Effect of Remelting Processes on Microstructure and Segregation in Inconel-100 Superalloys Produced by VIM

, M.Sc. Thesis Sharif University of Technology Ahmadabadi, Morteza (Author) ; Tavakkoli, Ruhollah (Supervisor)

Abstract

In the present work, the effect of different methods of melting, remelting and solidification conditions on the microstructural evolution of IN100 superalloy was investigated. For this purpose, the superalloy was solidified within steel and ceramic molds to provide different cooling rates. Furthermore, the re-melting processes using ESR in the water circulated copper mold and ceramic molds, VAR and combined ESR and VAR were considered. The microstructure of alloy under different casting and remelting conditions were studied by means of optical and SEM microscopy and ESD analysis. According to our results, the ingot which was cast in the ceramic molds, due to lower cooling rate during...

Nonlinear Vibrations of Conical Shells with Concurrent Internal and External Flows

, Ph.D. Dissertation Sharif University of Technology Rahmanian, Mohammad (Author) ; Dehghani Firouz Abadi, Ruhollah (Supervisor)

Abstract

In the current study, nonlinear vibration and stability of conical shells with both separate and concurrent internal and external flows are studied. External and internal flows are in the supersonic and subsonic regimes, respectively. The Krumhar’s aerodynamic piston theory is utilized to model the external loading on the structure as well as the compressible potential flow model to capture the internal fluid dynamics. The so-called compressible fluid model is obtained via simplification of the Navier-Stockes equations after applying the inviscid and irrotational assumptions. The nonlinear structural equations of motion are derived using the Hamiltonian dynamics approach and utilizing the...

Vibration Modeling and Stability of Two Rigid Rotors Under the Influence of Internal Friction Caused by Slip on the Contact Surface of the Shrink-fit Connection

, M.Sc. Thesis Sharif University of Technology Amirabadizadeh, Hadi (Author) ; Dehghani Firouzabadi, Ruhollah (Supervisor)

Abstract

In this study, the modeling of shrink-fit connection was performed by considering the effect of friction on the connection. The behavior of a beam with shrink-fit connection was compared with the results of Adams software and the modeling accuracy was shown. Using both energy and Newton methods, the equations of motion of a rigid rotor consisting of two shafts connected by shrink-fit connection were obtained and the dynamic behavior of the rotor was investigated. Finally, the coupling parameters affecting the vibrations and stability of this rotor were introduced and the effect of each on the system behavior was shown.

Calculating the Stiffness Matrix of VACNTs Using Structural or Continuum Modelling

, M.Sc. Thesis Sharif University of Technology Vahidmoshtagh, Alireza (Author) ; Dehghani Firouz Abadi, Ruhollah (Supervisor)

Abstract

The goal of this research is investigation and analysis of a surface consists of vertically aligned carbon nanotubes (VACNTs) using continuum mechanics modeling. Today these kinds of surfaces also known as the darkest material have a particular importance in industries. Knowing the properties of a material is one of the most important things in analysis and designing using that kind of material, so extraxting the stiffness matrix of a material could be a big step for starting analyzing it. In this thesis a lattice of VACNTs with two different layouts and several unique geometrics is simulated using molecular dynamics approach using the Lammps software. The general stiffness matrix of the...

Thermal Simulation of Selective Laser Melting Process to Predict Microstructure

, M.Sc. Thesis Sharif University of Technology Dastbaz, Ehsan (Author) ; Tavakoli, Ruhollah (Supervisor) ; Ashuri, Hossein (Supervisor)

Abstract

In the process of Additive manufacturing for metals, the ability to predict and control the microstructure can reduce the need for subsequent heat treatment and accelerate the component quality assessment process. The ability to predict and control the microstructure of materials in the laser deposition method needs to understand the thermal conditions during the solidification process. For this purpose, the present study investigated the relationship between cooling rate and temperature gradient during local solidification, and control parameters of the laser deposition process such as power, beam radius, scanning speed and strategy of laser, ambient temperature and preheating temperature....

