Sharif Digital Repository

Reinforced concrete is one of the most important structural materials used in the construction industry worldwide. Nevertheless, certain physical and chemical factors in the service environment can contribute to its deterioration and failure. One of the most significant factors is the reinforcing steel bar (rebar) corrosion. In order to minimize the rebars corrosion, different kinds of coatings were investigated and evaluated by scientists. In this investigation comparative studies were performed on two different kinds of coated rebars (zinc-rich epoxy and polyamide epoxy coated rebars) and uncoated rebar. In order to evaluate these reinforced concretes, the adhesion, durability, thickness... 

In this thesis, a model is presented to detect and monitor the rotor bar's condition of large motors. This proposed model uses two diagnostic methods MCSA and ZCT, to extract the fault components. The input of the proposed model is only the motor current at two levels of 80% and 100% of the nominal motor load, which by using the two methods MCSA and ZCT and making changes in how to use them can be the disadvantages of other methods such as incorrect detection of rotor bars in Large motors with variable load, the harmonical stator voltage (or the presence of the drives) and asymmetric conditions. The extracted components are classified using two learnable algorithms, the k-NN algorithm and... 

Production logging consists of running measurement instruments called logging tools into an oil or gas well to measure various parameters such as temperature, flow velocity, pressure, density, etc. The primary purpose for production logging is to allow enhancing production profits and decreasing costs. Nowadays the common way for fluid density measurement as a part of these tools depends on radioactive source. Special considerations must be taken upon the use of this principle due to its radioactive character. This thesis is focused on a non-radioactive method of determining density. The subject of this thesis is to consider methods for measuring density based on principle of acoustic... 

The problem of joint design of transmit code and receive filter is considered in many application scenarios of multiple input multiple output (MIMO) radar systems. The performance of the joint design problem is evaluated with the signal-to-interference ratio (SINR) metric in the presence of noise. In such problems, the optimization problem is to maximize SINR on the receiver side with the constraints that are applied on the transmitted waveform. Our proposed method, RTR, is a manifold-based geometric method that performs better than the SDP method in terms of algorithm execution speed and calculation complexity. For simulation, we took sampled and real TIR with Target Aspect Angle (TAA) in a... 

Sonic and ultrasonic measurements are used for checking status of wells. Well logging is used to estimate well specifications like borehole diameter, casing thickness, cement bond quality and cement sheath thickness. In this thesis, some reported works in field of sonic/ultrasonic measurement of oil wells are reviewed and results of software implementation of ultrasonic measurement with pitch-catch arrangement, pulse-echo arrangement and phased array arrangement are presented. ultrasonic measurement with pitch-catch arrangement uses one transducer for transmitting ultrasonic waves and two transducers (in different distances) for receiving ultrasonic waves. Ultrasonic measurement with... 

In the oil industry, a better understanding of the well condition leads to improve the management and increase the oil production. Production logging tools is a set of tools for measuring different parameters such as density, diameter and flow in oil and gas wells. These tools are considered among high-tech tools in the oil industry. The reason is that they should work in harsh conditions, i.e. high temperature about 170 ° C and pressure around 15000 psi, and at the same time give an accurate measurement of the quantity. Current production-logging tools measure the fluid velocity and the diameter of an oil well by individual mechanical tools, and the density by a radioactive densitometer. ... 

Most of the time there are three different materials in oil wells; Oil, water and gas. Measuring volume percentage and flow of the individual materials (phases) is an important issue, due to their critical role in extraction process control. Measuring tool should be able to measure flow and percentage of each phase in a case that they are separated (in deviated wells due to gravity). In addition, the measurement should be carried on in a high temperature and high pressure environment and in presence of corrosive substances. Most of previous researches on Multi-Phase Flow Meter (or MPFM) led to mechanical methods to measure flow and they usually use electrical impedance or permittivity for... 

This study aimed to investigate the efficiency of machine learning algorithms in capturing the dynamics of water particles' age distribution and in estimating the time series of median travel time (MTT) in river basins. The mechanism of solute transport in a catchment does not follow the hydrograph shape of the catchment and depends on the spatial and temporal distribution of solute resident time. The equations governing the age dynamics of water particles discharged from a catchment have been presented analytically in recent research. These equations showed that the transfer of solutes depends on various factors, including climatic conditions, basin topography, and basin vegetation. Also,... 

OFDMA multi-hop cellular network (MCN) is the topic of a wide range of research today. In this thesis, we analyse this type of networks, regarding shadowing status, mobility patterns and different service requirements. In the multi-hop (MH) scenario, six fixed relays are set up in each cell, which split the cell into seven subcells. For mobility modeling, each subcell is split into several sub-regions. Mobile nodes are able to maintain at each sub-region with a random time distribution and migrate from it to one of its neighboring sub-regions. We also consider three types of services requiring specific number of subcarriers with specific BERs. The set of subcarriers is distributed among... 

