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ramezani--mahdi
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Some Innovations in Numerical Simulation of Inviscid Three Dimensional Flow with Moving Boundaries
, Ph.D. Dissertation Sharif University of Technology ; Mazaheri, Karim (Supervisor)
Abstract
The main subject of this thesis is to improve conventional CFD algorithms applied in numerical simulation of inviscid unsteady flows around moving boundaries with large relative motions, on unstructured grids. All challenges in this regard are reviewed, and appropriate efficient schemes are introduced to address them. A new scheme is presented for valid grid generation during grid movement and is implemented for 2D and 3D problems. Customary three dimensional convergence acceleration techniques such as implicit time stepping and multigriding have been applied. For implicit solution of the flow equations a new algorithm is used. Via a special renumbering algorithm, the approximate...
Management of Storage Resources, Power, and Performance in Enterprise Storage Systems Using Prefetching Method
, M.Sc. Thesis Sharif University of Technology ; Asadi, Hossein (Supervisor)
Abstract
Nowadays, enterprise storage systems are widely used in data centers such as databases, servers, and bank institutes. Due to mechanical activity of disk drives, these systems are one of the most power consumptive components in data centers. Prefetching and RAID, which are employed to enhance performance, are widely used in data storage systems. These two methods, however, impose significant energy overhead to the system due to the increased disk activity. In this thesis, we first elaborate shortcomings of prefetching and RAID methods. Then, we propose a new energy efficient and RAID-compatible prefetching method (LPTAP), which aims at improving performance and energy consumption. To evaluate...
New Approaches to the Second Law of Thermodynamics and the Principle of Entropy Increasing
, M.Sc. Thesis Sharif University of Technology ; Golshani, Mehdi (Supervisor)
Abstract
In this dissertation we study the derivation of the second law of thermodynamics from an underlying physics. After discussing different methods for this derivation, we conclude that the only way to fulfill this, is to use a probabilistic mechanics which has probability as an inherent concept in itself, not as a supplementary one like statistical mechanics. This mechanics in contrary to the Newtonian mechanics, should be indeterministic
Analysis of Sight Distance in Railroad-Highway Grade Crossings in Iran
, M.Sc. Thesis Sharif University of Technology ; Vaziri, Manouchehr (Supervisor)
Abstract
In railway transportation network, there are spots that we have to intersect with highway network. These intersections break into two branches named grade crossing and unlevel crossing depend on their structure. Grade crossings from the view of protection are grouped into protected crossings and unprotected crossings. Protected crossings depend on their traffic control devices are categorized into active crossings and passive crossings.There are many factors that influence highway-railroad grade crossing design. Some of these factors can vary widely by drivers' behavior. These factors have been developed in models by AASHTO and its publications and shaped like we have them today. In order to...
Micropolar hypo-elasticity
, Article Archive of Applied Mechanics ; Volume 80, Issue 12 , December , 2010 , Pages 1449-1461 ; 09391533 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2010
Abstract
In this paper, the concept of hypo-elasticity is generalized to the micropolar continuum theory, and the general forms of the constitutive equations of the micropolar hypo-elastic materials are presented. A new co-rotational objective rate whose spin is the micropolar gyration tensor is introduced which describes the deformation of the material in view of an observer attached to the micro-structure. As special case, simplified versions of the proposed constitutive equations are given in which the same fourth-order elasticity tensors are used as in the micropolar linear elasticity. A 2-D finite element formulation for large elastic deformation of micropolar hypo-elastic media based on the...
Combined action of Casimir and electrostatic forces on nanocantilever arrays
, Article Acta Mechanica ; Volume 212, Issue 3-4 , July , 2010 , Pages 305-317 ; 00015970 (ISSN) ; Alasty, A ; Sharif University of Technology
2010
Abstract
Cantilever arrays with nearest-neighbor interactions are considered to obtain the pull-in parameters. The interactions between the neighboring beams are a combination of the Casimir force and the electrostatic force with the first-order fringing field correction. A set of coupled nonlinear boundary value problems and a set of coupled nonlinear equations arise in the distributed and lumped parameter modeling of the array, respectively. The models are simulated numerically to obtain the pull-in parameters of the arrays with different number of beams. The pull-in parameters of large arrays converge to constant values, which are independent of the number of beams in the array. The constants...
