Loading...
Search for:
hemati-nik--javad
0.12 seconds
Total 232 records
Optimal Design of Tolerances in the Non-rigid Assemblies under the Thermal Impact
, M.Sc. Thesis Sharif University of Technology ; Khodaygan, Saeed (Supervisor)
Abstract
Tolerance allocation in the recent mechanical assembly is significant because it straightly affects product performance and cost. Loose tolerances may cause the quality defect while tight tolerances can increase the cost. Thermal effects and the temperature gradients are one of the factors that caused changes in the size and geometry of the components during the performance of mechanical assemblies. This thesis proposes a new approach for tolerance design considering the thermal effects, to achieve lower manufacturing cost and good product quality. Finite element analysis is used to determine the deformation of components in an assembly. The neural network is trained using experimental...
, M.Sc. Thesis Sharif University of Technology ; Akbari, Javad (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
In conventional grinding of hard to cut materials such as Ti6Al4V alloys, surface burning, redeposition and adhesion of chips to wheel and workpeice occur visibly unless it is carried out at low speeds and with high volume of cutting fluid. Ultrasonic assisted grinding (UAG) is an efficient machining process for hard-to-cut materials with poor machinability. UAG improves the machinability of such materials by changing the kinematics of the process. In this research, the effect of imposition of ultrasonic vibration on the grinding of Ti6Al4V is studied. Longitudinal vibration at ultrasonic frequency range (20 kHz) is applied on the workpiece and machining forces and surface roughness are...
Water allocation using game theory under climate change impact (Case study: Zarinehrood)
, Article Journal of Water and Climate Change ; Volume 12, Issue 3 , 2021 , Pages 759-771 ; 20402244 (ISSN) ; Abrishamchi, A ; Sharif University of Technology
IWA Publishing
2021
Abstract
The combined effects of climate change and growing water demand due to population growth, industrial and agricultural developments cause an increase in water scarcity and the subsequent environmental crisis in river basins, which results in conflicts over the property rights and allocation agreements. Thus, an integrated, sustainable and efficient water allocation considering changes in water resources due to climate change and change of users’ demands is necessary. In this study, the drainage basin of Zarinehrood was chosen to evaluate the function of selective methods. Assessing climate change impact scenarios of the Fifth IPCC reports, e.g., RCP2.6, RCP4.5, RCP6.0 and RCP8.5, have been...
General Review of the Gamma Irradiators for the Purpose of Desing Improvement of Multipurpose Systems
, M.Sc. Thesis Sharif University of Technology ; Sohrabpour, Mostafa (Supervisor)
Abstract
Ionizing radiation can modify physical, chemical and biological properties of the irradiated materials. At present, the principal industrial applications of radiation are sterilization of health care products including pharmaceuticals, irradiation of food and agriculture products and materials modification. In the above application the wide range of the required doses together with different product densities require spatial mechanical design of the irradiators to be able to properly handle the specified tasks. In the multipurpose irradiators the design of system and positioning of the source must be done in such a way that a nearly optimum dose distaition in the product boxes in...
An analytical investigation of elastic-plastic deformation of FGM hollow rotors under a high centrifugal effect
, Article International Journal of Mechanical and Materials Engineering ; Volume 14, Issue 1 , 2019 ; 18230334 (ISSN) ; Aghajani, S ; Hemati, M ; Sharif University of Technology
Springer
2019
Abstract
Functionally graded material shafts are the main part of many modern rotary machines such as turbines and electric motors. The purpose of this study is to present an analytical solution of the elastic-plastic deformation of functionally graded material hollow rotor under a high centrifugal effect and finally determine the maximum allowed angular velocity of a hollow functionally graded material rotating shaft. Introducing non-dimensional parameters, the equilibrium equation has been analytically solved. The results for variable material properties are compared with the homogeneous rotor and the case in which Young’s modulus is the only variable while density and yield stress are considered...
History Modeling in Conversational Question Answering
, M.Sc. Thesis Sharif University of Technology ; Beigy, Hamid (Supervisor)
Abstract
In this thesis, we propose a method for long document modeling to address the issue of handling lengthy documents. The results indicate that our method successfully improves the problem of independently modeling chunks that arise from long documents. Additionally, we present consistent training using history augmentation to enhance the representation of questions with a long history. Our experiments demonstrate that this proposed method increases the performance of the baseline model, particularly for questions with a long history. The long document modeling approach improves the baseline's performance by 2.1% based on the F1 criteria. Furthermore, the consistent training using history...
Preparation and Physico-chemical Characterization of Titanium Dioxide Nanotubes with Electrochemical Method for Oxidative Dehydrogenation of Propane (ODHP)
, M.Sc. Thesis Sharif University of Technology ; Kazemeini, mohammad (Supervisor)
Abstract
Samples of the V2O5 catalysts supported on nanostructures of TiO2 and γ-Al2O3 were synthesized via hydrothermal method for the oxidative dehydrogenation of propane (ODHP) to propylene. The TiO2 support was utilized in both commercial microstructures and prepared nanostructures from their corresponding salts. Furthermore,the γ-Al2O3 was also prepared from two novel methods. Moreover, the vanadium catalysts supported on hybrid TiO2 and γ-Al2O3 were prepared. The performances of the prepared catalysts were subsequently examined in a fixed-bed reactor. The main products were propylene, ethylene and COx.The vanadium catalyst over TiO2 and γ-Al2O3 had the best performance under the reactor test...
