Sharif Digital Repository

The ultimate aim of this research is optimizing high- performance Horizontal Axis Wind Turbine (HAWT) associated with using Computational fluid dynamics (CFD) to predict the flow behavior over wind turbine blades. Computational prediction of the flow over wind turbines is a challenging numerical problem because of the complicated aerodynamics and large variation in length scales. Phenomena such as; the unsteady flow, vortex shedding of the blade tips, flow separation, complicated blade geometry due to variable twist and chord and changes in angle of attack, and highly turbulent flow over blade sections makes CFD prediction challenging, as well as interesting. The goal is to gain an in depth... 

Using clean and renewable energy as driving force for vehicles is becoming more and more important because of rising fuel prices and also environmental concerns. Using solar and wind power for direct use in vehicles seems impractical with today’s technology. Compressed air can serve as an intermediate medium to store energy and utilize it for running vehicles. The main purpose of this research was to conceptually design an air driven vehicle with acceptable performance in a city for everyday life. After a brief history, at first step advantages and disadvantages of using air as driving force of vehicle is studied. This study was carried out in different categories including cost, capability... 

Radar is a type of active remote sensing instrument that is used to create images of an object, such as a landscape. Synthetic Aperture Radar or SAR is another type of radar which is typically mounted on a moving platform such as an aircraft or a spacecraft and uses the motion of the antenna over the target region to provide finer spatial resolution than is possible with conventional beam-scanning radars. In fact SAR is an advanced form of Side-Looking Airborne Radar (SLAR). The movement of SAR antenna acts as another form of aperture; this aperture combined with the physical aperture of the antenna creates a large "synthetic" antenna aperture (the "size" of the antenna) which enables higher... 

This thesis proposes a novel method for enhancing the speech signal based on compressed sensing. Compressed sensing, as a new rapidly growing research field, promises to effectively recover a sparse signal at the rate of below Nyquist rate. This revolutionary technology strongly relies on the sparsity of the signal and incoherency between sensing basis and representation basis. Exact recovery of a sparse signal will be occurred in a situation that the signal of interest sensed randomly and the measurements are also taken based on sparsity level and log factor of the signal dimension.
In this research, compressed sensing method is proposed to reconstruct speech signal and for noise... 

Medical images contain human body pictures and are widely used for diag-nosis and surgical purposes. Compression is needed for medical images for some applications such as profiling a patient's data or transmission systems. Due to the importance of the information of medical images, lossless or visually lossless compression is preferred. Lossless compression mainly consists of transformation and encoding steps. On the other hand, hardware implementation of lossless compression algorithm accelerates real time tasks such as online diagnosis and telemedicine. Lossless JPEG, JPEG-LS and lossless version of JPEG2000 are few well known methods for lossless compression. In this thesis, we introduce... 

This study seeks to compare the effect of curing conditions in the sea, coast, and middle of the island environment on five mix designs of alkali-activated concrete (AAC) based on ground granulated blast furnace slag (GGBFS) and fly ash (FA) and the effect of the ratio of sodium silicate (SS) to sodium hydroxide (SH) and alkali activated solutions (AAMS) to the binder on mechanical properties. The compressive strength and load-deflection test was conducted to obtain uniaxial compressive strengths (UCS), modulus of elasticity ("E" _"S" ), elastic and ultimate strain, and dissipated energy. The most significant decrease in strength was observed in the coastal area and the sea. Also, the... 

Normal aggregates are replaced by polystyrene beads (EPS) due to their low unit weight. EPS concrete is known for its low density and environmentally friendly properties apart from having various pros such as better heat and sound isolation, affordability, and ease of construction. EPS grain size can also affect the compressive strength, and the tensile strength of EPS concrete compression is also inversely related to EPS grain diameter. The EPS concrete has four different percentages of EPS; 0%, 25%, 50%, and 75%. Each EPS percentage has six different unit weights; 15,20,25,30,35 and 40 kg/m3. In the present study 19 different types of mixing designs were used, the one with no EPS beads has... 

The interface behavior of rock-concrete joints and between concrete layers influence the behavior of concrete dam structures. In this study, a modified direct shear test (DST) was implemented in the laboratory to evaluate the interface behavior between 1) rock and conventional vibrated concrete (CVC), 2) rock and roller compacted concrete (RCC), 3) CVC and RCC and 4) two layers of RCC. Two series of in-situ shear tests were also carried out on rock-concrete joints. The friction angle and adhesion for all tested interfaces were determined and analyzed. The effect of uniaxial compressive strength (UCS) of concrete on the interface behavior was determined. Additionally, the effect of surface... 

The benefits of fiber reinforced concrete (FRC) have been thoroughly investigated. Much of this work has focused on polypropylene FRC notched beams. Data on the bending behavior of beams with side notch is scarce. A pilot investigation on the compressive behavior of macro-synthetic FRC and on the splitting tensile strength of FRC was carried out. Twenty beam specimens with two different strength of 35 and 60 MPa was tested. The beams dimensions were 15*15*55 centimeter and they were notched at the bottom at mid and side span. Two different notch depth of 5 and 7.5 centimeter was implemented. At the end it was found out addition of fiber decreases compressive strength of 35 Mega Pascal... 