Comparison of supervised classification methods with various data preprocessing procedures for activation detection in fMRI data
, Article Springer Optimization and Its Applications ; Volume 38 , 2010 , Pages 75-83 ; 19316828 (ISSN) ; Fatemizadeh, E ; Sharif University of Technology
2010
Abstract
In this study we compare five classification methods for detecting activation in fMRI data: Fisher linear discriminant, support vector machine, Gaussian nave Bayes, correlation analysis and k-nearest neighbor classifier. In order to enhance classifiers performance a variety of data preprocessing steps were employed. The results show that although kNN and linear SVM can classify active and nonactive voxels with less than 1.2% error, careful preprocessing of the data, including dimensionality reduction, outlier elimination, and denoising are important factors in overall classification
Towards genetic feature selection in image steganalysis
, Article 2010 7th IEEE Consumer Communications and Networking Conference, CCNC 2010, 9 January 2010 through 12 January 2010, Las Vegas, NV ; 2010 ; 9781424451760 (ISBN) ; Ghaemmaghami, S ; Sharif University of Technology
2010
Abstract
In this study, a new feature-based steganalytic method is presented and four classification methods: Fisher Linear Discriminant, Gaussian naïve Bayes, Multilayer perceptron, and k nearest neighbor, are compared for steganalysis of suspicious images. The method exploits statistics of the histogram, wavelet statistics, amplitudes of local extrema from the 1D and 2D adjacency histograms, center of mass of the histogram characteristic function and co-occurrence matrices for feature extraction process. In order to reduce the proposed features dimension and select the best subset, genetic algorithm is used and the results are compared through principle component analysis and linear discriminant...
Adaptive image steganography with mod-4 embedding using image contrast
, Article 2010 7th IEEE Consumer Communications and Networking Conference, CCNC 2010, 9 January 2010 through 12 January 2010, Las Vegas, NV ; 2010 ; 9781424451760 (ISBN) ; Ghaemmaghami, S ; Sharif University of Technology
2010
Abstract
A new adaptive steganography method based on image contrast to improve the embedding capacity and imperceptibility of the stego images is presented. The method exploits the average difference between the gray level values of the pixels in 2x2 blocks of non-overlapping spatially and their mean gray level in order to select valid blocks for embedding. The method was tested on different gray scale images. Results show that our proposed approach provides larger embedding capacity, while being less detectable by steganalysis methods such as χ2 attack and machine learning steganalysis systems, as compared to some well-known adaptive and non-adaptive steganography algorithms
Multigrid convergence acceleration for implicit and explicit solution of Euler equations on unstructured grids
, Article International Journal for Numerical Methods in Fluids ; Volume 62, Issue 9 , 2010 , Pages 994-1012 ; 02712091 (ISSN) ; Mazaheri, K ; Sharif University of Technology
2010
Abstract
The multigrid method is one of the most efficient techniques for convergence acceleration of iterative methods. In this method, a grid coarsening algorithm is required. Here, an agglomeration scheme is introduced, which is applicable in both cell-center and cell-vertex 2 and 3D discretizations. A new implicit formulation is presented, which results in better computation efficiency, when added to the multigrid scheme. A few simple procedures are also proposed and applied to provide even higher convergence acceleration. The Euler equations are solved on an unstructured grid around standard transonic configurations to validate the algorithm and to assess its superiority to conventional explicit...
Instability of nanocantilever arrays in electrostatic and van der waals interactions
, Article Journal of Physics D: Applied Physics ; Volume 42, Issue 22 , 2009 ; 00223727 (ISSN) ; Alasty, A ; Sharif University of Technology
2009
Abstract
The structural instability of an array of cantilevers, each of which interacts with two neighbouring beams through electrostatic and van der Waals forces, is studied. Distributed and lumped parameter modelling of the array result in a set of coupled nonlinear boundary value problems and a set of coupled nonlinear equations, respectively. These coupled nonlinear systems are solved numerically for different numbers of beams in the array to obtain the pull-in parameters. The pull-in parameters converge to constant values with an increase in the number of beams in the array. These constants, which are important in the design of cantilever arrays, are compared for the distributed and lumped...
Fault Tolerant Model Predictive Control of Tethered Satellite System
, M.Sc. Thesis Sharif University of Technology ; Asadian, Nima (Supervisor)
Abstract
In this thesis, a control method to cope with the fault in the two-satellite two-tether satellite systems has been proposed to avoid failing the mission in the case one tether is torn. A new model for the tethered satellite system with two tethers has been developed to show the effects of tethers’ tension forces in the attitude dynamics. One of the main features of this model is the ability of changing the tethers’ connection points to the co-satellite for attitude control purposes. As a result, tethers’ tension forces are used as control actions to reduce the fuel consumption. The introduced coupled tethered satellite system has been controlled using the model predictive control method....
