Sharif Digital Repository

Traffic volume is the most important characteristic in most traffic studies, which is regularly measured by sampling methods for a given road. Traffic volume has determining effect in specifying network origin-destination demand, improvement of roads, traffic distributions over the network, improving road parameters, air pollution and in other aspects of flow in the network. There are many ways to measure traffic volume in different situations. However, most of them are expensive to implement and in cases which take a long time to do the survey, or the number of locations are excessive, the operation would not be cost-effective. In this research we investigate using macroscopic... 

In this thesis the problem of spacecrafts formation control for halo orbit around the second libration point (L2) of the Sun-Earth Three Body (TB) system is investigated. Station keeping, reconfiguration and precision formation control of spacecrafts on halo orbits are performed via the use of the nonlinear Integral Sliding Mode (ISM) method, optimal closed loop Linear Quadratic regulator (LQR) approach as well as the Model Prodective Control (MPC). In this regard the nonlinear relative dynamics of deputy-chief spacecrafts are derived within the concept of both circular and elliptical three body problem; as well the perturbation model of the Moon and the linear model of restricted three... 

The extensive use of nonlinear loads such as motor drives and new generation of home appliances has caused a deterioration of power quality in power systems. The use of active power filters due to the fast variation of the loads has been recommended by power engineering. In this method, the harmonic profiles are controlled by applying active filters in a distribution feeder. Optimal placement of active filters in a distribution system due to the increase of harmonic generation loads has attracted researchers. However placement of each filter is the major concern that researchers face. In this paper, a new objective function is introduced to determine the optimal number and location of active... 

Keyword spotting with high speed and accuracy is an important subject whithin speech processing domain especially when we are dealing with various transmission channels. In this research discriminative keyword spotting methods are compared with HMM-based approaches. We have employed the discriminative approaches as our baseline methods due to their higher accuracy. The drawback of the conventional discriminative methods is their high computation cost and long execution time. The discriminative approach consists of two steps: feature extraction and classification. We have proposed four ideas to improve the performance of the baseline method. To improve the speed of the process, in feature... 

The demand for independent power generation has been increased in recent years due to the growing demand in distributed networks, losses and power qaulity in power systems. These losses occur in transmission to distribution networks from the generation sites to the end-user loads which have harmonic losses besides fundamental losses.. The non-linear load makes the harmonics flow in the line and create the harmonic losses. However, in a distributed network with several DGs of different types and with all kinds of variable nature loads, an optimal power balance in the system has to be achieved. This optimal objective, which results in minimal energy losses over a specific period of time,... 

One of the most intrinsic challenges of flash-based Solid State Drives (SSDs) is erasebefore-write limitation and the limited endurance of flash chips. Wear leveling and garbage collection are two mechanisms implemented in SSD’s controller to enhance endurance and performance. While wear leveling attempts to distribute erasures across all blocks in an even manner, it imposes a new security challenge on SSD,which leads to the presence of invalid data blocks in flash chips. Therefore, some data blocks that are logically deleted by the user are still available in flash chips and can be recovered by software or hardware recovery tools.
In this paper, a new criteria named vulnerability time... 

The need for independent power generation has been increased in recent years with the growing demand in micro grid systems. Losses in power systems are unavoidable. These losses occur in transmission to distributionnetworks from the generation sites to the end-user loads. Reduction of power losses has been one of the reasons for engineers to be attracted by micro grid systems which include small size independent power generation units. However, in a micro grid with several DGs of different types and with all kinds of loads of variable nature, an optimal power balance in the system has to be achieved. This optimal objective, which results in minimal energy losses over a specific period of... 

This dissertation studies the operation of the power sharing system in a micro-grid (MG) which includes a synchronous generator and the converter based distributed generation (DG) units. Increasing advent of MGs and the huge penetration of DGs to the existing power systems require comprehensive studies on the interactions between synchronous generators and converter based DGs for the sharing of power during and after the occurrence of different disturbances such as load changing. Thus, this project discusses existing control methods which can be used to share the power between a synchronous generator and converter based DGs. Then, a new control strategy is proposed in order to enhance the... 

Uncertainty-based Multidisciplinary Design Optimization (UMDO) is a growing approach in design of complex engineering which has been of great interest to many design bureau and research center especially in field of aerospace. The UMDO goal is to achieve a global optimum design using effective disciplines, interdisciplinary relations and appropriate uncertainty modeling. In this regard, choosing main analysis, design discipline, uncertainty modeling and their content fitness, formulating the problem structure, interaction of disciplines, modeling level of fidelity and the optimization method are the most important challenge of the MDO problem so UMDO is a new trend of MDO, and have been the... 

This thesis is focused on flight dynamics modeling and analysis of an articulated Flapping Micro Air Vehicle (FMAV), where the articulating joint is placed near the wing mid chord span. The articulation modeling, its results and verification due to added degrees of freedom are considered the key motivation and novelties of this project. Initial analyses indicated that a simple articulation device such as joint is not appropriate and will not be efficient for flying FMAV. As a corrective action, a spring-damper mechanism was utilized beside the articulation. Subsequently, the kinematics’ equations are developed and verified using the MSC Automated Dynamic Analysis of Mechanical Systems... 

