Sharif Digital Repository

Well worn gas turbine blade made of Nickel based superalloy, IN738LC was remelted due to remove inclusion and use it in casting process of new blade after microstrucrure investigation in neutral atmosphere and vacuum. The composition of slags for removing inclusions used for this practice were 70CaF2-20CaO-10Al2O3 and 55CaO-45Al2O3. The microstructural characterization involved use both optical as well as electron microscope including application of EDS technique for denoted the type of carbides and inclusion investigation. Chemical composition was determined by despersive spectroscopy method. The changing in main elements were reported too low. Number of inclusions were decreased in the... 

Because of the importance and value of Superalloy, In this research has been treid to remelting scrap of gas turbine blades cobalt based Superalloy X-45, In order to restore it to the cycle of consumption. For this purpose, scraps were remelted under different conditions, for example changing the atmosphere, changing slag composition, changing type of the furnace for remelting and changing time of remelting process. Then in order to investigate effect of the above factors, microstructure were studied by optical microscope and Scanning Electron Microscopy (SEM) And also in order to investigate changings of element composition, chemical analysis were examined by atomic absorption analysis and... 

The results of numerical simulation of underground flows are greatly affected not only by the discretization method of flow equations, but also by the way that the geological domain is upscaled. Including the detailed knowledge of heterogeneous permeability distribution is mostly neither feasible nor computationally efficient. So it is important to develop efficient grid generation and upscaling methods to simplify the fine-scale flow model while still including the impact of the heterogeneities as far as possible. Thus regions where parameters of interest have larger values or higher changes require finer grid blocks and regions with lower values or minor changes should have coarser grid... 

The purpose of this investigation was to study the microstructure of the Inconel718 alloy wich was produced by VAR and suction casting method, and study the effect of cooling rate on the solidification structure of Inconel718 alloy. In the first a labratoary scale VAR furnace was made. After producing some sample's with this furnace, a suction casting sample was produced using a 3mm diameter copper mold. Metallography, SEM, EDS, and microhardness analysis was carried away. Cooling rate evaluation was done by using a equation between secondary dendrite arm spacing and solidification time. Results showed that by increasing cooling rate from 63 c/s to around 2000 c/s, columnar and equiaxed... 

Nowadays spam has become as a universal problem which all email users are familiar with it. Studies show that a large proportion of sent emails are spam. Obviously it results in wasting a vast range of resources. There is different ways to fight spam; each of them has its own strengths and weaknesses. The most common filtering technique is content based filtering. This problem has been addressed as a text classification problem. Two main defect of spam filtering techniques are manually definition of rules and circumventing them, one solution for overcoming this problem is applying machine learning algorithms. Spam classification using machine learning techniques is very successful and... 

In this study, the influence of eutectic modification, grain refining and cooling rate on amount of shrinkage porosity in aluminium A356 alloy were investigated. Modification process for changing the morphology of eutectic silicon from needle like to fibrous like, use in aluminium – silicon alloys. This process often leads to increasing porosity in melt and affect harmfully on mechanical properties. For studying shrinkage porosity, the melt degassed completely to minimizing amount of gas in the melt. For modification, strontium in Al-10Sr master alloy and sodium in NaF salt used and for grain refining Al-10Ti and Al-5Ti-1B master alloys used. To study the effect of cooling rate, three mold... 

The oil refining industry, as the first oil supply chain, is of great importance. By examining the issue of the Iranian Oil Refining Industry, using the game theory, one can find an accurate analysis of the barriers to the development of this industry. For this purpose, the main factors affecting the oil refining industry, the government and the refinery's owner, are modeled and their benefits are considered. By examining the relationship between these actors and their actions, the following strategies are proposed to improve the administration and regulate the Iranian oil refining industry:
1- Refining feed prices, according to the quality of crude oil (sulfur content and API... 

Automatic translation of a high-level specification language to an executable implementation would be highly useful in maximizing the benefits of formal methods. We will introduce a set of translation functions to fill the specification-implementation gap in the domain of database applications. We chose Z, SQL and Delphi languages to illustrate our methodology. We extend Delphi libraries to support mathematical objects exist in Z. Then, based on the extended libraries, we extract the translation functions from Z to Delphi. The translation functions from Z to SQL are more easily extracted, because the mathematical foundation of Z has many properties in common with SQL. Based on the extracted... 

Samples of INCONEL 718 were levitated and melted in a slag by the application of an electromagnetic field. The effects of temperature, time and slag composition on the inclusion content of the samples were studied thoroughly. Samples were compared with the original alloy to study the effect of the process on inclusions. Size, shape and chemical composition of remaining nonmetallic inclusions were investigated. The samples were prepared by Standard Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel (ASTM E 768-99) method and the results were reported by means of the Standard Test Methods for Determining the Inclusion Content of Steel (ASTM E 45-97).... 

Reservoir simulation models are profound tools in reservoir management. Number of grid blocks in a simulation model is much less than the number of grid blocks in geological model, therefore geological model must become upscaled in order to construct simulation model with convenient dimensions. This causes loosing of some details and introduces errors due to discretization and homogenization. One method of construction of an efficient computational grid is use of adaptive mesh refinement (AMR) methods. These methods refine computational grid in regions needing further resolution. An error indicator is used for determining regions candidate for refinement or coarsening. In present study... 

