Sharif Digital Repository

This research concentrates on active and passive control of vibrations from a dieselgenerator set. A comprehensive study of the system is performed to design a system to provide minimum vibration transmission from a mid size generator set (300 kw) in a wide frequency range around operating point. The control system consists of two stages, a passive part with mode separation feature and an active part inserting control force by inertial actuators on the intermediate mass. Independence of the performances of passive and active parts of control system and low energy consumption of the active system can be considered as the main advantaged of this system. To evaluate the controller design, a DOF... 

One of the important concepts in cosmology is that all of the observations is done on the past light-cone. In general, cosmological linear perturbation theory is done in a particular gauge and often on spacelike hyperplanes. Then in order to link quantities calculated in perturbation theory with observables, we have to take into account effects coming from projecting these quantities onto past light-cone. We aim in this thesis to study these effects and to calculate corrections over observable quantities such as, two point correlation function and power spectrum of matter perturbations in cosmos. For a particular observational example, in the end we study clustering of structures in... 

Let G be a graph with adjacency matrix A and Δ be a diagonal matrix whose diagonal entries are the degree sequence of G. Then the matrices L = Δ− A and Q = Δ+A are called Laplacian matrix and signless Laplacian matrix of G, respectively. The eigenvalues of A, L, and Q are arranged decreasingly and denoted by λ1 ≥ · · · ≥ λn, μ1 ≥ · · · ≥ μn ≥ 0, and q1 ≥ · · · ≥ qn ≥ 0, respectively. The energy of a graph G is defined as E(G) :=
n
i=1
|λi|.
Furthermore, the incidence energy, the signed incidence energy, and the H¨uckel energy of G are
defined as
IE(G) :=
n
i=1
√
qi, LE(G) :=
n
i=1
√
μi, HE(G) :=

2
r
i=1 λi, n=... 

Scale formation is an unpleasant phenomenon that occurs when the mixed fluids are incompatible. The scales damage the reservoir, wellbore and the surface facilities. They reduce the effective fluid path and increase the pressure drop of the system; so it is necessary to study the precipitation thermodynamics of scale formation, and present a trustable method for banning the scales from precipitation. In this project, it has been tried to study the value of precipitated scale due to the mixing of two incompatible waters (Civand and Sea Water). The results of which are compared with the results of a geochemical software named PHREEQC. Then, the performance of hydro chloridric acid as a scale... 

A traffic classifier maps each input stream into a pre-defined traffic class. If the traffic is encrypted using a protocol, such as SSL, or is protected using an encrypted tunnel, it's content would be hidden from the classifier, in which case the common traffic classification methods will be ineffective. Although common security mechanisms which provide information confidentiality to user can't hide all properties of messages, including length and time. Some of the newly presented methods of traffic classification utilize these properties and can actually classify messages without accessing their content. We will study such methods and their limitations in this thesis. Of all the encrypted... 

Drilling Operations constitute more than fifty percent of total costs of well construction operations. Due to this fact, optimization of drilling operations could have significant effect on decrease in total costs of well construction. It is mentioning worthy that there are a variety of parameters which affect drilling operations from the view point of optimization. In many cases several of those aforementioned parameters are contrary in nature. Thus obtaining an integrated approach to optimize the operation by considering these effects is necessity. The goal of this thesis is to investigate different influential parameters of drilling operation optimization and to develop computer-based... 

We report on numerical and intelligent modeling of three-dimensional laminar flow of non-Newtonian fluids driven by axial pressure gradient in annular media consisting of a coaxially rotating inner cylinder. This is an example of a rotating Couette flow with vast applications in food, oil and gas, and chemical engineering industries. We study the dynamics of pressure in and the velocities (in three directions X, Y and Z) of every grid in presence of rotation and without that by means of CFD. Afterward, we develop a novel predictive model based on an Artificial Neural Network (ANN). The hybrid ANN framework is trained and tested by over 100000 data which collected by CFD. We then perform... 

In this dissertation, we introduced a Fuzzy based representation and comparison method for sequential patterns such as speech and online handwriting. The new model, called Fuzzy Elastic Matching Machine (FEMM), is simpler than traditional HMM based approaches and is not based on the common statistical assumptions of HMM systems. The model was tested on isolated word and phoneme recognition tasks in speech recognition domain and isolated letter recognition in Persian handwriting recognition. We showed that this method is faster than traditional HMM based models and more robust to noise. To train the model, we introduced a Symbiogenesis-based evolutionary training algorithm. This algorithm... 

In recent years, unmanned vehicles have intensively been developed to reduce human dangers for marine applications. Predicting the hydrodynamic coefficients of an autonomous underwater vehicle is important during the vehicle’s design phase. In other words to design an AUV, one must clarify its maneuverability and controllability based on a mathematical model. The mathematical model contains various hydrodynamic forces and moments expressed collectively in terms of hydrodynamic coefficients. Therefore, the correct values of the coefficients must be known to precisely design the controller of AUVs.SUT-2 is an AUV, being developed by Marine Engineering Laboratory of Sharif University of... 

In this thesis failure analysis of a critical part in a landing gear of a commercial aircraft was conducted.Fatigue phenomenon was determined as the reason for the failure and fracture of the mentionedcomponent. Fractography investigation of the fracture surface and charasteristicswas conducted.Scanning Electron Microscope was utilized for the study of the fracture surface. In the fracture surface, fatigue striations were observed. An experimental model of the crack growth is presented by using the fracture surface characteristics. By counting the fatigue striations and measuring their distance betwwn them on the fracture surface, the rate of the crack growth and crack growth life were... 

