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Effect of Mold Hardness on Microstructure and Contraction Porosity in Ductile Cast Iron
, Article Journal of Iron and Steel Research International ; Volume 18, Issue 4 , 2011 , Pages 44-47+67 ; 1006706X (ISSN) ; Amin Ahmadi, B ; Sharif University of Technology
2011
Abstract
The effect of mold hardness on the microstructure of ductile iron and the contraction porosity was investigated. Molds with different hardnesses (0.41, 0.48, 0.55, 0.62 MPa) and a sand mold prepared by Co2 method were used. The influence of silicon content on the induced expansion pressure owing to the formation of graphite was also investigated. The contraction during solidification can be compensated by an induced expansion owing to the graphite relief when the hardness of mold increases; therefore, the possibility of achieving a sound product without using any riser increases
The effect of chemical composition on enthalpy and entropy changes of martensitic transformations in binary NiTi shape memory alloys
, Article Journal of Alloys and Compounds ; Volume 487, Issue 1-2 , 2009 , Pages 363-366 ; 09258388 (ISSN) ; Amin Ahmadi, B ; Sharif University of Technology
2009
Abstract
In the present research work the binary NiTi alloys with various compositions in the range of 50.3-51 at.% Ni were used. Samples have been annealed at 850 °C for 15 min and then quenched in water. In order to characterize transformation temperatures and enthalpy changes of the forward and the reverse martensitic transformation, Differential Scanning Calorimetric (DSC) experiments were performed. The enthalpy and entropy changes as a function of Ni atomic content have been thermodynamically investigated. Results show that enthalpy and entropy changes of martensitic transformation decrease when Ni atomic content increases. The variation of enthalpy and entropy of martensitic transformation...
Biocompatibility and corrosion behavior of the shape memory NiTi alloy in the physiological environments simulated with body fluids for medical applications
, Article Materials Science and Engineering C ; Volume 30, Issue 8 , 2010 , Pages 1112-1117 ; 09284931 (ISSN) ; Amin Ahmadi, B ; Zare, M ; Sharif University of Technology
2010
Abstract
Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of...
Failure analysis of a gas turbine compressor in a thermal power plant
, Article Journal of Failure Analysis and Prevention ; Volume 13, Issue 3 , 2013 , Pages 313-319 ; 15477029 (ISSN) ; Farrahi, G. H ; Masoumi Khalil Abad, M ; Zare, A. A ; Parsa, S ; Sharif University of Technology
2013
Abstract
This study presents the results of failure analysis of a 28 MW gas turbine at the Rei electrical power plant. The gas turbine failed during the shutdown period and near its second natural frequency at 4200 rpm. Initial inspections revealed that the compressor disk of stage 15 was fractured, and all of the stationary and rotary blades of stages 14-18 of the compressor had been detached or broken from the dovetail region of the disks. The fracture roots were investigated by performing finite element modeling and fractography analysis. It was shown that a crack was initiated from the disk edge on its interface with the rotor shaft and was propagated under cyclic loading. As a result of the...
EEG based biometrics using emotional stimulation data
, Article 5th IEEE Region 10 Humanitarian Technology Conference, R10-HTC 2017, 21 December 2017 through 23 December 2017 ; Volume 2018-January , February , 2018 , Pages 246-249 ; 9781538621752 (ISBN) ; Arasteh, A ; Sarkar, A. K ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
EEG based biometrics using linear Support Vector Machine (SVM) is proposed in this paper. Human identification using electroencephalographic signal was done in this research. Reliability of most of the biometrics systems is not up to the mark because of the possibility of being faked or duplicated. Here, the brain signatures were used as a possible biometric identifier. A Database for Emotion Analysis using Physiological Signals containing 40 trials from each participant was used. International 10-20 system of EEG electrode placement was employed and data from Cz electrode was taken for this research. Some researches showed nice performance with few subjects. Here, 20 subjects were used from...
