modified to have better performance for variable fill couplings. For this purpose, the circulation loss calculation is modified and also, the effect of oil temperature variations and blade thickness are included in the model. The effect of these modification on the model performance are investigated in couple of simulations. Comparing the simulation results with the available experimental data shows that the suggested modifications can improve the model performance very well.

Clinical Hemorheology and Microcirculation, 2020

Cardiovascular disease is now under the influence of several factors that encourage researchers t... more Cardiovascular disease is now under the influence of several factors that encourage researchers to investigate the flow of these vessels. Oscillation influences the blood circulation in the volume of red blood cells (RBC) strongly. Therefore, in this study, its effects have been considered on hemodynamic parameters in the elastic wall and coronary bifurcation. In this study, a 3D geometry of non-Newtonian and pulsatile blood circulation is considered in the left coronary artery bifurcation. The Casson model with various hematocrits is analyzed in elastic and rigid walls. The wall shear stress (WSS) cannot show the stenosis artery alone, therefore, the oscillatory shear index (OSI) is represented as a hemodynamic parameter of WSS individually of time. The results are determined using two-way fluid-structure interaction (FSI) coupling method using an arbitrary Lagrangian-Eulerian method. The most prominent difference in velocity happened in the bifurcation and at hematocrit 30 with yi...

Biomechanics and Modeling in Mechanobiology, 2018

In this study, a three-dimensional analysis of the non-Newtonian blood flow was carried out in th... more In this study, a three-dimensional analysis of the non-Newtonian blood flow was carried out in the left coronary bifurcation. The Casson model and hyperelastic and rigid models were used as the constitutive equation for blood flow and vessel wall model, respectively. Physiological conditions were considered first normal and then compliant with hypertension disease with the aim of evaluating hemodynamic parameters and a better understanding of the onset and progression of atherosclerosis plaques in the coronary artery bifurcation. Two-way fluid-structure interaction method applying a fully implicit second-order backward Euler differencing scheme has been used which is performed in the commercial code ANSYS and ANSYS CFX (version 15.0). When artery deformations and blood pressure are associated, arbitrary Lagrangian-Eulerian formulation is employed to calculate the artery domain response using the temporal blood response. As a result of bifurcation, noticeable velocity reduction and backflow formation decrease shear stress and made it oscillatory at the starting point of the LCx branch which caused the shear stress to be less than 1 and 2 Pa in the LCx and the LAD branches, respectively. Oscillatory shear index (OSI) as a hemodynamic parameter represents the increase in residence time and oscillatory wall shear stress. Because of using the ideal 3D geometry and realistic physiological conditions, the values obtained for shear stress are more accurate than the previous studies. Comparing the results of this study with previous clinical investigations shows that the regions with low wall shear stress less than 1.20 Pa and with high OSI value more than 0.3 are in more potential risk to the atherosclerosis plaque development, especially in the posterior after the bifurcation.

Applied Mathematical Modelling, 2018

 Spectral element method was developed for vibration analysis of circular and annular circular p... more  Spectral element method was developed for vibration analysis of circular and annular circular plates.  A novel formulation was developed for dynamic analysis of circular and annular circular plates.  Circular annular displacement subjected to impact load was calculated.

Applied Mathematical Modelling, 2017

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  Spectral element method was developed for vibration analysis of shallow shells.  The effect of in-plane boundary conditions of shallow shells was discussed.  Shallow shell displacement subjected to impact load was calculated.

Engineering Structures, 2017

In this study, two new moment resisting connections of beams to precast concrete columns under la... more In this study, two new moment resisting connections of beams to precast concrete columns under lateral load were analyzed via application of nonlinear finite element analysis software ABAQUS 6.10. The precast connections considered were the beam-column connections in which precast beams is connected to continuous precast column with corbel using (i) inverted E (bolted connection) and (ii) box section (welded connection). Connection responses associated with lateral resistance, lateral stiffness, ductility, and energy dissipation were compared to a reference monolithic connection. Achieved lateral resistance, lateral stiffness and ductility of the proposed connections was approximately 98%, 80% and 80% of the equivalent monolithic connection, respectively. The effect of axial load on column and compressive strength of concrete on behavior of the connections were studied. The analytical results show that the performance of two proposed precast connections were close to the performance of corresponding monolithic connection.

