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edalatzadeh--mohammad-sajjad
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Boundary exponential stabilization of non-classical micro/nano beams subjected to nonlinear distributed forces
, Article Applied Mathematical Modelling ; Volume 40, Issue 3 , 2016 , Pages 2223-2241 ; 0307904X (ISSN) ; Alasty, A ; Sharif University of Technology
Elsevier Inc
2016
Abstract
In this paper, the vibration suppression of micro- or nano-scale cantilever beams used in M/NEMS devices is studied. The beam is subjected to some nonlinear distributed forces, namely electrostatics force with first order fringing field correction, Casimir, and van der Waals forces. For the sake of precision, the beam is modeled by strain gradient elasticity theory capable of predicting the size effects in mechanical behavior of small-scale flexible structures. Since the governing partial differential equation of motion is nonlinear, the linearization approach is adopted to tackle the control problem. A novel control law is proposed that guarantees the exponential stability of the linearized...
Observer Based Stabilization of Partial Differential Equations Governing Strain Gradient Micro Beams
, M.Sc. Thesis Sharif University of Technology ; Alasti, Aria (Supervisor) ; Fotouhi Firouzabad, Morteza (Co-Advisor)
Abstract
In recent decades, the study of Nano and Micro Electromechanical Systems (NEMS and MEMS) as in micro sensors and actuators or in Atomic Force Microscopes (AFM) attracted considerable attention. Since an indispensable part of such systems is a nano or micro flexible beam, the inevitable undesirable vibrations of the flexible beam necessitate the implementation of vibration control strategies. Recently, some cutting edge experiments on statics and dynamics behavior of micro beams have been conducted that reveal some deviations from the prediction of classical theories, and hence this leads to development of strain gradient elasticity theory. In addition, the often-adopted finite dimensional...
Suppression of dynamic pull-in instability in electrostatically actuated strain gradient beams
, Article 2014 2nd RSI/ISM International Conference on Robotics and Mechatronics, ICRoM 2014 ; 2014 , pp. 155-160 ; ISBN: 9781479967438 ; Vatankhah, R ; Alasty, A ; Sharif University of Technology
2014
Abstract
In this paper, vibration suppression of micro-or nano-scale beams subjected to nonlinear distributed electrostatic force is studied. For the sake of precision, we use the beam model derived from strain gradient elasticity theory aimed at prediction of size effect. In addition, the electrostatic force is considered with first order fringing field correction. The continuous model of the strain gradient beam is truncated by using Kantorovich method as a semi-analytical finite element method. A boundary control feedback law is proposed to suppress forced vibrations of the beam. Both measurements and actuations are taken place in the boundary to avoid spillover instabilities. Simulation results...
Experimental Investigation of Fretting Fatigue of Titanium Specimens Made by Additive Manufacturing Method
, M.Sc. Thesis Sharif University of Technology ; Adibnazari, Saeed (Supervisor)
Abstract
Additive manufacturing (AM) has gained significant attention in recent years as a novel approach to fabricate three-dimensional parts. Its advantages, including high speed, low-cost production for small-scale batches, and greater design freedom, have made it a competitive alternative to traditional manufacturing methods. However, the application of AM for components subjected to fretting fatigue requires careful evaluation. Fretting fatigue is a major cause of failure in turbines, particularly at the contact interface between turbine blade roots and disk. In this study, the influence of AM and post-processing treatments on the fretting fatigue life of Ti-6Al-4V alloy was investigated. Five...
Analytical Investigation and Evaluation of Vulnerability of Deep Networks to Adversarial Perturbations
, M.Sc. Thesis Sharif University of Technology ; Ghaemmaghami, Shahrokh (Supervisor) ; Amini, Sajjad (Co-Supervisor)
Abstract
One of the most important problems in machine learning is investigating the performance of the learning algorithms, and especially deep neural networks, on adversarial examples, which are generated by imperceptibly perturbing input images, so that cause the model make a wrong prediction. Not only this line of research is important for making deep neural networks dependable, but also can help with understanding the fundamental limitations of deep neural networks, and the nature of their operation, which can in turn provide researchers with valuable insights into artificial intelligence. In this research work, we have tried to approach the topic with a mainly theoretical mindset. The method we...
Face Forgery Detection Through Statistical Analysis and Local Correlation Investigation
, M.Sc. Thesis Sharif University of Technology ; Ghaemmaghami, Shahrokh (Supervisor) ; Amini, Sajjad (Supervisor)
Abstract
Existing face forgery detection methods mainly focus on certain features of images, such as features related to image noise, local textures or frequency statistics of images for forgery detection. This makes the extracted representations and the final decision depend on the data in the database and makes it difficult to detect forgery with unknown manipulation methods. Solving this challenge, which is called the generalization challenge in artificial intelligence literature, has become the main goal of researchers in this field. In this thesis, the focus is on extracting effective features for success in forgery detection and preventing the performance of the forgery detection network from...
