Sharif Digital Repository

Recently wind turbines with vertical axis attract attention of world’s scientific society to itself because of many reasons such as: ability to work in areas with high turbulency, structural simplicity, independency from wind direction, easy maintenance and low capital cost. So that major part of recent researches in context of wind turbines are about these turbines. In this project a small sample of wind turbine from darrieus type have been designed, manufactured and finally important parameters such as Pitch Angle, Blade numbers and Aspect Ratio have been investigated. Darrieus turbine with 4 Blades and Pitch Angle of +15° was the most appropriate sample between the test samples. In the... 

The necessity of electrical energy, high cost of big power plants and high voltage transmission lines and also progressing of restructuring science has lead to the increasing of tendency to use the distributed generation in electrical industry. Among of different types of distributed generations, fuel cell power plants because of many advantages such as high efficiency, low emission, modular structure and ect., have a high potential to be used in power systems. The fuel cells produce electrical energy by chemical reactions. Due to the necessity of having the knowledge related to the chemical reaction which are effective on fuel cell, to study the fuel cell performance, this type of... 

Simultaneous planning of project scheduling and material procurement can improve the project execution costs. Hence, the issue considering this approach that each activities requirement can be distributed on the duration of it, has been addressed here by a mixed-integer programming model (named model 2). The proposed model facilitates the procurement decisions by accounting for a number of suppliers offering a distinctive discount formula from which to purchase the required materials. This paper proposed a genetic algorithm combining with a heuristic method to deal with the problem. The underlying factors of the solution methods are calibrated by the Taguchi method to obtain robust... 

Today, for construction of UAV, designers are interested in and trying for substitution of composite material instead of metal. They would rather use composite structures due to lower costs of construction, availability, along with high ratio of strength to weight of this material, while metal structures are mainly rare and too expensive for construction of UAV. For instance, unavailability of aluminum metal and complicated methods of construction of aluminum wings with using of special tools, justifies using of composite with easier construction, abundant, and cheaper materials. The main goal of this project is redesign of aluminum wing of a jet engine UAV, In fact, by doing some structural... 

Semi-automated Continuous Speech system deals with collecting corpus speech. It has very different problems in various natural languages because of different types of speech, and collecting speech corpus containing continuous word is very time-and- cost consuming. To overcome this problem, human-based computing techniques are proposed to collect speech corpus. In this thesis, we describe influencing factors in collecting steps of continuous speech and provide a description of human-based techniques to solve problems specially collecting of continuous speech. To collect speech corpus using human-based techniques, a game has been used so that speech corpus of web users are collected during the... 

Nanopositioning is a technology for moving a target object within nanometer (10-9 meter) resolution. Nowadays nanopositioning stages have emerged as an important technological advancement in hi-tech applications, including scanning probe microscopy, lithography, nanometrology, fabrication and assembly of nanostructures and beam steering for optical communication systems. To achieve nanometer resolution the stage must focus on a few tens of micrometers travel range. The combination of piezoelectric actuators and monolithic compliant mechanisms can provide a smooth motion without friction, wear, and backlash. So, piezo-driven compliant mechanisms are used widely in nanopositioning systems. The... 

Acidizing is one of the widely used practices of formation damage remediation. The success of this rather expensive job depends on the precise design and operation. Though, improper execution of an acid job, not only does not improve the formation damage but also can contribute to even more damage itself. For this purpose, it is critically important to thoroughly design an acidizing job conducting extensive lab experiments and utilizing numerical tools before operation in order for a successful acidizing. Unlike, carbonate acidizing, the chemistry of sandstone acidizing is very complex and challenging because of the wide variety of minerals and aqueous species present in the system. Hence, a... 

In this research, a pricing-inventory model with multiple interdependent products and stochastic demand is studied. In the relevant literature, there are many researches that are related to optimize the inventory or price independently and also optimizing joint inventory and pricing for single product. But joint optimization of inventory and pricing for multiple interdependent products is relatively new and still there are many potential research gaps in this area. We develop the model with additive and multiplicative demand uncertainty. Then we develop a genetic algorithm and tune its parameters to solve the models. We investigate the efficiency of proposed GA. Results were relatively good.... 