Modelling and Simulation of Heat Transfer in the Moicrowave Sintering Process of Uranium Dioxide
, M.Sc. Thesis Sharif University of Technology ; Outokesh, Mohammad (Supervisor) ; Mousavian, Khalil (Supervisor)
Abstract
One of the steps in the production of nuclear fuel pellets used in the core of a nuclear reactor is sintering. Sintering means the consolidation of a pressed powder sample into an integrated solid. This process can be done in different ways, such as traditional sintering, microwave, spark plasma, etc. In the process of fabrication of nuclear fuel pellets, after producing uranium dioxide in powder form and making corrections on the size distribution of powder grains, it would be nolded and then sintered. In this research, the temperature evolution of the green pellets introduced to microwave heating were investigated. In this report, a brief overview of the principles of microwave heating is...
Development of a Validation and Calibration Algorithm for Thermohydraulic Sensors of Bushehr NPP First Circuit Using Neural Networks
, M.Sc. Thesis Sharif University of Technology ; Ghaffari, Mohsen (Supervisor) ; Moshkbar-Bakhshayesh, Khalil (Co-Supervisor)
Abstract
Sensors are one of the most vital instruments in Nuclear Power Plants (NPP), and operators and safety systems monitor various parts of the NPP and control transients by analyzing the values reported by the sensors. Failure to detect malfunctions or anomalies in them would lead to catastrophic consequences. A new approach based on thermo-hydraulic simulation by RELAP5 code and Feed-Forward Neural Networks (FFNN) is given to detect faulty sensors and estimate their correct value which are two main objectives of the current study. This approach consists of two main parts; The first part, Fault Detection Hyper Block (FDHB), responsible for detecting faulty sensors, and the second part,...
Estimation Influential Parameters in Operation of the Bushehr Nuclear Power Plant using Neural Network
, M.Sc. Thesis Sharif University of Technology ; Ghofrani, Mohammad Bagher (Supervisor) ; Moshkbar Bakhshayesh, Khalil (Co-Advisor)
Abstract
Given many computing errors in current systems, a method appears necessary for predicting the nuclear parameter quickly and accurately. In this thesis, a neural network was used to predict safety in a nuclear power plant in order to develop an operating aid tool for preventive measures.First, some studies were conducted on appropriate feature selection for training neural networks. Some case studies have also been carried out on parameter prediction through soft computing in a power plant. In the next section, an expert judgment was taken into account to select DNBR (Departure from Nucleate Boiling Ratio) as a criterion for safety evaluation in the exploitation of a nuclear power plant (PWR)...
Estimation of Power Peaking Factor (PPF)Parameter in VVER Reactor Using Soft Computing, Case Study: Bushehr Nuclear Power Plant
, M.Sc. Thesis Sharif University of Technology ; Ghofrani, Mohammad Bagher (Supervisor) ; Moshkbar Bakhshayesh, Khalil (Supervisor)
Abstract
operation of a nuclear power plant. Therefore, constant monitoring of the reactor core with reliable methods is important. To monitor the reactor heart, it is necessary to estimate and calculate some parameters, with high speed and accuracy, such as power distribution inside the heart, reactivity feedback coefficients, PPF, DNBR, etc. Analytical methods are often used to calculate these parameters, which in case of failure of the sensors, the calculations will be practically disrupted, and the method used in this research can solve these problems by losing a small amount of accuracy.In this study using real data of Bushehr nuclear power plant (BNPP) and by soft computing methods and...
PIDEC Batteries Simulation Accompany with Comparative Study of Key Parameters on its Efficiency
, M.Sc. Thesis Sharif University of Technology ; Moshkbar Bakhshayesh, Khalil (Supervisor) ; Mohtashami, Soroush (Co-Supervisor)
Abstract
Nuclear batteries have been attractive since the beginning of the twentieth century due to their longer life in comparison with other types of batteries. These batteries are produced in different types with different efficiencies depending on the method used to convert their energy. In this study, due to the lack of the resources in the country to study the types of nuclear batteries, first we did an overview of the classification and operation of different types of nuclear batteries, especially on the latest type of nuclear batteries, PIDEC, that has not been studied in the country so far. The most important feature of a PIDEC is that it has an intermediate stage to transmit the maximum...
