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jiryaei-sharahi--hassan
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Strengthening and ductilization mechanisms of friction stir processed cast Mg–Al–Zn alloy
, Article Materials Science and Engineering A ; Volume 781 , 2020 ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
AZ91 alloy, the most widely used Mg casting alloy, exhibits low strength/ductility and weak energy absorption, which is a function of its large grain size and the presence of a coarse and continuous network of β-Mg17Al12 intermetallic compounds. This work demonstrated that friction stir processing (FSP) enables enhancement of strength and energy absorption capability of AZ91 alloy. The influence of FSP treatment on various potential strengthening mechanisms, including grain boundary, solid solution, and sub-micron particle strengthening mechanisms, was studied. It is identified that the grain boundary strengthening plays a significant contribution to the strength of the FSP treated AZ91. FSP...
Pre-weld friction stir processing enabling strong and ductile fusion welds on AZ91 magnesium alloy
, Article Science and Technology of Welding and Joining ; Volume 28, Issue 2 , 2023 , Pages 162-171 ; 13621718 (ISSN) ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Taylor and Francis Ltd
2023
Abstract
Liquation in the partially melted zone (PMZ) is the critical weldability issue of cast AZ91 magnesium alloy. Friction stir processing (FSP) is used as a local pre-weld treatment to create a local liquation-resistant microstructure in cast AZ91 alloy during arc welding. The effects of tool rotational speed during pre-weld FSP on the liquation-related microstructural features (i.e. grain structure, size and volume fraction of eutectic β-Mg17Al12) and the liquation characteristics of the fusion-welded AZ91 (i.e. PMZ size and grain boundary liquid film thickness) were investigated. The pre-weld FSP treatment of the cast AZ91 significantly improved the tensile strength and ductility of the welds...
Investigation on the Effect of Friction Stir Processing on the Fusion Weldability of Magnesium Alloys
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor) ; Movahedi, Mojtaba (Supervisor)
Abstract
Magnesium alloys, as the lightest structural alloys having a density of about one-fourth that of steels, offer significant potential for improving the energy efficiency of various transportation systems. Welding is a critical enabling manufacturing technology; therefore, the widespread application of a material is highly influenced by their weldability. Liquation and Liquation cracking are crucial weldability issues for fusion welding of cast AZ91 Mg alloy. The constitutional liquation of the coarse eutectic Mg17Al12 intermetallic phase is responsible for the occurrence of liquation cracking during fusion welding of this alloy. Here, friction stir processing (FSP) treatment, a successful...
Effect of collision on self-assembly of nanoparticles in zirconia microparticle suspension
, Article Journal of Dispersion Science and Technology ; 2020 ; Saidi, M. H ; Sharif University of Technology
Bellwether Publishing, Ltd
2020
Abstract
Nanoparticle halo mechanism is a stabilization method for microparticle suspensions. This study investigates suspension pH and nanoparticles–microparticles collision effects on the stabilization of an aqueous binary suspension. The long-term turbidity measurements show that for the nanosilica suspension stability is directly correlated with pH values; however, in the cases of zirconia and binary suspensions, it is not a monotonic function of pH. It is shown that for binary suspension, the halo mechanism is the primary method affecting the stability of the suspension. The suspension is best-stabilized at pH = 5 that is associated with high halo mechanism efficiency, while increased repulsive...
Effect of collision on self-assembly of nanoparticles in zirconia microparticle suspension
, Article Journal of Dispersion Science and Technology ; Volume 43, Issue 6 , 2022 , Pages 787-795 ; 01932691 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
Nanoparticle halo mechanism is a stabilization method for microparticle suspensions. This study investigates suspension pH and nanoparticles–microparticles collision effects on the stabilization of an aqueous binary suspension. The long-term turbidity measurements show that for the nanosilica suspension stability is directly correlated with pH values; however, in the cases of zirconia and binary suspensions, it is not a monotonic function of pH. It is shown that for binary suspension, the halo mechanism is the primary method affecting the stability of the suspension. The suspension is best-stabilized at pH = 5 that is associated with high halo mechanism efficiency, while increased repulsive...
Enhanced resistance to liquation cracking during fusion welding of cast magnesium alloys: Microstructure tailoring via friction stir processing pre-weld treatment
, Article Materials Science and Engineering A ; Volume 798 , 2020 ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Magnesium alloys provide critical opportunities for energy and lightweight-materials challenges. The alloy design approach based on utilizing the second phase strengthening mechanism plays an essential role in producing low-density high strength Mg-based alloys. However, the second phase in the microstructure (e.g., Mg17Al12 phase in Mg–Al–Zn alloys) can deleteriously affect the weldability of the metallic materials by promoting the liquation and liquation cracking during fusion welding. The lack of sufficient weldability of Mg-based alloys is a crucial barrier to their potential use in safety-critical applications. In this paper, it is shown that the severe plastic deformation induced by...
