Sharif Digital Repository

Studying the performance of flow meters is of great importance in order to improve their quality. In this study, we are looking for an optimal design for a turbine flow meter in which the measurement accuracy, pressure drop and response speed indices are improved. For this purpose, a turbine flow meter with a diameter of 2 inches has been selected and its performance has been numerically modeled using computational fluid dynamics in a steady and transient state. By modeling the steady state, the measurement accuracy and pressure drop indices are obtained, and by modeling the transient state, the response time of the flow meter is obtained. In order to increase the accuracy of numerical... 

One way to increase the efficiency and improve the performance of a gas turbine is to increase the inlet gas temperature. On the other hand, the inlet temperature has an allowable operating range, and increasing it beyond the tolerance of the alloys used in turbine blades causes structural defects and significantly reduces the blade life. Therefore, to increase the blade life, various cooling methods such as internal and layer cooling are used. Considering the blade geometry and cooling paths, accuracy in the manufacturing process is doubly important in the production of these blades. The importance of this issue is that if the cooling channels produced are inconsistent with the design... 

Increasing in social communication via electronic ways has been made social network analysis of these communications more important each day. One of the most important aspects in social network analysis is community detection in such networks. There are many different ways to extract communities from social graph structure which in some of them the content of communication between actors has been noticed in community extraction algorithm. In this thesis after a short survey over advantages and disadvantages of existing methods for community detection, a new method for extracting communities from social networks has been suggested which in addition to streaming property of data it spot the... 

The standard model of Cosmology (SM), based on Einstein’s theory of general relativity (GR), is the best model in describing the cosmic-scale observations. In galactic scales, however, galactic dynamics show a discrepancy between the observed luminous mass and the predicted value from the theory. Two approaches are suggested to eliminate this inconsistency: assuming the existence of dark matter within the context of GR, or modifying the theory of gravity in galactic scales, like MOND or MOG. In this thesis, we study the spherical collapse and the formation of shell galaxies in MOG, in comparison with SM. We introduce the action and the field equations of MOG and the equation of motion of a... 

The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

Strongly Rayleigh measures are an important class of negatively dependent (repulsive) probability measures. These measures are defined via a geometric condition, called “real stability”, on their generating polynomials, and have interesting probabilistic properties. On one important property of negatively dependent measures is their rigid dependence structure. In other words, the it is impossible for these measures to have strong overall dependencies. In this thesis, we study two manifestations if this phenomenon: (1) paving property and (2) tail triviality. Informally, the paving property states that it is possible to partition the set of the components of every strongly Rayleigh random... 

In this M.S. dissertation numerical study of slinger fuel distributer has been studied. This type of atomizer has been used in mini turbojets like Teledyne CAE.
The main purpose of this work was obtaining spray structure of slinger atomizers. This goal was achieved by implementing a UDF code in FLUENT® software to model the primary atomization that include variation of fluid from exit of slinger disk bores till formation of primary droplet. In FLUENT® the DPM method and its ability to utilizing Lagrangian approaches have been used. The result of this model is validated by the data from experimental test that can be found in Articles. This is the first time that spray structure of slinger... 

The process of injecting acid or acidizing, is one of the most common ways to stimulate oil and gas wells. The purpose of this process is to increase the productivity of the well by increasing the permeability of the reservoir rock around the well. This is especially important in carbonate reservoirs due to damage to the formation and low intrinsic permeability in some places. In order to minimize the effects of structural damage, conventional wormhole channels are created to pass through the injured area. One of the important factors in acid validation is achieving optimal injection rate, which means obtaining the highest permeability with the lowest amount of injected acid.Numerous... 

Electric vehicles (EVs) will be used rampantly in future transportation system. Although the uncontrolled charging of these EVs will be threatening for the stability and sustainability of the grid, a well-suited energy trading policy may provide a number of beneficial services to the grid as well as preserving the sustainability of the system along with heightening the performance of operation. In this paper, by taking advantage of block rate tariff, a wholesale pricing policy is introduced. A multi-objective approach is utilized to address the cost reduction and load levelling services, concurrently, in order to guarantee the profits of the both the grid and EVs. Due to the high... 

In this thesis, consider three important questions in the Iranian Wholesale Electricity Market (IWEM) and answer its. The first one is whether the bidding behavior of the firms in the IWEM has been ex-post optimal? The results of the research show that, on average, the firm’s bidding behavior didn’t optimal in the IWEM, and therefore the bidding strategy of them could be improved. This issue is importance from the regulatory viewpoint in terms of assessing market efficiency and market power of firms, as well as from the firm’s point of view to improve the bidding strategy and increase its profits. The second issue is the assessment of the firm’s ability to exercise unilateral market power by... 