Design and Development of Gamma Wireless Detector with the Use of Soft Computing to Identify the Type of Radioisotope for Environmental Monitoring
, M.Sc. Thesis Sharif University of Technology ; Vosoughi, Naser (Supervisor) ; Moshkbar Bakhshayesh, Khalil (Co-Supervisor)
Abstract
The inability to directly observe radioactive rays, from the beginning of the discovery of these rays, led various people to seek a suitable solution to detect and recognize their properties. To this end, many detectors with different capabilities were built. On the other hand, in the electronic world, it was possible to analyze electrical pulses and extract information based on them. Therefore, some detectors were designed to convert the traces left by the entry and interaction of radioactive rays into measurable electrical pulses proportional to the properties of the incident radiation. Analysis of these pulses provides information about the properties of the incident rays. So far, a...
Failure analysis of a gas turbine compressor
, Article Engineering Failure Analysis ; Volume 18, Issue 1 , 2011 , Pages 474-484 ; 13506307 (ISSN) ; Tirehdast, M ; Masoumi Khalil Abad, E ; Parsa, S ; Motakefpoor, M ; Sharif University of Technology
2011
Abstract
During the shut down period, a 32. MW gas turbine experienced a severe failure accompanied by a loud noise near its second natural frequency at 4200. rpm. After opening the turbine casing, it was revealed that the disks of stages 16 and 17 of the compressor had been fractured and all of the stationary and rotary blades of stages 14-18 of the compressor had been detached from the dovetail region of the disks. The degree of damage was such that repairing the compressor was not economical, and thus, the compressor was no longer able to be used. Diagnostic work was carried out using different finite element models and fractography analysis. Analysis showed that multiple cracks had been initiated...
Diagnosis and Prediction of Coronary Arteries Disease by Applying Data Mining and Image Processing Techniques
, M.Sc. Thesis Sharif University of Technology ; Khedmati, Majid (Supervisor) ; Foroozan Nia, Khalil (Co-Supervisor)
Abstract
Heart disease is one of the major causes of death in all countries, especially developing countries. At the moment, using Image Processing methods as well as analysis of electrocardiographic signals, heart disease is diagnosed with the help of specialists. Applying artificial intelligence and machine learning methods, many studies attempted to provide models that are used to diagnose automatically the heart disease without the need for a specialist and only relying on the past data. But less is done on CTA images of the heart. Hence, in this thesis, a new method for image processing and a Multi Support Vector Machine (MSVM) classification for coronary artery disease detection based on CTA...
Thermal-hydraulic Analysis of Dry Storage Cask of the Spent Nuclear Fuel and Construction of a Prototype Experimental Setup for its Simulation
, M.Sc. Thesis Sharif University of Technology ; Outokesh, Mohammad (Supervisor) ; Mousavian, Khalil (Supervisor) ; Rezaeian, Mahdi (Co-Supervisor)
Abstract
Storage of the spent nuclear fuels is one of the topics of interest in recent years and many researches have been conducted in this field in order to design storage casks for spent nuclear fuels. In this study, thermal-hydraulic analysis of a dry storage cask for Bushehr Nuclear Power Plant spent nuclear fuels is carried out. Geometry of the analyzed cask is taken from a Russian transportation cask TK-13. Drawing of the geometry is achieved with SolidWorks and it’s meshing is completed in Gambit. 3 different cases were considered for cask’s geometry and design: cask without spacers inside, cask with spacers inside, and cask with spacers inside and fins on the outside surface of the cask....
Modeling & Evaluation of Residual Heat Removal System in Bushehr Nuclear Power plant with using the Relap5 system code
, M.Sc. Thesis Sharif University of Technology ; Ghofrani, Mohammad Bagher (Supervisor) ; Mousavian, Khalil (Supervisor)
Abstract
In this study the modeling of low pressure injection system to remove heat from the reactor core of Bushehr nuclear power plant(BNPP) after it has been paid off. After a full assessment of the primary circuit and the Bushehr nuclear power plant emergency cooling system, all the information needed to model the primary circuit and the low pressure injection system and the plant were collected in the available evidence. Then, according to the code, a code RELAP5 standards for light-water reactors(LWR) in steady state and transient parameters termohydraulic is a component of the hydrodynamic and thermal structures suitable for modeling of low-pressure injection system and primary circuit...
