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Investor Experience in Chabahar Free Zone: Scale Generation
, M.Sc. Thesis Sharif University of Technology ; Najmi, Manoochehr (Supervisor) ; Arian, Hamidreza (Supervisor)
Abstract
Free economic zones in Iran have been established with the goal of developing infrastructure, improving living conditions, fostering economic growth, attracting capital and increasing income, productive job creation, regulating job and goods market, maintaining active presence in international and regional markets, manufacturing and exporting of goods and providing public services. Yet many free economic zones have fallen short of these goals. Considering the government's inability to fund the development of the free economic zones with its limited financial capacity and shortcomings in terms of management system, it is imperative to the development of these regions that private sector...
Robust facility layout design for flexible manufacturing: a doe-based heuristic
, Article International Journal of Production Research ; 2021 ; 00207543 (ISSN) ; Salimpour, S ; Akhavan Niaki, S. T ; Azab, A ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
Flexible manufacturing systems (FMS) should be able to respond to changing manufacturing requirements and environments. From the layout point of view, FMS need to be rearranged to fit the new requirements. However, rearranging the layout is often undesirable due to its unpredicted high costs and production disruption. This paper proposes a practical approach to mitigate the effects and repercussions of changing environments and avoid rearranging the layout. A robust layout approach is presented, where changes in product demand and mix are absorbed by altering product routes and not rearranging the layout. In this approach, the problem is decomposed into two sub-problems: sub-problem 1 (SP1)...
Robust facility layout design for flexible manufacturing: a doe-based heuristic
, Article International Journal of Production Research ; Volume 60, Issue 18 , 2022 , Pages 5633-5654 ; 00207543 (ISSN) ; Salimpour, S ; Akhavan Niaki, S. T ; Azab, A ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
Flexible manufacturing systems (FMS) should be able to respond to changing manufacturing requirements and environments. From the layout point of view, FMS need to be rearranged to fit the new requirements. However, rearranging the layout is often undesirable due to its unpredicted high costs and production disruption. This paper proposes a practical approach to mitigate the effects and repercussions of changing environments and avoid rearranging the layout. A robust layout approach is presented, where changes in product demand and mix are absorbed by altering product routes and not rearranging the layout. In this approach, the problem is decomposed into two sub-problems: sub-problem 1 (SP1)...
Numerical Simulation of Residual Stress Formation During Selective Laser Melting Process
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
One of the major challenges in Additive Manufacturing is the creation of residual stresses due to the high temperature gradient in the solidification zone. This will cause problems such as cracks in the structure, metallurgical defects as well as deformation and dimensional accuracy reduction in the finished product. The purpose of this study is to perform mathematical modeling and computer simulation of the selective laser melting process (SLM) to predict these stresses as well as identify the effective parameters on this phenomenon. The conditions were adjusted in this model with the actual coefficients of the device. Additionally, the powder used in this project is Ti6Al4V material. By...
Bi-objective optimization of a three-echelon multi-server supply-chain problem in congested systems: Modeling and solution
, Article Computers and Industrial Engineering ; Volume 99 , 2016 , Pages 41-62 ; 03608352 (ISSN) ; Rashidi Kahag, M ; Akhavan Niakib. S. T ; Pourvaziri, H ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
A novel bi-objective three-echelon supply chain problem is formulated in this paper in which cross-dock facilities to transport the products are modeled as an M/M/m queuing system. The proposed model is validated using the epsilon constraint method when applied to solve some small-size problems. Since the problem belongs to the class of NP-hard and that it is of a bi-objective type, a multi-objective particle swarm optimization (MOPSO) algorithm with a new solution structure that satisfies all of the constraints is developed to find Pareto solutions. As there is no benchmark available in literature, three other multi-objective meta-heuristic algorithms called non-dominated ranking genetic...
Synthesis and swelling behavior of a new superabsorbent hydrogel network based on polyacrylamide grafted onto salep [electronic resource]
, Article Journal of Applied Polymer Science ; Volume 112, Issue 5, pages 2625–2633, 5 June 2009 ; Rezanejad Barajee, Ghasem ; Soleyman, Rouhollah ; Sharif University of Technology
Abstract
Synthesis and swelling behavior of a new superabsorbent hydrogel based on natural salep grafted with polyacrylamide is described. The new superabsorbent hydrogel biopolymer was synthesized via radical crosslinking and graft copolymerization of acrylamide monomer onto salep backbones. Regarding to the water absorption of hydrogel, the best synthesis condition is reported. FTIR spectroscopy and thermogravimetric analysis were used to confirm the structure of the final product and a mechanism for superabsorbent hydrogel formation was also suggested. After preparing the desired hydrogels based on optimum condition, several factors affecting the swelling behavior of hydrogel including pH of...