Reviewing and Analyzing the Political Marketing Program of Candidates for Parliamentary Elections on Social Networks (Twitter and Instagram) in Parliamentary Elections

, M.Sc. Thesis Sharif University of Technology Khiabani, Milad (Author) ; Karami, Naser (Supervisor) ; Honarvar, Ruhollah (Supervisor)

Abstract

With the emergence and expansion of social media in the societies, these media has become an integral part of modern society and the lives of citizens. These networks have improved communication facilities in the community and created an opportunity for politicians to use these media as a communication and marketing channel to communicate with citizens and use them to achieve their goals. Social media's ability to communicate has put politicians' relationship with citizens in a very strategic position. This has made it important to have a communication plan and, more generally, principled political marketing.Therefore, the main issue that this dissertation has investigated is the review of...

Analytical Modelling and Optimization of Disk Type, Slot Less Resolver

, M.Sc. Thesis Sharif University of Technology Moheyseni, Atefeh (Author) ; Nasiri Gheidari, Zahra (Supervisor)

Abstract

Resolvers, due to their robust structure, are widely used in automation systems. Among the types of resolvers, the accuracy of the Wound Rotor (WR) resolver in the occurrence of common mechanical errors is higher than other types of resolvers. therefore, in this thesis, an AFWRR is studied to improve the performance. Increasing the number of poles in WR resolvers is a good solution for increasing the accuracy of these electromagnetic position sensors. However, high-speed WR resolvers due to employing fractional slot windings suffer from rich sub-harmonics in the induced voltages. A common solution for suppressing the undesirable sub-harmonics is using multi-layer winding with appropriate...

Fabrication, Characterization and Field Emission Study of GLAD Tungsten Nanostructures

, M.Sc. Thesis Sharif University of Technology Shaker, Tayebeh (Author) ; Moshfegh, Alireza (Supervisor) ; Azimirad, Ruhollah (Supervisor)

Abstract

Recently nanostructure materials have used in various technologies and hence an extensive part of research focused on preparing and optimization of growth of nanostructure materials. Usually common procedure is based on a two-step process. First, construction a pre-layer by means of different deposition methods and then formation a nanostructure with a thermal treatment which increases the cost of research. Hence with one step method such as glancing angle deposition (GLAD ( it is possible to form a desirable structure with low cost. In this research Nano columns of tungsten was deposited on Si(133) by means of GLAD-RF sputtering without any heat treatment at substrate rotational speed ( )...

Evaluating the Effect of Antiviral Agents on Influenza H1N1 Virus

, M.Sc. Thesis Sharif University of Technology Haghayegh Khorasani, Sara (Author) ; Roosta Azad, Reza (Supervisor) ; Dorostkar, Ruhollah (Supervisor)

Abstract

With the epidemic of viral diseases in humans and animals, and their potential to cause irreparable economic damages, due to their recent noticeable changes in their structures followed by becoming antibiotic resistance, many researchers nowadays are focusing on the new antiviral Agents with least side effects. Influenza A virus is a common seasonal virus which can lead to sever infections. This type of influenza has the ability to transmit between humans and animals, and also by antigenic shifts can transform to new type of influenza which can cause a global disaster. While classical antiviral drugs are still in use for influenza patients, new influenza A subtypes become resistant to these...

Massive Online Open Courses and Higher Education Policy in Iran

, M.Sc. Thesis Sharif University of Technology Amini Abarghouie, Mohammd Ali (Author) ; Miremadi, Iman (Supervisor) ; Honarvar, Ruhollah (Co-Supervisor)

Abstract

The digital age and its interlace with the pandemic has led to rapid changes in various institutions, including higher education. One of the factors that changes higher education is the expansion of E-learning and Massive Online Open Courses (MOOCs). Although about 15 years have passed since its creation, the pandemic has expanded the E-learning infrastructure and given it more attention, so that now everyone Confesses the possibility of distance education. On the other hand, although the development of MOOCs platforms and their considerable acceptance has attracted the attention of higher education professors and future researchers in this field, it is not properly considered by the...