Robustification of Deep Learning Structures Based Ongenerative Models
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Reza (Supervisor) ; Amini, Sajjad (Supervisor)
Abstract
In recent years, deep learning has experienced rapid and remarkable advancements, demonstrating exceptional performance in various applications such as computer vision, natural language processing, and autonomous vehicles. These models are continually evolving and expanding, yet they harbor inherent vulnerabilities that prevent complete trust in their reliability. One of the most critical issues is their susceptibility to adversarial attacks, where a clean image is subtly manipulated to create an adversarial example. Adversarial examples, generated by adding imperceptible perturbations to input data, can easily mislead deep learning models into making highly confident yet incorrect...
Analysis and Enhancement of Low Voltage Ride Through Of Wind Turbines with Brushless Doubly Fed Induction Generator
, Ph.D. Dissertation Sharif University of Technology ; Oraee Mirzamani, Hashem (Supervisor) ; Tohidi, Sajjad (Co-Advisor)
Abstract
Wind energy technologies guarantee low pollution and operational costs. Using a DFIG and a fractionally rated power electronics converter gives variable speed operation with a low cost drive train. As energy policy organizations have allocated a considerable quota of wind energy generation to offshore wind farms, the absence of slip rings and brushes in the brushless DFIG (BDFIG) is an advantage for offshore wind turbines where maintenance is vital and expensive. With increasing wind power penetration in power systems, grid code requirements are an important consideration for the ride-through capability of wind farms through voltage dips, particularly for multi- MW wind turbine generators....
Optical bistability in fiber ring resonator containing an erbium doped fiber amplifier and quantum dot doped fiber saturable absorber
, Article Applied Optics ; Volume 51, Issue 29 , 2012 , Pages 7016-7024 ; 1559128X (ISSN) ; Farshemi, S. S ; Sajjad, B ; Shahshahani, F ; Bahrampour, A. R ; Sharif University of Technology
2012
Abstract
In this paper we study the optical bistability in a double coupler fiber ring resonator which consists of an erbium doped fiber amplifier (EDFA) in half part of the fiber ring and a quantum dot doped fiber (QDF) saturable absorber in the other half. The bistability is provided by the QDF section of the ring resonator. The EDFA is employed to reduce the switching power. The transmitted and reflected bistability characteristics are investigated. It is shown that the switching power for this new bistable device is less than 10 mW
Modeling and analysis of the dynamic response of an off-grid synchronous generator driven micro hydro power system
, Article International Journal of Renewable Energy Development ; Volume 10, Issue 2 , 2021 , Pages 373-384 ; 22524940 (ISSN) ; Farooq, H ; Rasool, A ; Sajjad, I. A ; Zhenhua, C ; Ning, L ; Sharif University of Technology
Diponegoro university Indonesia - Center of Biomass and Renewable Energy (CBIORE)
2021
Abstract
This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed...
Modeling and analysis of the dynamic response of an off-grid synchronous generator driven micro hydro power system
, Article International Journal of Renewable Energy Development ; Volume 10, Issue 2 , 2021 , Pages 373-384 ; 22524940 (ISSN) ; Farooq, H ; Rasool, A ; Sajjad, I. A ; Zhenhua, C ; Ning, L ; Sharif University of Technology
Diponegoro university Indonesia - Center of Biomass and Renewable Energy (CBIORE)
2021
Abstract
This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed...
Compact 5G millimeter-wave dual-band filter with application in filtenna
, Article Microwave and Optical Technology Letters ; Volume 63, Issue 2 , 2021 , Pages 620-625 ; 08952477 (ISSN) ; Jafarieh, A ; Behroozi, H ; Mallat, N. K ; Jamaluddin, M. H ; Sajjad Abazari, S ; Sharif University of Technology
John Wiley and Sons Inc
2021
Abstract
In this article, a dual-band sixth order double symmetric T-slot filter is proposed for the 5G communication systems. This filter contains two duplicate square resonators and a T-shape feedline on the Rogers RT duroid 5880 substrate. Operating at the 28 and 38.5 GHz frequencies from licensed 5G frequency bands and small size make this filter appropriate for different 5G applications. Furthermore, an LC equivalent circuit for the filter has been considered that helps us to have a better sight of this filter. Measurement results show good agreement with simulations. The attenuation on the passband is less than 1 dB. In order to evaluate the filter performance besides other millimeter waves...
Improving Robustness of Deep Networks to Adversarial Perturbations based on Ensemble Structure
, M.Sc. Thesis Sharif University of Technology ; Ghaemmaghami, Shahrokh (Supervisor) ; Marvasti, Farokh (Supervisor) ; Amini, Sajjad (Co-Supervisor)
Abstract
Deep learning is one of the most powerful branches of machine learning, demonstrating exceptional performance in tasks such as image and speech recognition with the help of neural networks. However, deep learning networks are highly vulnerable to small and intentional changes in input data, known as adversarial perturbations. These perturbations, despite having a significant impact on the model's output, are usually imperceptible to humans and can pose serious security challenges in sensitive areas such as autonomous vehicles and medical diagnostics. To counter these perturbations, extensive research has been conducted, most of which has utilized a single deep learning network to create a...