Inrecent years,research onionic liquidsarehighly developed. Because ofthe uniqueproperties ofionic liquidssuch asnegligiblevapor pressureandthermalstability for use inlarge areasofmajor industries have been considered.However,ionic liquids because they have lessenvironmental wasteas an alternative to convention alorganic solventssuch asaminesalkanolanarise.Ionic liquid sassolventsfor theremoval ofacid gases such as water and gasare investigated. The solubility of CO2 and H2S in the [Emim] [OTF] (1-ethyl-3-methylimidazolium triflate) in the temperature range 303.15 to 343.15 K and pressures up to 2 MPa has been studied experimentally. In order to capture modeling, the model equations of state... 

In recent years, most of the programmer’s problems are solved using Q&A websites, e.g. Stack Overflow. Since the number of users, questions and answers in these websites are rapidly increasing, manually moderating and enhancing the quality of the posts (specially the answers) seems to be impossible. Despite the various studies on issues with Q&A websites and facilitating their use, there has been no studies on the field of improving the quality of answers. In this study, we intend to provide an appropriate solution to enhance the problem of low-quality answers. In order to demonstrate the proposed approach, we recommend a tool called StImp, which is a plugin for Eclipse. Using this plugin,... 

Object oriented analysis and design hase become the paradigm of choice for many software builders. For, it has filled the gap between the problem domain and its solution. However, most of object oriented methods can not prove their model against the software specification and do not ensure that they realize what the customer needs. Formal method is one of the methods used for building softwares. Since a software is specified accurately by this method, the specification can be used to build the software in addition to being used as a test for the final software. A specification can be refined to code step by step. Since an object oriented model is close to problem domain in real world, a... 

A356 Aluminium alloy has an abundant application in the aerospace and automobile industries. One of the most important problems of the alloy is in it’s microstructure after solidification with long dendrite grain of Aluminium.It is stated that solidied grains can be refined by electromagnetic vibration and an alternative electric feild applied simultaneously. To make electric field, electric current passed through the specimen. In order to change in microstructure, electromagnetic vibration was used. Then the effect of intensity of electromagnetic field and alternative electric current on microstructure was examined.Grain refining carried out at electric current 80A and magnetic flux of 13,... 

The presented work provides a calculus for refining an object oriented formal specification to an object oriented code. A refinement calculus provides a framework to produce executable code from a specification while preserving its correctness. Eiffel Refinement Calculus is the most complete work in this domain which is studied in this research.
The Formal specification language which is considered for this purpose is .JML to specify executable code in .Java language. For this calculus some refinement laws are pre- sented and their proofs is given by weakest precondition predicate transformer, a work which was not considered in Eiffel Refinement Calculus. The constructs which are used in... 

In this project, the melting, solidification and remelting processes and also, the epitaxial growth of thin molten layer on the solidified crystalline substrate is studied using molecular dynamics simulation for the aluminum as an instance for the fcc metals. Sutton-Chen potential is used for energy calculations; the modified version of verlet algorithm is used for determination of position and velocity of atoms; and the berendsen algorithms are used as thermostat and barostat. The effects of pressure and temperature changing rate on the melting and crystallization temperatures and the crystal structure are investigated. The crystal structure of the system is examined using radial... 

In this study, static recrystallization (Rex) of a low carbon steel after cold rolling has bees simulated under non-isothermal condition by employing cellular automata (CA) method. Symmetric cold rolling and asymmetric cold rolling (ASR) which was arisen by inequality of friction coefficient have been applied as primary cold deformation. Residual stress and strain field after deformation, and temperature rate and distribution of specimens during annealing has been evaluated by employing two different models based on finite element method. Initial microstructure has been developed by haphazardly distribution of grains and topological adjustments were imposed on it. Results of FEM models were... 

Under Linear Elastic Fracture Mechanics (LEFM) assumptions, the stress at the crack tip is theoretically infinite. Clearly all materials have a finite strength, thus there will always be a plastified zone around the crack tip. If the size of plastic zone is not small compared to the crack size, then linear elastic assumptions are not applicable and a nonlinear model must be used. This damaged zone is referred to as a plastic zone for metals, and a fracture process zone for cementitious materials and ceramics. In this regard a discrete extrinsic cohesive crack model with bilinear traction separation constitutive law, i.e. softening function, is employed and crack propagation is investigated.... 

The main goal of this thesis is to develop and implement a variable Impedance control method with the ability to refine the desired gait in an online manner. For this purpose, a dataset consisting of 89 healthy gaits was utilized. Then, “Basic shapes” were driven using principal component analysis and their meaningfulness was investigated. Regarding the meaningfulness of coefficients of basic shapes, a normality metric was defined to evaluate the human gaits. Furthermore, as a reference gait refinement in Impedance control, an outer loop was added to change the desired gait, according to traversed gait. Kalman filter was used to estimate the coefficients of basic shapes in this loop. In... 

In this research, the dynamic behavior of a rotating stiffened cylindrical shell has been investigated using the refined finite element method. Refined FEM means decreasing degrees of freedom based on decoupling the structure to longitudinal and layerwise directions. The refined FEM has been used to solve the 3D rotor dynamics equations. The natural frequencies and the corresponding modes have been calculated and verified for some existed data and problems. In addition, the effects of the shell geometry dimensions on the natural frequencies and mode shapes have been studied. Also, the relationship between the length to radius ratio, radius to thickness ratio, rotational speed, Aspect ratio...