Choosing the Optimal Assembly Angle of Multi-Part Elastic Rotor Components with the Aim of Passing Critical Speeds

, M.Sc. Thesis Sharif University of Technology Ghamari, Mohammad Amin (Author) ; Dehghani Firouzabadi, Ruhollah (Supervisor) ; Amirzadegan, Sadegh (Co-Supervisor)

Abstract

Multi-part rotating parts are used in various industries with very high revolutions. Therefore, the method of assembling each part and keeping the axis of rotation of each part close to the axis passing through two supports (bearings) is important. In this research, three main steps are followed, the development of the differential equations governing the multi-part rotating system and the calculation of the range of oscillations created at the critical points, and then the calculation of the optimal assembly angles with the aim of reducing the introduced oscillations, and finally the discussion of crossing the speeds A crisis is being investigated. The method of obtaining the system of...

Design, analysis, and prototyping of a new wound-rotor axial flux brushless resolver

, Article IEEE Transactions on Energy Conversion ; Volume PP, Issue 99 , 2016 ; 08858969 (ISSN) Nasiri Gheidari, Z ; Sharif University of Technology

Institute of Electrical and Electronics Engineers Inc 2016

Abstract

Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this study, a new axial flux brushless resolver (AFBR) with a wound rotor is introduced. In the proposed resolver, the core of the rotary transformer (RT) is omitted, and an innovative design is used to supply the excitation winding of the resolver. The proposed resolver can be built with smaller dimensions, and its thermal stability and mechanical strength are increased compared with conventional AFBRs. The performance of the proposed structure is simulated and optimized by using a 3-D time-stepping finite element method. The effect of the leakage flux of the rotary transformer on the...

Design, performance analysis, and prototyping of linear resolvers

, Article IEEE Transactions on Energy Conversion ; Volume 32, Issue 4 , 2017 , Pages 1376-1385 ; 08858969 (ISSN) Nasiri Gheidari, Z ; Sharif University of Technology

2017

Abstract

Linear position sensors are widely used in linear motion-control systems. In this paper, the design, optimization, performance analysis, and prototyping of a linear resolver (LR) are discussed. Mathematical model of the proposed structure is presented based on a simple design-oriented method. Then, a comprehensive iterative design algorithm considering design constraints of linear electromagnetic sensors is proposed. All resistances and inductances of the designed LR are calculated based on the design parameters. Then, a 3-D time-stepping finite-element method is used to validate the design, optimization, and analytical model. Finally, a prototype of the sensor is built and tested....

Design, Analysis, and prototyping of a new wound-rotor axial flux brushless resolver

, Article IEEE Transactions on Energy Conversion ; Volume 32, Issue 1 , 2017 , Pages 276-283 ; 08858969 (ISSN) Nasiri Gheidari, Z ; Sharif University of Technology

Institute of Electrical and Electronics Engineers Inc 2017

Abstract

Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this study, a new axial flux brushless resolver (AFBR) with a wound rotor is introduced. In the proposed resolver, the core of the rotary transformer (RT) is omitted, and an innovative design is used to supply the excitation winding of the resolver. The proposed resolver can be built with smaller dimensions, and its thermal stability and mechanical strength are increased compared with conventional AFBRs. The performance of the proposed structure is simulated and optimized by using a three-dimensional time-stepping finite element method. The effect of the leakage flux of the RT on the excitation...

Fabrication of porous scaffolds with decellularized cartilage matrix for tissue engineering application

, Article Biologicals ; Volume 48 , 2017 , Pages 39-46 ; 10451056 (ISSN) Nasiri, B ; Mashayekhan, S ; Sharif University of Technology

Academic Press 2017

Abstract

Due to the avascular nature of articular cartilage, damaged tissue has little capacity for spontaneous healing. Three-dimensional scaffolds have potential for use in tissue engineering approach for cartilage repair. In this study, bovine cartilage tissue was decellularized and chemically crosslinked hybrid chitosan/extracellular matrix (ECM) scaffolds were fabricated with different ECM weight ratios by simple freeze drying method. Various properties of chitosan/ECM scaffolds such as microstructure, mechanical strength, swelling ratio, and biodegradability rate were investigated to confirm improved structural and biological characteristics of chitosan scaffolds in the presence of ECM. The...