Phase Field Simulation of Microstructure Ternary Eutectic Solidification
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
Physical and mechanical properties of cast alloys is partly a function of the morphology and volume fraction of phases from freezing. The microstructure of the eutectic solidification is function of physical properties (especially mobility and surface tension) and the volume fraction of phases involved in the evolution. The prediction of solidification microstructures will be very helpful for improving the mechanical properties of casting alloys and designing of new families of alloys. The theoretical study of the formation of eutectic microstructures is very difficult and almost impossible in general cases and empirical studies are expensive. The purpose of this study is to predict the...
Optimal Design of Parting Line in the Shape Casting Processes
, M.Sc. Thesis Sharif University of Technology ; Tavakkoli, Rouhollah (Supervisor)
Abstract
More than 70 weight percentage of using parts in diverse industries (such as military, civil, automobile productions and etc.) are produceed by the casting processes. For each one of the casting procceses, mold cavity is requisite for arrived molten metal in the mold cavity to get eventuated as a solidified part. Based on mold ilk, if the mold is permanent, the cast part must be capable to be remoeved from the the mold inside. For the non-permanent mold (asssuming multi-piece and non-monolithic), if the model requires to be removed from the mold inside after molding and before casting, only model (no cast part) has to be moldable (why for removing the solidified cast part from the...
Production of Sn Base Composite Solder Reinforced by Nanoparticles Via Melt-spinning Technique
, M.Sc. Thesis Sharif University of Technology ; Tavakkoli, Rouhollah (Supervisor)
Abstract
Lead-containing solder alloys in particular Sn-37Pb is the most common alloy used in electronics industry, this alloy has the good mechanical properties and excellent wetting properties and low prices. Recently, increasing environmental and health concerns over the toxicity of lead combined with strict legislation to ban the use of lead-based solders have provided an inevitable driving force for the development of lead-free solder alloys. A group of these lead-free solders are nanocomposite solders that because of having the reinforcement nano particles exhibit lots of unique properties, such as good mechanical and thermal properties. The aim of this research produce a new tin base...
A Phase-Field Model for Inhomogeneous Multiferroic Materials
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
In this thesis, by deliberately embedding “emplacements” in the system to locally break the inversion and the time reversal symmetries, the manifold of all possible microstructures is navigated in pursuit of the one that can give rise to maximal magnetoelectric effect mediated by elastic energy of piezoelectric-piezomagnetic phases via their interface --- needless to mention the low intensity of such an effect in single-phase multiferroics. The configuration with the maximal coupling is sought within the context of phase-field modeling. In order to numerically track the conserved dissipative dynamics of the interface (namely, the Cahn-Hilliard equation) --- that is nonlocal by the nature of...
Simulation of the Effect of Cooling Rate and Chemical Composition on the Atomic Structure of Bulk Metallic Glass Iron-Phosphorus and Nickel-Phosphorus
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
bulk metallic glass Unlike metal materials that have a crystalline structure, amorphous glass is an amorphous material with an irregular atomic structure that simultaneously has the same physical properties as metals. Due to the absence of crystal defects such as dislocation and grain boundaries, these materials show unique mechanical properties such as high strength and elastic strain, abrasion resistance and proper corrosion. However, their plastic deformation is heterogeneous, concentrated, and accompanied by sudden failure. Unlike metals, these materials do not have a long-range crystalline order, and their atomic structure includes short-range and mid-range order. The short-range order...
Vibration and Buckling Analysis of Thick FGM Conical Shells Under Variable Thermal and Pressure Distributions, Considering Initial Geometric Imperfections Using a Higher Order TheoryVibration and Buckling Analysis of Thick FGM Conical Shells Under Variable Thermal and Pressure Distributions, Considering Initial Geometric Imperfections Using a Higher Order Theory
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
The current study is dedicated to free vibration and buckling analysis of thick FGM conical shells conveying hot flows with the consideration of initial geometric imperfections. To this end, the higher order governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. Due to the solution procedure of Frobenius series expansion, the differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Radial and longitudinal temperature distributions are considered while pressure distribution and geometric imperfection variations are found to be in longitudinal direction, only. The final...
On the Stability of Rotating Cylinder Conveying Flow in an External Fluid Medium
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
The present study aims at investigating the stability of flexible spinning cylinders conveying flow in an external fluid Medium. Using the linearized Navier-Stokes equations for the flow, a two-dimensional model is developed governing the fluid motion. The resultant force exerted on the flexible cylinder wall due to the fluid interactions is calculated as a function of the lateral acceleration. Applying the Hamilton principle, the governing equations of flexural vibration of the rotary flexible cylinder mounted on simply supported axles are derived. Having the forces due to the conveying fluid calculated and substituting into the governing equations, a coupled field governing equations of...