Effect of liquation on the tensile properties of cast Mg–9Al–1Zn Alloy fusion welds
, Article Science and Technology of Welding and Joining ; Volume 25, Issue 8 , 2020 , Pages 698-705 ; Jiryaei Sharahi, H ; Movahedi, M ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
This paper aims at understanding the role of liquation and solidification phenomena on the tensile properties of arc welded cast AZ91 magnesium alloy. Owing to its refined microstructure, the fusion zone exhibited improved ductility/strength compared to the base metal. It is demonstrated that the partially melted zone (PMZ) which is characterised by constitutional liquation of eutectic β-Mg17Al12 phase is the weakest link in the weldment. The reduced strength and ductility associated with the liquation phenomena are due to the increased volume fraction and thickness of the eutectic β-Mg17Al12 in the PMZ as well as the formation of liquation micro-cracks in a network of brittle intermetallic...
Translation Surfaces With Constant Mean Curvature or Gauss Curvature in 3-Dimensional Spaces
, M.Sc. Thesis Sharif University of Technology ; Fanaii, Hamid Reza (Supervisor)
Abstract
In Euclidean space R3 , a surface is called a translation surface if it is given by an immersion X : U 2 Rn ! Rn+1 : (x1; :::; xn) ! (x1; :::; xn; f1(x1) + ::: + fn(xn)) where fi; i = 1; ::; n are smooth functions.In this work, we give the classification of translation surfaces with constant mean curvature or Gauss curvature in 3-dimentional Euclidean space R3 and 3-dimentional Minkowski space L3 and We also characterize the minimal surfaces in the upper half-space model of 3-dimentional hyperbolic space H3 and we express this contents for spaces with arbitrary dimentional too
Structural Design of a Launch Vehicle with Reusable First Stage
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor)
Abstract
Aerodynamics loads and aeroheating during reentry, are one of the challenging issues in designing One of the main challenges in the design and application of reusable spacecrafts is the aerodynamic and thermal loads acting on their structures during reentry into the atmosphere. For this reason, all the concepts/prototypes presented in the 20th century were either not fully reusable, or were partially canceled, or did not have economic justification. In this report, the aerodynamic loads on the first stage of a launch vehicle during the launch and return phases have been investigated. Due to the fact that the main part of the first stage of the vehicle includes fuel and oxidizer tanks, the...
Optimal Trajectory Correction for Hazardous Near-Earth Asteroids
,
M.Sc. Thesis
Sharif University of Technology
;
Zohoor, Hassan
(Supervisor)
;
Sayyadi, Hassan
(Supervisor)
Abstract
The collision of moderately large asteroids and comets also referred to as Near-Earth Objects (NEO's) with earth would have catastrophic consequences. Such events have occurred in the past and may occur again in the future. However, for the first time in known history, humanity may have the technology required to counter this threat. Methods studied for mitigation of this hazard are based on deflecting asteroid's trajectory and are normally divided into two basic categories: high energy impulsive methods, and long-duration low-thrust methods. Two parts of mission to be optimized are the trajectory of spacecraft to reach the target and the deflection strategy which could be analyzed by the...
A revised version of ACO for cutting stock problem [electronic resource]
, Article International Journal of Industrial Engineering ; Vol 15, No 4 (2008), Pages 341-348 ; Javanshir, Hassan ; Sharif University of Technology
Abstract
The one-dimensional cutting stock problem has many applications in industries and during the past few years has been one of the centers of attention among the researchers in the field of applied operations research. In this paper, a revised version of Ant Colony Optimization (ACO) technique is presented to solve this problem. This paper is a sequel to the previous ACO algorithm presented by the authors. In this algorithm, according to some probabilistic rules, artificial ants will select cutting patterns and generate a feasible solution. Computational results show the high efficiency and accuracy of the proposed algorithm for solving one- dimensional cutting stock problem
Control of Car-Like Multi Robots for Following and Hunting of Moving Target
, M.Sc. Thesis Sharif University of Technology ; Sayyaadi, Hassan (Supervisor) ; Salarieh, Hassan (Co-Advisor)
Abstract
The main purpose of the present thesis is to establish a decentralized controller for some car–like multi robots to follow and hunt moving targets. Robots are very similar to actual cars considering geometric dimensions, mass and moment of inertia and so on; and outputs of the controller are steering-wheel and driving-wheel torques appropriately. Dynamics of the moving target is so that it escapes from the robots. Robots are equipped with antenna for getting wireless sensory signals, including range and bearing sensors. Kalman filter is used for estimation the target relative position and speed and robots state variables. The controller is designed for doing the above mentioned group...
Stock Price Forecasting Using Neural Networks and Fuzzy Logic
,
M.Sc. Thesis
Sharif University of Technology
;
Shavandi, Hassan
(Supervisor)
Abstract
This research proposes a novel hybrid method for stock price index forecasting relying on technical analysis, the fundamental analysis of capital market, neural networks technology, and fuzzy logic. The new method shows a good performance comparing complicated and time-consuming forecasting methods. Several factors influence stock price; for example, an important one is the previous trend of stock price. Fortunately, by developing technical analysis and introducing the various indices of this method the maximum use of historical data is made in order to forecast future prices. Another kind of factors is macro-economic variables that their influence on the long-term trends of the stock...