Theoretical study of CO adsorption on the illuminated TiO2 (0 0 1) surface
, Article Applied Surface Science ; Volume 256, Issue 12 , 2010 , Pages 3795-3798 ; 01694332 (ISSN) ; Sadighi Bonabi, R ; Sharif University of Technology
2010
Abstract
A quantum modeling of the CO adsorption on illuminated anatase TiO2 (0 0 1) is presented. The calculated adsorption energy and geometries of illuminated case are compared with the ground state case. The calculations were achieved by using DFT formalism and the BH and HLYP. Upon photoexcitation, an electron-hole pair is generated. Comparing of natural population in the ground state and the exited state, shows that an electron is trapped in a Ti4+ ion and a hole is localized in an oxygen ion. The photoelectron helps generation of a CO2 molecule on the TiO2 surface. As shown by optimization of these systems, the CO molecule adsorbed vertically on the TiO2 (0 0 1) surface in the ground state...
Coordinated Scheduling of Power and Natural Gas Systems Considering Demand Uncertainty
, M.Sc. Thesis Sharif University of Technology ; Rafiee, Majid (Supervisor)
Abstract
The everyday increasing electricity consumption of household and industrial sectors across the world, and also the limited generation capacity and fuel supplies has led electricity companies, whether in private or government sectors, to focus deliberately on power generation planning, its costs, risks and constraints Because of many reasons including high efficiency, low cost of capital investment, expeditious permitting, and operation flexibility of gas-fired generating units, electricity companies prefer them to old ones like coal-fired or oil-fired generating units. Thus natural gas has gained a significant share in the portfolio of electricity generation fuel resources, and it is...
Numerical Investigation of the Effect of Influential Geometrical Parameters on the Plugholing Phenomenon in Smoke Extraction
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor)
Abstract
Correct and timely extraction of smoke is very important in fire incidents. Statistics show that more than seventy percent of fire casualties are caused by breathing toxic gases. One of the destructive factors in the operation of the smoke exhaust system is the plugholing phenomenon. In this phenomenon, due to the improper design of the ventilation system, the exhaust vent extracts air instead of smoke. The plugholing phenomenon causes the accumulation of smoke in the structure, therefore it is essential to know this phenomenon to prevent it. In this research, the plugholing phenomenon in the smoke extraction process has been investigated by the numerical simulation method. To investigate...
A bi-objective aggregate production planning problem with learning effect and machine deterioration: modeling and solution
, Article Computers and Operations Research ; Volume 91 , March , 2018 , Pages 21-36 ; 03050548 (ISSN) ; Akhavan Niaki, S. T ; Hemati, M ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
The learning effects of the workers and machine deterioration in an aggregate production planning (APP) problem have not been taken into account in the literature yet. These factors affect the performance of any real-world production system and require attention. In this paper, a bi-objective optimization model is developed for an APP problem with labor learning effect and machine deterioration. The first objective of this model maximizes the profit by improving learning and reducing the failure cost of the system. The second objective function minimizes the costs associated with repairs and deterioration, which depend on the failure rate of the machines in the production periods. The aim of...
Conflict Resolution of water resources Allocation Using Game Theory under Climate Change Impact (Case Study: Zarinehrood basin)
, M.Sc. Thesis Sharif University of Technology ; Abrishamchi, Ahmad (Supervisor) ; Tajrishi, Masoud (Co-Supervisor)
Abstract
Increasing water consumption via competitive demands has resulted in serious water conflicts and the subsequent environmental crisis in river basins. The combined effects of climate change on river flow and growing water demand due to population growth, industrial and agricultural developments cause an increase of water scarcity in many basins. This is one of the drivers of both noncompliance with water allocation agreements and conflicts over the property rights to river water. Conflicts often arise when different water users compete for a limited water supply. Thus an integrated, sustainable, efficient and fair water allocation considering changes in water resources due to climate change...
Decision Matrix for Time-Critical Optimal Trajectories for Air-Launch of Small Satellites
, M.Sc. Thesis Sharif University of Technology ; Malaek, Mohammad Bagher (Supervisor)
Abstract
One of the satellite time-critical launch methods is air-launch, which is considered in this research thoroughly. The Large number of important parameters of this method makes the system highly complex. In such complex systems, usual methods of design and development will not be effective. Moreover, based on systemic approaches, interfaces between different elements of a complex system have significant effects on the performance of the whole system. One of the methods for analysis of such systems is “Design Structure Matrix” or DSM. This method is based on system engineering principles and has confirmed capabilities in analysis of highly coupled systems.
In this research, the air launch...
In this research, the air launch...