Due to the diameter and size of nanoparticles, they have been applied in various fields to make materials with better properties. In this thesis, the purpose has been to investigate the influence of nano alumina and nano alumina incorporating nano silica particles on mechanical properties of cement mortars. Different portions of nano alumina that include 1, 3, and 5% have been used. Nano silica with 1 and 2% has been used. At first, nano particles were dispersed by sonication with water, and then the cement mortars with various percent of nano additives with the same workability have been made. After different curing periods (7, 28 days), the specimens have been tested for bending and... 

Recent investigations on construction engineering have determined that repairing of Reinforced Concrete (RC) by means of fiber reinforced polymer (FRP) composites is an effective method of retrofitting existing columns. The main research in this thesis focuses on the repair of concrete specimens which are damaged and their initial strength has been reduced. To achieve this purpose, through experimental procedures, the effect of confining damaged concrete cylinders by FRP, has been investigated. The experimental program included three parameters: type of fibers (glass or carbon), type of confining (full or partial), and the number of layers. First concrete cylinders were made and loaded to... 

In recent years considerable effort has been made to advance the hardware Artificial Neural Networks where in most cases, many neurons are placed on a VLSI chip. This research attempts to build individual neurons and connect them to build a hybrid of analog and digital neural network. In fact, every neuron is an AVR microcontroller which has a number of inputs and outputs. The data transfer between neurons are done by both analog (PWM- ADC) and digital (UART). In the first part, the necessary voltage source and programmer and how to build are discussed. Next A\D convertor, PWM technique, UART and their usage in this project are demonstrated. After that, the neurons are calibrated to improve... 

In analyzing the structural organization of many real-world networks, identifying important nodes has been a fundamental problem. The network centrality concept deals with the assessment of the relative importance of network nodes based on specific criteria. Central nodes can play significant roles on the spread of influence and idea in social networks, the user activity in mobile phone networks, the contagion process in biological networks, and the bottlenecks in communication networks. High computational cost and the requirement of full knowledge about the network topology are the most significant obstacles for applying the general concept of network centrality to large real-world social... 

This thesis proposes a novel method for enhancing the image signal based on compressed sensing. Compressed sensing, as a new rapidly growing research field, promises to effectively recover a sparse signal at the rate of below Nyquist rate. This revolutionary technology strongly relies on the sparsity of the signal and incoherency between sensing basis and representation basis. Exact recovery of a sparse signal will be occurred in a situation that the signal of interest sensed randomly and the measurements are also taken based on sparsity level and log factor of the signal dimension. In this research, compressed sensing method is proposed to reduce the noise and reconstruct the image signal.... 

Concrete is one of the most widely used building materials. Compressive strength of concrete is the most important property in designing reinforced concrete structures. Compressive strength test should be carried out on specimens with standard dimensions. In practice, dimensions of structural elements could be different from the dimensions of standard specimen. The dimensions’ ratio influences the strength of concrete specimen and the coefficient of strength variation. In the present study it is tried to obtain a meaningful relationship between size and strength based on the results of the tests on the specimens with different dimension ratios. Specimens examined in this study are C25 grade... 

Wireless Sensor Networks (WSNs) are comprised by number of sensor nodes, which collect data and transmit them to the sink node, the battery of sensor nodes is limited and this issue appeals the attention of researchers to attempt to improve the energy consuming of sensor nodes in order to prolong the lifetime of networks. Circumstance of routing affects the lifetime of network. Researches have proved the efficiency of Clustering in routing protocols in WSNs. It is notable that the importance of CH selection is undeniable. In this thesis we have worked on the CH election and CH rotation of hybrid method, which utilizes Compressive Sensing (CS) in inter-cluster transmission. We have proposed... 

With the proliferation of Internet-based applications and malicious attacks, security has become one of the most influential aspects in the network and, it should be considered from the beginning steps of designing the network infrastructure. Based on the fact that pattern matching is considered as one of the most important roles of security devices or applications, it becomes an important procedure in firewalls that have been classified as security equipments which adopt a security mechanism in order to restrict the traffic exchanged between networks and particular users or certain applications. While the trend of using compressed traffic is drastically increasing, this type of traffic is... 

Wireless sensor networks (WSNs) consume energy for their sensing, computation, and communication. To extend the lifetime of the network, sensor nodes are equipped with energy storage devices. Recharging their batteries is impossible in most applications. Therefore, energy consumption needs to be monitored and be limited to extend the high performance operation of the network. In this network, the communication module consumes the highest amount of energy. While several methods are proposed to reduce the energy consumption, data compression is one of the most effective ways for energy management by reducing the number of bits to be broadcast. To determine the energy efficiency of the... 

Reducing interconnection costs on chip and power consumption are important issues in designing processors. In a processor, a significant amount of total chip power is consumed in the interconnection. The goal of this research is to find a way to reduce power consumption in the interconnection. In this project we propose a new data sending method in which an LZW-like compression algorithm is exploited to compress data before sending it over the interconnection. Then, the codes of the compressed data are sent through the interconnection in order to reduce the number of dynamic cycles. The simulation results show that using this method can reduce 52% of dynamic power consumption  

Wireless sensor networks (WSNs) are tiny devices with limited computation and power supply. For such devices, data transmission is a very energy-consuming operation. Data aggregation eliminates redundancy and minimizes the number of transmissions in order to save energy. This research explores the efficiency of data aggregation by focusing on different aspects of the problem such as energy efficiency, latency and accuracy. To achieve this goal, we first investigate data aggregation efficiency with constraint on delay, which can be compatible with other important system properties such as energy consumption and accuracy. By simulation, we will show that, depending on the application, we can...