Construction of an Experimental Device for Foaming Agent and an Experimental Study of the Properties of Foaming Agent
, M.Sc. Thesis Sharif University of Technology ; Bazargan, Mohammad (Supervisor)
Abstract
The primary purpose of acidizing operations in the oil and gas industry is to enhance hydrocarbon production. Acidizing has been a common and conventional method for years, especially when production engineers face issues like declining reservoir pressure leading to reduced production rates. Initially, the treatment solution is referred to as matrix acidizing. In acidizing operations, different additives are combined with the acid to control its behavior in the reservoir. These additives may include iron control agents, corrosion inhibitors, friction reducers, and more. Incompatibility among these additives, the acid, and reservoir fluids can lead to severe damage to the reservoir....
Numerical Analysis of An Annular Gas Turbine Combustor
, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad (Supervisor)
Abstract
The goal of this research is the simulation of the annular combustion chamber of the turbine engine utilized by liquid fuel. The achievement to this goal will lead to create numerical tools for parametric study, analysis and combustion chamber designing.For this reason simple geometry has been considered. This simplicity of geometry causes to facilitate in parametric study and decrease in saving time for modeling and meshing. This combustion chamber is a simplified model of engine CF6. In recent study, the k – ε realizable model has been used for turbulence modeling. For non-adiabatic condition, chemical reaction is dissolved by utilizing probability density function along with laminar...
A misbehavior‐tolerant multipath routing protocol for wireless Ad hoc networks [electronic resource]
, Article International Journal of Research in Wireless Systems (IJRWS) ; Vol. 2, Issue 9, pp. , Sep. 2013 ; Pakravan, Mohammad Reza ; Aref, Mohammad Reza ; Sharif University of Technology
Abstract
Secure routing is a major key to service maintenance in ad hoc networks. Ad hoc nature exposes the network to several types of node misbehavior or attacks. As a result of the resource limitations in such networks nodes may have a tendency to behave selfishly. Selfish behavior can have drastic impacts on network performance. We have proposed a Misbehavior-Tolerant Multipath Routing protocol (MTMR) which detects and punishes all types of misbehavior such as selfish behavior, wormhole, sinkhole and grey-hole attacks. The protocol utilizes a proactive approach to enforce cooperation. In addition, it uses a novel data redirection method to mitigate the impact of node misbehavior on network...
Theoretical and Experimental Study to Conversion of AUC to UO2 by Microwave Heating
, Ph.D. Dissertation Sharif University of Technology ; Otukesh, Mohammad (Supervisor) ; Ghannadi Maragheh, Mohammad (Co-Advisor) ; Ghasemi, Mohammad Reza (Co-Advisor)SAR Imaging Using the TomoSAR Technique to Resolve Multiple Scatterers
, M.Sc. Thesis Sharif University of Technology ; Bastani, Mohammad Hassan (Supervisor) ; Karbasi, Mohammad (Co-Supervisor)
Abstract
During the last few years, the study of urban environment structures is considered as a research field of interest in remote sensing. In satellite observations of the earth's surface, continuous imaging in terms of time and space has caused the remote sensing technique to be proposed as a useful and efficient tool for the analysis of urban areas. Obtaining quantitative spatial information from the urban environment in fields such as determining the height of buildings plays an essential role in urban planning, monitoring damage to buildings, establishing communication bases and digital cities. During the last two decades, the use of Tomosar approach in order to reconstruct the structures of...
Estimating Possible Effects of Subsidies in Competition and Development of Fixed Broadband Internet
, M.Sc. Thesis Sharif University of Technology ; Vesal, Mohammad (Supervisor) ; Rahmati, Mohammad Hossein (Supervisor)
Abstract
In this work, the dynamic competition between firms providing internet services is studied. The framework is Markov equilibrium whereby structural parameters are obtained using two-step estimations, allowing for analyzing the situation in case of subsidies for service upgrade. The results show that such subsidy has little effect on the number of firms while increasing the number of fast firms
Estimating Price Elasticity of Natural Gas Demand in Iran's Residential Sector: A Regression Discontinuity Approach
, M.Sc. Thesis Sharif University of Technology ; Rahmati, Mohammad Hossein (Supervisor) ; Vesal, Mohammad (Supervisor)
Abstract
Estimating the price elasticity of gas demand involves complexities depending on the gas market structure and pricing mechanisms in different countries. Distinguishing between supply and demand shocks and block pricing are among the main challenges that can cause endogeneity in elasticity estimates. Iran's domestic gas network, one of the largest and most extensive household gas markets, is divided into five climatic zones based on weather conditions. The pricing steps for these five climates during the five cold months are such that a customer in a warmer climate pays higher prices. Conversely, the pricing steps for the seven warm months are the same for all climates. This policy creates a...