Nowadays, the use of finite element Software applications in enigineering departments has become Inevitable and commonplace. Acceptance of the necessity of using such software applications for reducing the cost of research and development does not require any evidences of financial instruments to be presented. Reducing design and manufacture time together with pseudo-empirical approach has cuased the finite element science to become a conventional designing tools.
Since contact is the main method to apply a load on a ductile object,and stress concentration caused thereby is often a major cause of failure in mechanical parts, the issue of contact is a fundamental topic in mechanics of... 

In this project, the structure of an aircraft and its sensitive areas has been studied for fatigue damages and then the design philosophies have been analyzed. Subsequently, relevant analysis and calculations have been conducted on a critically important part of the airframe (due to its location), which has suffered fatigue due to the age of the aircraft. This part belongs to the airframe of a Boeing 747, known as frame 360 in section 41 of the body of the aircraft, in which the numerous flight cycles have led to the creation and propagation of fatigue crack.
In the first stage of this project, the remaining life time of the frame has been estimated using theoretical relationships. In... 

Most of the current application and potential FGM included in the areas related to contact mechanic .These issues essentially are related to the transfer of force between two objects, that in general is with friction, so in this study the contact under the loading of horizontal and vertical with its different aspect such as the effect of contact region, the effect of round and also the effect of getting harden and soften of FGM.
The used method is a numerical method ¬(finite element method) that will resulted in contact equation discretisce by use of Penalty method. In this thesis is also presented the needed algorithms for solving the problem and the finite element code for solving the... 

The reliability of integrated circuits (IC) is related to material imperfections such as holes, cavities, cracks and etc. which occur in the manufacturing process. The operational conditions of IC create thermal stresses. These thermal stresses increase the chance of failure by making the imperfections critical in IC’s components such as VIA that is used as connection between interconnects in the multilevel integrated circuits. As a result, thermal fatigue needs to be investigated in VIA thoroughly.
The thermal stresses in VIA increase the possibility of hole forming due to hydrostatic stresses during manufacturing process and the amplitude of applied stresses under the operational... 

In this study numerical methods are used for modeling flow and simulation of aerosol transport and deposition in alveolar zone of human lung. The flow modeling is done by FLUENT code, using its moving boundaries feature. For particle tracking we developed a code that uses results of velocity field obtained by FLUENT code. Two-dimensional the axisymmetric model was investigated in this study, and was exhibited that rhythmically expanding walls in alveolar duct model has significant influence on flow patterns and particles transport mechanism. In this study we also developed a three-dimensional model of a single alveolated duct with moving boundaries allowing for the cyclic expansion and... 

Wireless Sensor Networks (WSNs) are rapidly emerging as an important area in mobile computing research. Applications of WSNs are numerous and growing, some of them are even highly critical, like military or safety applications. Security measures must be applied to protect the network from a variety of attacks. Since no intrusion prevention measure is perfect, intrusion detection becomes an important second wall to protect the network. WSNs have unique nature which is different from other kinds of networks. In this project, we examine the characteristics and vulnerabilities of WSNs and propose a new intrusion detection model to protect the network security. In this work we have not only... 

There are lots of researches performed to investigate human being learning and try to model it. But, in case of huge complexity of its structure and function, almost none of so-far learning algorithms can model human learning process and, indeed, performance of human brain in real problems is much more than these algorithms. Moreover, in many cases, human is not aware or informed about internal structure or mathematical model of the present system he is working on; a child learning to walk has no information about his neuromuscular system and his brain slowly learns how to convey his little body by choosing the proper timing of muscle contractions. One of the accomplished researches in order... 

To achieve the highest amount of FOPT during reservoir life and the most net present value, the parameters that are effective in the production of the field are adjusted to be the best performance. In order to achieve these conditions, the reservoir model and the surface will be checked integrated so that the optimal mode of each parameter is determined in interaction with other parameters, so the first integrated model of the reservoir and the surface and then optimizing the target functions of cumulative production and the net present value is performed using the genetic algorithm.Since the number of parameters of reservoir model and surface in the studied field in this study is high,... 

Tinnitus is commonly referred to the symptom of “ringing in the ear”, and it is scientifically described as the perception of sound in the absence of an acoustic event. This symptom is powerful enough to negatively affect sleep patterns and concentration. The symptoms affect more than forty-five million people only in the US and 10 to 20% of the world population. Management and treatment of subjective tinnitus is an ongoing focus of research activities. Ample evidence suggests that the mechanism of tinnitus involves maladaptive plasticity in both classic and non-classic auditory pathway. The non-classical pathway is referred to multi-modal sensory inputs to the auditory system, limbic... 

In this work, we want to gain and analyze the dynamic equations of an open four bar mechanism with two flexible links and three flexible hinges. In continue, one of the applications of a 3-RRR mechanism has been mentioned and dynamic equations and angles behavior have been analyzed. The effect of hinge stiffnesses and their sequence has been investigated by using Hamilton principle. In addition, The behavior of the mechanism with flexible links has compared to the mechanism with non-flexible. At last, the results have been validated by ADAMS software.