Effect of Soil-Structure Interaction on Practical Design of Ordinary Buildings Based on Iranian Seismic Code
, M.Sc. Thesis Sharif University of Technology ; Ghannad, Mohammad Ali (Supervisor)
Abstract
In the last few decades Seismic Regulations attitude’s has been undergone significant changes from various aspects. One of these aspects is entering new topics based on the latest scientific achievements. Soil-Structure Interaction terms was from such issues which had found their ways into Seismic codes as an optional effective factor. In recent years, Based on this new attitude and Scientific achievements, Soil-Structure Interaction terms entrance into Iranian seismic code (2800 Standard), is also has been studied. Naturally, applying these criteria will impact on the design and performance of structures, because of reducing effect of soil structure interaction on decreasing base shear...
Ultrasonic-assisted grinding of Ti6Al4V alloy
, Article Procedia CIRP ; Volume 1, Issue 1 , 2012 , Pages 353-358 ; 22128271 (ISSN) ; Movahhedy, M. R ; Akbari, J ; Sharif University of Technology
2012
Abstract
In conventional grinding of hard to cut materials such as Ti6Al4V alloys, surface burning, redeposition and adhesion of chips to the grinding wheel and workpeice occur visibly unless it is carried out at low speeds and with high volume of cutting fluid. Ultrasonic assisted grinding is an efficient machining process which improves the machinability of hard-to-cut materials by changing the kinematics of the process. In this research, the effect of imposition of ultrasonic vibration on the grinding of Ti6Al4V alloy is studied. Longitudinal vibration at ultrasonic frequency range (20 kHz) is applied on the workpiece and machining forces and surface roughness are compared between conventional...
Identification of Self-Leadership Strategies of Social Entrepreneurs in Face of Challenges of their Career
, M.Sc. Thesis Sharif University of Technology ; Alavi, Babak (Supervisor) ; Tasavori, Misagh (Supervisor)
Abstract
The present study seeks to focus on social entrepreneurs to address how these entrepreneurs continue to have sufficient motivation to overcome the challenges they face in the course of their careers and continue this path. This research has tried to use the concept of self-leadership - which keeps a person motivated to achieve his goals for which he has an inner motivation - to answer this question. So the main research question is how do social entrepreneurs use their leadership in the face of the challenges of their careers? To answer this question, this study used a qualitative research method with an exploratory approach and conducted semi-structured interviews with 14 social...
A fuzzy random minimum cost network flow programming problem [electronic resource]
, Article Journal of Industrial and Systems Engineering (JISE)-Iranian Institute of Industrial Engineering ; Article 3, Volume 6, Issue 1, Spring 2012, Page 34-47 ; Eshghi, Kourosh ; Sharif University of Technology
Abstract
In this paper, a fuzzy random minimum cost flow problem is presented. In this problem, cost parameters and decision variables are fuzzy random variables and fuzzy numbers respectively. The object of the problem is to find optimal flows of a capacitated network. Then, two algorithms are developed to solve the problem based on Er-expected value of fuzzy random variables and chance-constrained programming. Furthermore, the results of two algorithms will be compared. An illustrative example is also provided to clarify the concept
Special classes of mathematical programming models with fuzzy random variables [electronic resource]
, Article Journal of Intelligent and Fuzzy Systems, Published In: IOS Press ; Volume 19, Number 2, 2008 ; Nematian, Javad ; Sharif University of Technology
Abstract
In this paper, we will discuss two special classes of mathematical programming models with fuzzy random variables. In the first model, a linear programming problem with fuzzy decision variables and fuzzy random coefficients is introduced. Then an algorithm is developed to solve the model based on fuzzy optimization method and fuzzy ranking method. In the second model, a fuzzy random quadratic spanning tree problem is presented. Then the proposed problem is formulated and solved by using the scalar expected value of fuzzy random variables. Furthermore, illustrative numerical examples are also given to clarify the methods discussed in this paper
A special class of fuzzy integer programming model with all different constraints [electronic resource]
, Article Scientia Iranica ; Vol. 16, No. 1, pp. 1-10, 2009 ; Nematian, Javad ; Sharif University Of Technology
Abstract
In this paper, a fuzzy approach is applied to special classes of integer programming problems with all diierent constraints. In the rst model, a fuzzy integer programming model is developed to represent the all-diierent constraints in mathematical programming. In order to solve the proposed model, a new branching scheme for the Branch and Bound algorithm is also presented. In the second model, a special class of large-scale multi-objective fuzzy integer programming problems with all-diierent constraints is introduced. A solution method for the proposed model is also developed by using the decomposition technique, weighting method and Branch and Bound algorithm. An illustrative numerical...
Fuzzy random minimum cost network problem [electronic resource]
, Article Journal of Industrial and Systems Engineering ; Vol. 6, No. 1, pp 34-47, 2012 ; Eshghi, Kourosh ; Sharif University of Technology
Abstract
In this paper, a fuzzy random minimum cost flow problem is presented. In this problem, cost parameters and decision variables are fuzzy random variables and fuzzy numbers respectively. The object of the problem is to find optimal flows of a capacitated network. Then, two algorithms are developed to solve the problem based on Er-expected value of fuzzy random variables and chance-constrained programming. Furthermore, the results of two algorithms will be compared. An illustrative example is also provided to clarify the concept