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... 

MQTT (Message Queuing Telemetry Transport) is one of the essential and widely used protocols in the Internet of Things (IoT) networks. It operates at the application layer (Layer 7) for data transmission. As IoT applications using this protocol for communication have grown, securing such systems against security attacks has become a significant challenge. One of the important attacks implementable by IoT networks is Distributed Denial of Service (DDoS) attacks. In this thesis, we initially provide a general overview of IoT security and demonstrate how DDoS attacks disrupt the availability feature in these networks. We then examine known types of DDoS attacks to gain a better understanding of... 

The economic activities in a country involved with depletion of natural resources and emission of pollutants and gases to the environment. Depletion of exhaustible resources and environmental pollutions are two determinants of sustainability of development. The present research work is aimed at studying the sustainability of Iranian economy in 2009. The analysis of sustainable development of economy is based the concept of exergy, exergy efficiency and ecological exergy efficiency. Exergy efficiency is the ratio of the exergy of a product in economic activity to the exergy of input streams to that section of economy. Ecological exergy efficiency is defined as the ratio of exergy of product... 

In this project railway industry is introduced as an optimal alternative for transportation in this country. To select the best choice, four railway technologies that have commercial capacity are presented and the most appropriate one is selected with respect to several criteria, including fuel consumption. The purpose of this thesis is to present the best technology in order to improve Iranian railway transportation by considering the shortage of fossil resources as well as pollution.In this project,the copmparison of alternatives and assessment criteria for best technology selection is done by Analytical Hierarchy Process (AHP) and the questionaries are filled out by industry and... 

In this study, integrated navigation systems that utilize velocity-matching algorithm and are used in automatic landing of Unmanned Aerial Vehicles (UAV) are investigated. At first, the accuracy of the navigation system in the landing phase is analyzed and the relationship between the accuracy of inertial sensors, flight parameters and the accuracy of the navigation system is derived analytically. Then, by integrating the dynamic model of the UAV and the inertial measurement unit, a new algorithm for navigation of fixed-wing UAVs is presented. The integration mechanism of the proposed algorithm is tightly coupled; hence, it is capable to eliminate the errors of UAV model and inertial system.... 

Many lattice-based public key encryption schemes are forced to use long keys. To deal with this problem, structured lattices such as NTRU can be used. Lattice-based searchable public key encryption schemes are no exception. Furthermore, in most existing searchable public key encryption schemes, it is assumed that the user searches documents with only one keyword. However, using a conjunctive keyword search, we can search for documents containing several keywords by executing the trapdoor generation algorithm only once. On the other hand, in most of the published searchable public key encryption schemes, storing and searching encrypted keywords are responsibility of a central entity called... 

The human brain can be described as a dynamic system with multiple subsystems interacting with one another and multi-channel observations of these subsystems are available. The modeling of a system from its observations allows us to gain insight into how its various components interact with one another and also provides intuition about the desired system. Hidden Markov Model (HMM) is a probabilistic model with hidden states that is suitable for modeling these types of systems. Multi-channel observations are available from several subsystems interacting with each other within a general system. In this case, it may be necessary to develop more comprehensive models incorporating multi-channel... 

Sanctions are one of the most important variables influencing Iran's domestic and international decision-making and have had many effects on Iran's economy and politics in recent years. Iran's ability to influence the oil market and harm the interests of the sanctioning countries in this market raises the question of whether such a capability could affect the outcome of sanctions and lead to the withdrawal of those sanctioning countries. A theoretical examination of the issue of sanctions using game theory shows that if the sanctioned country is not able to retaliate in areas other than the disputed issue, the sanctions game may not reach an equilibrium in which the sanctions are lifted but... 

Governments and organizations need to classify network trac using deep packet inspection systems, by protocols, applications, and user’s behavior, to monitor, control, and enforce law and governance to the online behavior of its citizens and human resources. The high capacity of machine learning in the classication problem has led trac monitoring systems to use machine learning.The development of machine learning-based trac monitoring systems in the eld of research has reached relative maturity and has reached the border of industrial, commercial and governmental use. In the latest trac classi-cation studies using neural networks, as the most ecient machine learning methods, the classication...