Environmental Earth Sciences, 2017

A simple one-dimensional analytical solution is presented to model oxygen diffusion through the p... more A simple one-dimensional analytical solution is presented to model oxygen diffusion through the pore space of mine spoils containing pyrite. The model incorporates volumetric oxygen consumption terms due to pyrite oxidation, oxidation of Fe 2? to Fe 3? and bacterial activity. Based on this analytical solution, a graphical user interface (GUI) tool is programmed and designed in MATLAB software. This tool can be used to model transport of oxygen through the mine spoils either with or without a cap. Results of several simulation scenarios of sensitivity analysis showed a significant change in oxygen concentration with varying effective diffusion coefficient of oxygen transport model and simulation time. Efficiency and flexibility of the tool developed here is verified by modelling oxygen transport through the pore space of a coal waste pile (case A) and a copper mine tailings (case B). Maximum depth of oxygen diffusion is obtained approximately equal to 2 and 1.5 m through the cases A and B, respectively.

International Journal of Physical Sciences, Apr 4, 2011

In the real time database management systems the mechanism of concurrency control 2PL-high priori... more In the real time database management systems the mechanism of concurrency control 2PL-high priority, by applying a sacrificing approach of the low-priority transaction during the competition with high priority transaction, not only waste the resources of the system but also decrease the system efficiency due to the increase of the transaction failure because of miss deadline. The survey is focusing on the weak points of this mechanism and presenting a new approach that by omitting the unnecessary restarts greatly improve the efficiency of the system. We also present a new approach for determining the transaction's priority to provide the possibility of more successful transaction. This approach will be more prominent especially when there is more competition among the transactions for locking the resources of the system. By modeling the behavior system in Markov model, this increase in efficiency of the system comparing to the 2PL-HP mechanism has been improved.

Energies, 2015

Genetic algorithms for finding optimal locations of mobile agents in scalable active networks

2011 2nd International Conference on Artificial Intelligence, Management Science and Electronic Commerce (AIMSEC), 2011

... Fatemeh Torgheh M.Sc of Engineering Software Computer, Technical Department, Abhar Branch, Is... more ... Fatemeh Torgheh M.Sc of Engineering Software Computer, Technical Department, Abhar Branch, Islamic Azad University. ... Where: n = total number of vertices in the graph, ai = demand of vertex i, dij = distance from vertex i to vertex j , p = number of facilities used as medians, ai ...

Advances in Multimedia, 2012

Security of the multimedia data including image and video is one of the basic requirements for th... more Security of the multimedia data including image and video is one of the basic requirements for the telecommunications and computer networks. In this paper, we consider a simple and lightweight stream encryption algorithm for image encryption, and a series of tests are performed to confirm suitability of the described encryption algorithm. These tests include visual test, histogram analysis, information entropy, encryption quality, correlation analysis, differential analysis, and performance analysis. Based on this analysis, it can be concluded that the present algorithm in comparison to A5/1 and W7 stream ciphers has the same security level, is better in terms of the speed of performance, and is used for real-time applications.

Applied Mathematical Modelling, 2015

A spectral strip method (SSM) in frequency domain was developed to analyze annular Levy-type plat... more A spectral strip method (SSM) in frequency domain was developed to analyze annular Levy-type plates subjected to impact loads. The dynamic formulation was developed for an annular sector plate with simple boundary conditions on radial edges and any boundary conditions on circular edges with constant and variable thickness. Using Bessel's equations, modified Bessel's equations, and separation of variation technique, the dynamic differential equation of annular sector plate in frequency domain is solved. Numerical results show the accuracy of this method in comparison to other numerical methods using less number of elements (strip).

A dynamic model was developed for long-term simulation of a heavy duty gas turbine. The model inc... more A dynamic model was developed for long-term simulation of a heavy duty gas turbine. The model includes the essential control algorithm of the gas turbine as well as the most common outputs and other important intermediate variables. Control algorithm details, such as wind up protection and load limiter algorithm which have large effect on gas turbine transient behavior, are included. The model parameters are identified by applying genetic algorithm and least squares algorithm on regular operational data from a real plant to better match the model response to the real plant. The simulation results have been validated with real plant data and shown to have valid accuracy for many engineering applications.