In this thesis, we evaluate the maximum stable throughput of a cognitive multi-hop IEEE 802.11-based WLAN overlaid on a cellular network. In the considered scenario, the secondary users operate in the downlink or uplink frequency band of primary network and transmit their data in free primary channels using OFDM technique. The activity of primary nodes is modeled independently by ON-OFF alternating states. To model the scenario, each secondary user is modeled with an open queueing network. The queueing network can model the transmission of data as well as the effect of primary users. By writing the traffic equations of the queueing network and applying the stability conditions, we are able... 

In this thesis, we propose two new network coding-based packet relaying schemes suitable for multiple unicast scenarios in a random access network. In such networks the channels may have memory dependent upon the random access scheme. Thus, the optimal scheme for memoryless channels reported recently in the literature is not necessarily optimal in random access networks. In our proposed schemes, we convert a multiple unicast scenario to a combination of multiple anycast and a few multicast scenarios. By such an approach, we exploit the channels between relay node and the other nodes, instead of using only one channel at each packet transmission, for as many as possible. By simple analytical... 

In this thesis the effect of frame aggregation mechanism in maximizing throughput in Wireless Local Area Networks (WLANs) have been investigated. Frame aggregation has become a part of the IEEE 802.11 standard as the amendment IEEE 802.11n. First, we have a quick review on access control layer in IEEE 802.11 standard then illustrate the necessity of frame aggregation. Afterwards, we propose an analytical model for the analysis of an IEEE 802.11n network comprised of an Access Point (AP) and several conventional nodes, all in the coverage area of each other. This analytical model focuses on downlink throughput; therefore only AP uses frame aggregation and the other nodes use basic IEEE 802.11... 

In cognitive radio networks, secondary users try to use empty channels that primary users provide for transmitting data. First, the secondary users sense the target channels. If the selected channel is empty, they send their data. When the primary user returns, the secondary user has to find another empty channel for transmitting data. The process of changing channel is called hand off. In recent years, there are challenges in the spectrum mobility of for reducing delay time of secondary users packet. In this thesis, we assume that the secondary users network is an ad-hoc network. We use contestation based method for reducing collision between secondary users. In this thesis, we present an... 

Car accident damages take about 7 percent of GPD of Iran every year. As a result of car accidents, the economy of the country is damaging irreparably. The amount of road casualties equals casualties in a complete war. Considering the aforementioned conditions, the researchers are thinking about new technologies to reduce the cost of the accidents. So the use of Vehicular ad-hoc Networks (VANET) is inevitable in the near future. Content distribution service is one of the emerging services of VANETs. This service is used in both safety and comfort related applications. Content distribution describes delivery of media content such as Video, Audio, Image, Text, Software, and Video Games over... 

In this dissertation, we focus on two types of EH cooperative networks. In the first type, the source and relay nodes access a shared channel according to a random access protocol. Also, they harvest energy from non-RF environmental resources. The relay node has data and energy buffers to store the packets of the source and the harvested energy, respectively. Our main goal is to find the optimal relaying protocol at the relay node. In this regard, the first type of the EH cooperative networks are investigated in two different scenarios. In the first one, the MAC channels of the nodes are independent of the applied policy at the relay node, and thus the throughput of the network is fixed.... 

Cooperative networks have attracted much attention in the last decade. Being introduced to mitigate the inefficiencies in the physical layer, cooperation can also be beneficial in upper layers, such as MAC layer. Using cooperative communications is specifically more challenging in the random access networks, where collision is a main concern. Delay, as one of the main performance metrics in random access networks, can decrease significantly by using cooperative communications. Transmission delay, i.e., the required time for delivering one packet form its source to destination, is an important metric in many communication networks, such as the networks in which each node generates and... 

In this thesis, we investigate the age of information in multisource networks. To this end, in the first phase of this thesis, we evaluate the Age of Information (AoI) in slotted ALOHA network. Regarding the interactions among the nodes in such a network, we model the memory of this network with a Trellis and find the peak Age of Information (PAoI) by using this Trellis. Then, we evaluate Age of Information-constrained regions and achievable throughput regions in the slotted ALOHA network and optimize Age of information in a symmetric case. In the second phase, we propose an efficient prioritizing scheme from AoI point of view and find the distribution of AoI and PAoI in such a scheme with... 

In data transmission from a transmitter to a receiver, in some applications receiving updated data is crucial. To this end, a metric called Peak Age of Information has been introduced, the minimum of which is equivalent to having more updated packets. In this thesis, a method for calculating the probability distribution function of this random variable in a random access network with a transmitter, a relay, and a receiver in which the error probability of the channels between the transmitter and the relay and also the relay and the receiver is less than the error probability of the channel between the transmitter and the receiver, is proposed. The transmitter and the relay send their packets... 

Today, with the proliferation of smart devices and the advent of various innovative applications, there has been an exponential surge in the number of users in telecommunication networks. Consequently, the data traffic rate is escalating considerably. This has created a major predicament for wireless networks due to the limited frequency spectrum. Therefore, the conventional centralized architecture makes it difficult for the network to address these numerous simultaneous requests. This issue can be solved by designing new architectures. In a way, network information is disseminated to the network's periphery and the contents of the primary data center are provided temporarily in closer...