Rapid growth of space traffic and small satellite systems for current and future space missions have generated new enhanced performance requirements for navigation subsystem. As such, the navigation subsystem is considered as a vital part of all active satellite systems that effectively influences their successful missions. In this regard, the present work is dedicated on the subject of autonomous satellite navigation utilizing nonlinear filters, for which some laboratory experimentations have also been implemented. Generally, advanced orbit and attitude estimation algorithms can effectively compensate for the effect of low cost hardware and sensor packs utilized in microsatellites. In... 

Propulsive efficiency of flapping wings is optimized via a combination of flapping and elastic wing behavior. In this thesis, a complex complete model of flapping air vehicles (FAV) is developed in order to simulate the wing aeroelastic behavior. The resulting model is in the form of a complex set of partial differential equations whose solution is only numerically possible. Using the resulting simulation model, the different flapping behavior of the right and left wings can also be evaluated along with the resulting forces and moments that make the FAV flight realizable. One of the key flight conditions considered in many simulations is that of cruise flight. In order to have a... 

Today Ethernet is the predominant technology for implementing Local Area Networks. Its privileges encourage service providers to extend Ethernet from Local Area Networks to Metropolitan Area Networks or even Wide Area Networks. Ethernet benefits such as low operational costs, well interoperability, plug-n-paly characteristic and rapid provisioning on demand make Ethernet ideal for Metropolitan Area Networks.But Ethernet by itself has some weakness like flat structure that makes it unfit for use in Metropolitan Area Networks. A suitable solution for taking advantages of Ethernet benefits in service provider network is using Ethernet in access network and applying multi-point to multi-point... 

Statistical approaches (purely statistical and model-based) are the most efficient methods in single-channel speech enhancement. Despite these efficiencies, the problem of speech enhancement is still a challenge. Recent researches which propose univariate non-Gaussian distributions are more appropriate for speech signal in different domains. Based on these univariate distributions, statistical approaches have been modified and consequently better results have been reported. The purpose of this thesis is speech enhancement based on hidden Markov model using multivariate non-Gaussian distribution. The results of speech enhancement algorithm based on hidden Markov model in DCT and DFT domains... 

Statistical parametric speech synthesis (SPSS) has dominated speech synthesis research area over the last decade, due to its remarkable advantages such as high intelligibility and flexibility. Decision tree-clustered context-dependent hidden semi-Markov models are typically used in SPSS to represent probability densities of acoustic features given contextual factors. This research addresses four major limitations of this decision tree-based structure: (a) The decision tree structure lacks adequate context generalization; (b) It is unable to express complex context dependencies; (c) Parameters generated from this structure represent sudden transitions between adjacent states; (e) This... 

Diverse methods of producing semi-solid metal have been the subject of extensive study for the past 40 years. Among all these methods, electromagnetic stirring (EMS) and gas induced semi solid (GISS) have been used on a commercial scale. Considering the fact that in previous studies the intensity of electromagnetic field in the central part of the stirring chamber was negligible, a hollow cylinder with an almost pure iron core was utilized in the central part of the chamber in order to intensify the electromagnetic field in the center and to introduce gas bubbles into the melt. Aluminum A356 alloy was stirred by a three phase electromagnetic stirrer and introduction of gas bubbles under... 

This thesis is focused on the spoken term detection system based on speech recognition in low resources conditions. A spoken term detection system is composed of two parts: speech recognition and search. In search of words, the method of proxy words is used as a basic approache to overcome the problem of OOV words. The main challenge in this thesis in the context of low resources, is poor training acoustic and language models and the small lexicon in speech recognition. Small lexicon increases the number of OOV words. In this thesis, two innovation has been proposed to improve the basic system. The first is training a bottleneck neural network for extraction the articulatory features of... 

Iran's electrical grid is connected to the Eastern Turkey grid via Khoy-Basqale 400KV transmission line. Harmonic mesurements indicate high level of the 5th harmonic voltage in Azarbayjan grid which is magnified in Van substation. According to Iran international obligations and economic losses caused by the high level of harmonics in Azerbaijan regional electricity grid, a comprehensive study is required. Early studies showed that this unprecedented increase in the 5th harmonic voltage is due to the small harmonic loads scattered throughout the network. The aim of this thesis is to perform a comprehensive harmonic analysis of Azerbaijan network due to scattered harmonic loads. In this... 

A microgrid is a collection of loads, sources, and power storage units that operates as a single controllable system and can operate in grid-connected or islanded mode. From the generating side, renewable energy resources such as photovoltaic system, fuel cell and power storage units are inherently DC. From the load side, electronic loads such as computers, data centers and most of the variable speed motor drives require a DC supply. Therefore, DC Microgrids have gained widespread attention in recent years. On the other hand, since existing distribution systems are mostly AC, a hybrid microgrid is more likely. The hybrid microgrid is composed of two AC and DC subgrids interlinked by power... 

Music information reterival systems have a lot of applications in music filtering and broadcast monitoring due to the huge amount of multimedia data these days. In these systems the feature extraction method is called audio fingerprinting. Small size of fingerprints allows the systems to search efficiently in thousands or millions numbers of audio songs. The input signal is usually just a couple of seconds long and degraded in several ways. The goal is to design a system which is robust to signal degradations and efficient to search. In this thesis one of the basic systems is reviewed and improved in several ways. This system uses spectrogram of signals to extract features and build an...