Identification and Forecasting of Nuclear Power Plants Transients by Semi-Supervised Method with Change of Representation Technique
, M.Sc. Thesis Sharif University of Technology ; Ghofrani, Mohamad Bagher (Supervisor) ; Moshkbar Bakhshayesh, Khalil (Supervisor)
Abstract
In this work, we aim to find a way to identify and forecast transients in nuclear power plants with the aid of semi-supervised machine learning algorithm. Forecasting and identifying transients in nuclear power plants at the early stages of formation are essential for safety considerations and precautionary measures. The use of machine learning algorithms provides an intelligent control mechanism that, along with the main operator of the power plant, raises the transient detection and identification rate. Our algorithm of choice is to change the way data is presented, which is a semi-supervised learning approach. The algorithm consists of two methods: quantum dynamics clustering...
Nonlinear Modelling of Fluid and Solid Interaction in Shells Conveying Fluid Using Combination of FEM and BEM
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor) ; Kord kheili, Ali (Supervisor) ; Dehghani Firouzabadi, Rohollah (Co-Advisor)
Abstract
In this M.Sc. thesis dynamics of a system of 3-D fluid (internal) and solid interaction hase been studied. Structure (shell) filled with dense fluid (liquid) and it is under large amplitude vibrations excitations. Shell is analized using geometrical nonlinear general shells formulations. The nonlinear analysis includes large displacements, large rotations and large strains without considering material nonlinearity. Based on the potential flow assumption the governing equations of fluid are derived. And using boundary elements formulations fluid hydrodynamic pressure in each step is drived. In order to simultaneous and mutual influence of fluid and structure, numerical model of combined...
Functional compartmentalization in the hemocoel of insects
, Article Scientific Reports ; Volume 9, Issue 1 , 2019 ; 20452322 (ISSN) ; Aviles, J ; Adjerid, K ; Schoenewald, C ; Socha, J. J ; Sharif University of Technology
Nature Publishing Group
2019
Abstract
The insect circulatory system contains an open hemocoel, in which the mechanism of hemolymph flow control is ambiguous. As a continuous fluidic structure, this cavity should exhibit pressure changes that propagate quickly. Narrow-waisted insects create sustained pressure differences across segments, but their constricted waist provides an evident mechanism for compartmentalization. Insects with no obvious constrictions between segments may be capable of functionally compartmentalizing the body, which could explain complex hemolymph flows. Here, we test the hypothesis of functional compartmentalization by measuring pressures in a beetle and recording abdominal movements. We found that the...
Effects of tool rake angle and tool nose radius on surface quality of ultraprecision diamond-turned porous silicon
, Article Journal of Manufacturing Processes ; Volume 37 , 2019 , Pages 321-331 ; 15266125 (ISSN) ; Akbari, J ; Yan, J ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the...
Effects of tool rake angle and tool nose radius on surface quality of ultraprecision diamond-turned porous silicon
, Article Journal of Manufacturing Processes ; Volume 37 , 2019 , Pages 321-331 ; 15266125 (ISSN) ; Akbari, J ; Yan, J ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This paper presents an investigation of the effects of tool rake angle and nose radius on the surface quality of ultraprecision diamond-turned porous silicon. The results showed that as rake angle decreases, the high-stress field induced by the tool edge increases, causing microcracks to propagate extensively near the pore walls. As a result, the ductile-machined areas shrank under a negative tool rake angle. On the other hand, brittle fracture occurred around pores released cutting pressure significantly. These trends of rake angle effects are distinctly different from those in the cutting of non-porous silicon. Finite element simulation of stress in the cutting area agreed with the...