Control of a Group of Mobile Manipulators for Cooperative object Transportation
, M.Sc. Thesis Sharif University of Technology ; Sayyadi, Hassan (Supervisor)
Abstract
In this thesis control of wheeled mobile manipulators for cooperative object transportation is investigated. Full dynamic model of a mobile manipulator with a three wheeled mobile base and a three DOF manipulator is derived using Gibbs-Appell method. Input-output linearization technique is used to control individual robots. Transporting the object is divided into two steps, first robots use a decentralized behavior-based method to approach and surround the object. Then virtual structure method is used to control the robots to transport the object cooperatively. Simulation results with three robots handling an object are presented to show the effectiveness of proposed method
Dynamic and Control of Tethered Satellite Systems
,
M.Sc. Thesis
Sharif University of Technology
;
Salarieh, Hassan
(Supervisor)
Abstract
In this work dynamic behavior of a two body TSS with main satellite as rigid body is studied and effects of tether elasticity and tension on the satellite dynamic are indicated in station keeping phase and circular orbit. Also a simplified modeling is introduced which could be used in nonlinear controller design. Lagrange and extended Lagrange method is used to derive equations of motion. It is shown that longitudinal vibration of tether has small effect on satellite attitude and angular velocity and because of high frequency it can be decoupled from satellite dynamic. In the simplified model, orbital motion is decoupled from equations of TSS and main satellite dynamic. Effect of decoupling...
Analysis of Control of Nonlinear Switched Systems
, M.Sc. Thesis Sharif University of Technology ; Zohoor, Hassan (Supervisor)
Abstract
Separate analysis of modern systems by continuous or discrete theories is not possible, because they cannot solely express the detailed descriptions of a system. As a result of this, researchers are motivated to study hybrid systems. Specific class of hybrid systems which consists of several continuous subsystems and a rule that specifies how to switch between them, is called a switched system. Recently, many studies have been done on the stability and control of switched systems. In this regard, the goal of present study is presenting applications of switched systems using two control methods. The first application is control of a chemical reactor system with multiple modes. We presented...
Design and Analysis of a Cable Based Robot Similar to a Human Hand
, M.Sc. Thesis Sharif University of Technology ; Zohoor, Hassan (Supervisor)
Abstract
The application of manipulators is becoming more and more popular in objects handling especially when it is desired to have access to remote areas in destructive or hazardous taskspaces. For this purpose, a hand-like mechanism must be designed to be used as an end-effector, which can grasp objects. In this paper a cable driven grasping mechanism has been presented. In the proposed mechanism each finger consists of three phalanxes which are actuated by a single motor. Also, locking and unlocking constraints are used in the mechanism in order to generate an anthropomorphic motion, in which, the order of reaching phalanxes to the object is sequential, in such a way that each phalanx starts...
Data Integration with Multiple Ontologies in Semantic Sensor Web
, M.Sc. Thesis Sharif University of Technology ; Abolhassani, Hassan (Supervisor)
Abstract
Sensor Observation Service (SOS) which is defined by Open Geospatial Consortium (OGC) Sensor Web Enablement group is a Web service specification in order to standardize the way sensors and sensor data are discovered and accessed on the Sensor Web. Multiple instances of this service can be implemented around the world, providing huge amount of data every moment. Each of these services operates in specific domain of knowledge (thematic), spatial and temporal dimensions. One way to reveal the underlying data over all of them is to provide an architecture for data integration to allow the user to query sensor data without the knowledge of the infrastructure components. In this research, a novel...
Crack Detection on Rotary Elements Using Vibration Analysis
, M.Sc. Thesis Sharif University of Technology ; Sayyaddi, Hassan (Supervisor)
Abstract
Rotating machinery are found in most industrial units, that are highly susceptible to transverse cross sectional cracks due to fatigue. The vibration pattern of a rotor system reflects the mechanical parameter changes in the system. These vibrations can be used for identifying the cracks and appropriate actions can be taken to prevent more damage to the system. The dynamic behavior of cracked rotor is a subject of considerable current interest. Several researchers have developed models of cracked rotor systems. Therefore, In this thesis, the influence of the presence of transverse cracks in a simple Jeffcott rotor is analyzed. In first, on the basis of fracture mechanics, the direct and...
Positioning, Tracking and Shape Control in Micro-Beams Via Electrostatic Actuators and Incomplete State Feedback
, M.Sc. Thesis Sharif University of Technology ; Salarieh, Hassan (Supervisor)
Abstract
Systems that are electrostatically actuated have found a vast role in MEMS application. This technology is used in optical systems, sensors, micro switches, and deformable mirrors. Raising the use of these systems in fields that needs better performance highlighted the need to accurate study of dynamics and control of electrostatic actuated systems in micro scale. This work is dedicated to design of an estimation and control system for a micro-beam that is actuated by electrostatic. After a comprehensive survey on pervious works that are done on dynamic, applications, fabrication and control of these systems dynamic of the system is fully derived. The environmental factors like fringing...