The ambiguity in the meaning of scientific explanation has caused the philosophers to use different criteria for differentiating it from other explanations. One of the most important of these criteria is Salmon’s criterion. According to Wesley Salmon, a scientific explanation is an objective issue and it is far beyond descriptive knowledge which can be found out about the world. The index provided by Salmon for explanation as a scientific interpretation is based on two principle foundations: 1. Statistical relevance 2. Causal relation. It would be a key to understand the world better. In this paper, first, we will argue that the explanation has both objective and subjective components and... 

In this research, the instability analysis of single-walled carbon nanotubes (SWCNTs) and graphitic shells conveying fluid is investigated based on the molecular structural mechanics. Using the reduced order models for fluid and structure, the dynamic behavior of carbon nanotubes (CNTs) conveying fluid is accurately modeled via a few number of lowest flow modes and natural frequencies and mode shapes of CNTs structure. In addition, the boundary element method (BEM) is used to model the potential flow. The molecular mechanics (MM) model is applied to modal analysis and driving the natural frequencies and mode shapes of SWCNTs. The effect of chirality on flow-induced instability is taken into... 

Double channel and coreless induction furnaces are used extensively in many processing industries due mainly to their good heating efficiency, high production rate, clean working environments and relatively low operating costs. The study of heat transfer treatment and evaluation of the heat losses of these furnaces becomes an important issue in melting industries. In this dissertation, a heat transfer analysis will be performed for an induction furnace and heat losses by conduction, convection, Eddy-Current and Hysteresis in a furnace structure, and radiation from the body of a specific induction furnace will be modeled considering the symmetry of the furnace chamber. The models presented in... 

Leakages in the transmission pipes include a large proportion of water loss. Scarcity of fresh water in one hand and high costs to compensate for drop in pressure and flow lines, on the other hand, detection and location of leaks have been important. This phenomenon can also cause a lot of damage to the urban contextures. This thesis considers the leakage in tubing buried in the soil by means of a floating robot. Since the rate of leakage, specifies the requirement to perform maintenances, In addition to finding the leakage, an overall estimate of the amount of leakage is desired.Since non-destructive leak detection is desired, the mechanical-magnetic sensor is designed. First, for the... 

In this thesis, Model reference adaptive control in fractional order systems was discussed. Various types of this problem can be introduced based on fractional order dynamics in system equations, reference model equations or adaptation laws, which some of them play more important role in real-world applications, also some of them have more complexity in governing mathematical equations and in stability analysis. Fractional order dynamics were recently used in many real-world applications like model reference control, Chaos synchronization and Chaos control, so studying adaptive control in this fields, could be important. Nowadays, Model reference adaptive control was used in many industrial... 

High resolution and low power analog to digital converters are used in wireless communication receivers, Sensor Networks and Medical Instrumentations. Reducing power consumption at a high conversion rate is one of the most basic challenges for these converters. Pipelined SAR structure is considered for 40-50 MS/s and 10-12 bits, and is of interest because of consuming low power and using a small area. Besides using Pipelined SAR structure, circuit level and system level modifications are also proposed to decrease the power consumption. The ADC is designed in 0.18µm CMOS technology with 1.2v supply voltage. The results show 4.5mW power consumption, when ENOB is 11.04bit, which is very low... 

Pulse tube refrigerator due to the relatively high efficiency, high reliability of linear compressor and the absence of moving parts in the cold area is known as one of the best options to generate up to one kW of cooling power at temperatures from 4 to 123 K. More recently, the use of the device at a temperature of about 150 K, makes use of it even outside of cryogenic temperature. The most important part of the device is regenerator, so understanding the nature of the flow and interaction of gas and solid network in the retrievers is necessary. In this study, Inertance pulse tube refrigerator (IPTR) is simulated using Ansys Fluent in two different conditions. In the first condition the... 

The huge capability of high resolution satellite imageries (HRSI), that includes spatial, spectral, temporal and radiometric resolutions as well as stereoscopic vision introduces them as a powerful new source for the Photogrammetric,Remote Sensing and GIS communities. High resolution data increases the need for higher accuracy of data modeling.The satellite orbit, position, attitude angles and interior orientation parameters have to be adjusted in the geometrical model to achieve optimal accuracy with the use of a minimum number of Ground Control Points (GCPs). In order to obtain high resolution and definition imaging for many applications including surveillance, target tracking, and...