Dynamic FPGA-accelerator sharing among concurrently running virtual machines

, Article Proceedings of 2016 IEEE East-West Design and Test Symposium, EWDTS 2016, 14 October 2016 through 17 October 2016 ; 2017 ; 9781509006939 (ISBN) Nasiri, H ; Goudarzi, M ; Sharif University of Technology

2017

Abstract

Using an FPGA as a hardware accelerator has been prevalent, to speed up compute intensive workloads. However, employing an accelerator in virtualized environment enhances complexity, because accessing the accelerator from virtual machines has significant overhead and sharing it needs some considerations. We have implemented adequate infrastructure to share an FPGA-based accelerator between multiple virtual machines with negligible access overhead which dynamically implements virtual machines' accelerators. In our architecture each user process from a virtual machine can directly access the FPGA over PCIe link and reconfigure its accelerator in the specified part of FPGA at run-time. The...

Simulation and visualization environment for nonlinear helicopter flight dynamics

, Article General Aviation Technology Conference and Exhibition, Wichita, KS, 29 August 2006 through 31 August 2006 ; 2006 ; 01487191 (ISSN) Nasiri, M ; Rezazade, M ; Sharif University of Technology

SAE International 2006

Abstract

The Analytic 6 D.O.F. dynamic model of a helicopter is developed for 3D computer generated imagery simulator. Analytic expressions for the forces and moments on the various helicopter components are derived. By using the forces and moments equilibrium, helicopter trim point is determined using Newton's method of solving the nonlinear set of trim equations. The equations of motion for the fuselage six degree of freedom are assembled by applying Newton's law of motion relating the applied forces and moments to the resulting translational and rotational acceleration. Visual C++ programming software, utilized as a platform will interact to MATLAB Aircraft Instrument ActiveX and 3DSTATE for...

Path-planning and Control of Space Robots

, M.Sc. Thesis Sharif University of Technology Nasiri, Mahdi (Author) ; Namvar, Mehrzad (Supervisor)

Abstract

Control of many mechanical systems such as satellites lies on the control of space robots. Control of space robots has many theoric complexities because of the presence of non-holonomic constraints due to angular momentum conservation. Unlike fixed-base robots, any movement of space robots manipulator has a reaction on the robot base and moves it. Thus manipulator’s movement toward desired configuration rotates the robot base and as a result appropriate attitude may not be attained. Therefore an appropriate path is required to achieve the desired configuration and the base attitude reaches its desired value. In this thesis, first the dynamic of space robots and the interaction between the...

"The Paakshooy": A Robotics Cell for Washing and Preparation of a Cropse for Burial Compatible with Islamic Laws

, M.Sc. Thesis Sharif University of Technology Nasiri, Ehsan (Author) ; Meghdari, Ali (Supervisor)

Abstract

Washing a dead person’s body and dressing the corpse prior to burial is an act of love and necessity in many religions. Since the deceased loses all bodily functions at time of death, cleaning the body to eliminate odors is generally a hard and unpleasant task for many to perform. It has also been reported that tens of thousands of microbes are present on every square centimeter of a human corpse which is always a health risk to the persons performing the task. Among Islamic nations, preparation of the corpse is usually carried out in washing rooms (Ghassalkhaneh) of cemeteries in large cities. This preparation consists of two important operations namely as washing of the corpse (Ghosl)...

Inventory Ordering System with Fuzzy Parameters in Supply Chain

, M.Sc. Thesis Sharif University of Technology Nasiri, Mohsen (Author) ; Hajji, Rasool (Supervisor)

Abstract

Inventory control has been always considered important due to its prominent role in managing and better application of resources in the field of operational systems. Ordering system or review stock policy in supply chain management can be mentioned as one of the inventory control study fields of management. A lot of researches have been done in investigating ordering system in supply chain under certainty conditions; however, since the real world is full of uncertainties, parameters such as demand cannot be predicted exactly and we encounter with ambiguity. In this case, using crisp (exact) values can cause to decide wrongly (a wrong decision). On the other hand, due to absence of sufficient...