Thermal Optimization of Plain-Carbon Steel Continuous Casting Process
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
Continuous casting is one of the ingot production methods in which the product has uniform chemical structure, low defects and high production rates. These days, carbon steel and nonferrous alloys are mainly produced by this special method. The design of continuous casting process includes a lot of difficulties due to its technological complexity. One of the most important aspects of this process is the heat transfer during solidification. In the present study, a new mathematical model and its corresponding numerical solution method have been introduced to establish the condition of directional solidification along the major ingot’s axis. The controlling parameters used in the model are...
Investigation of Vibration and Stability of Graphene NanoRibbone under Magnetic field Effect
, Ph.D. Dissertation Sharif University of Technology ; Dehghani Firouzabadi, Rouhollah (Supervisor)
Abstract
This study aims at investigating the vibration analysis and stability of Graphene Nano-Ribbon (GNR) under a magnetic field using continuum mechanics approach and an efficient hybrid modal-molecular dynamics method. The force distribution on the GNR due to the magnetic field is determined by Maxwell's equations, Biot-savart law, magnetic dipoles and Lorentz force law.
Using the continuum mechanics model, the vibration of the GNR in a magnetic field is investigated by some problems and the resonance frequencies, stability boundaries and critical load are studied.
Furthermore, in this present study, an efficient hybrid modal-molecular dynamics method is developed for the vibration...
Using the continuum mechanics model, the vibration of the GNR in a magnetic field is investigated by some problems and the resonance frequencies, stability boundaries and critical load are studied.
Furthermore, in this present study, an efficient hybrid modal-molecular dynamics method is developed for the vibration...
Free Vibration and Aeroelastic Stability Analysis of Truncated Conical Panels in Supersonic Flows
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
The current study is dedicated to free vibration and Aeroelastic Stability Analysis of Truncated Conical Panels in Supersonic Flows. Governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. The aeroelastic stability problem is formulated based on first-order shear deformation theory as well as classical shell theory with the linearized first-order piston theory for aerodynamic loading and solved using Galerkin method. The flutter boundaries are obtained for truncated conical shells with different semi-vertex cone angles, different subtended angles, and different thickness
Developing the Nonlinear Model of Single-Cell Thin-Walled Closed-Section Composite Beams
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
The purpose of this study is to develop the reduced order nonlinear modeling of single cell closed section thin walled composite beams. In this way, global behavior of one dimensional beam under axial load, bending and torsional moment is produced. This model is based on the classical lamination theory, and the nonlinear model is developedby usingthe von-karman strains. In this process the effects of material anisotropy and axial warping are considered. Numerical results are obtained for thin-walledcomposites box beams, addressing the effects of fiber angle and laminate stacking sequence. The nonlinear model is compared with theoretical results of homogeneous beams and the natural...
Molecular Dynamics Study of Tungsten and Iron Addition on the Glass Formability of Cobalt-based Electrodeposited Coatings
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
Recent research suggests that the electrochemical deposition of cobalt-based binary alloys, such as cobalt-tungsten and cobalt-iron, can lead to the formation of amorphous structures in the coatings. Theoretical studies suggest that these structures are equivalent to structures created by the melt cooling of the alloy at speeds of about 〖10〗^10 Kelvin per second. The formation of a glass phase can significantly increase the abrasion resistance and corrosion resistance of these coatings. Empirical studies show that the ability of the glass to become glassy, or more precisely, the transition from crystalline to amorphous, is largely a function of the chemical composition. Simulation of...
Aero-Hydro-Elastic Analysis of a Floating Beam in a Water Channel Subjected to Cross Wind
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Rouhollah (Supervisor)
Abstract
In static floating structures such as floating bridges and offshore runways that are in contact with the water surface from the floor and with the open air from the top, three types of interactions occur: the interaction of the structure with air, the interaction of the structure with water and Interaction of air with water. Due to the long length of such structures and approaching their natural frequencies to the standing wave frequencies (seiche frequencies), the analysis of the elastic behavior of the structure alone is not enough, but the structure-air-water interaction must be evaluated simultaneously in a system. Leading research addresses this issue and examines the behavior of an...
A Phase Field Model for Simulating the Pitting Corrosion
, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rouhollah (Supervisor)
Abstract
Corrosion is an electrochemical process that results in the degradation of metallic materials in a corrosive environment. Localized corrosion is a destructive form of corrosion that can lead to catastrophic failure of structures. In developed countries, corrosion costs more than 3% of gross national product every year, much more than the costs arisen from all-natural disasters combined. It is very important to understand this process to prevent sudden accidents and also develop high strength corrosion resistant metallic materials. This study presents the formulation and implementation of a phase field model for simulating the activation- and diffusion-controlled pitting corrosion phenomena...