Thermodynamical Investigation of Quantum Systems
, Ph.D. Dissertation Sharif University of Technology ; Golshani, Mehdi (Supervisor)
Abstract
Investigation of the consistency between physical theories has always resulted in the advancement of physics. Meanwhile, study of the consistency between quantum mechanics and thermodynamics has led to the development of a branch in theoretical physics called quantum thermodynamics. In addition to the consistency problem,employing other features of quantum mechanics such as coherency and entanglement, to enhance thermodynamic processes is another ongoing subject of research. In order to study the thermodynamics of quantum systems, we use the first law of thermodynamics to present a derivation of quantum potential. Quantum potential is a term in the equations of motion of a quantum system of...
Energy pairs in the micropolar continuum
, Article International Journal of Solids and Structures ; Volume 44, Issue 14-15 , 2007 , Pages 4810-4818 ; 00207683 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2007
Abstract
In this paper, the concept of energy pairs in the micropolar continuum is introduced. A brief review of the micropolar continuum theory is presented for using in the subsequent derivations. A mathematical Lagrangian strain and a wryness tensor for the micropolar continuum are introduced. Using the first law of thermodynamics and for isothermal processes, the power of deformation is obtained and the energy pairs in the Eulerian and Lagrangian descriptions are defined. Also, the micropolar stress and couple stress tensors which are energy pairs to the micropolar Lagrangian strain and wryness measures are determined. © 2006 Elsevier Ltd. All rights reserved
Nonlinear free vibrations of a Timoshenko beam using multiple scales method
, Article Proceedings of the 7th Biennial Conference on Engineering Systems Design and Analysis - 2004, Manchester, 19 July 2004 through 22 July 2004 ; Volume 2 , 2004 , Pages 101-106 ; 0791841731 (ISBN); 9780791841730 (ISBN) ; Ghorashi, M ; Sharif University of Technology
American Society of Mechanical Engineers
2004
Abstract
In this paper, the large amplitude free vibration of a cantilever Timoshenko beam is considered. To this end, first Hamilton's principle is used in deriving the partial differential equation of the beam response under the mentioned conditions. Then, implementing the Galerkin's method the partial differential equation is converted to an ordinary nonlinear differential equation. Finally, the method of multiple scales is used to determine a second order perturbation solution for the obtained ODE. The results show that nonlinearity acts in the direction of increasing the natural frequency of the thick-cantilevered beam
A Novel Approach to Mixed Model and Goal Coordination of Large-Scale Systems
, Ph.D. Dissertation Sharif University of Technology ; Sadati, Naser (Supervisor)
Abstract
In this thesis, a new approach is proposed for two-level optimal control of large-scale nonlinear systems. In this approach, by defining some parameters as coordination parameters the overall system is decomposed into several interactive subsystems, where the optimization problem redefines for each one of them. The obtained sub-problems which are in the form of standard optimal control problems with lower dimension are solved in the first level. To obtain the overall optimal solution, coordination of the first level solutions is performed in the second level. For solving the first level problems, the indirect gradient and Newton methods are used. The gradient method is applied in the first...
Interval Determination for Coefficients of a Characteristic Polynomial in Order to Restrict the Location of the Roots
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohammad (Supervisor)
Abstract
One of usual criterion which detrimines how much two polynomials are close to each other is smallness of the norm of vector that is formed from subtraction of their corresponding coefficients. Using this criterion, in this dissertation we become involved in investigation of two similar problems. First one is determination of the closest non-Hurwitz polynomial to a Hurwitz one. During this activity, the robustness margin of Hurwitz polynomial whose coefficients are subject to uncertainty is determined. The second problem is determination of the closest Hurwitz polynomial to another polynomial which is not Hurwitz. Unlike to the first problem, this problem is extremely hard. The solution of...
Turboexpander Technology Development Model and Display Roadmap for Pressure Reducing System based Energy Recovery by Turboexpander
, M.Sc. Thesis Sharif University of Technology ; Saboohi, Yadollah (Supervisor)
Abstract
High pressure natural gas is transported from processing plants to end users via a network of natural gas system. Pressure reduction along the transport system is compensated in compressor stations. High pressure natural gas flows in to distribution network in demand center which operates at medium pressure. Medium pressure gas is transferred to end users who can use natural gas with low pressure. Therefore, pressure of natural gas is reduced consequently when gas flows from transport systems to distribution network and end users. Work is dissipated during pressure reduction which otherwise could be converted in to power.A technology that could be utilized for conversion of pressure work in...
Overview of MAC protocols for energy harvesting wireless sensor networks
, Article IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 30 August 2015 through 2 September 2015 ; Volume 2015-December , 2015 , Pages 2032-2037 ; 9781467367820 (ISBN) ; Pakravan, M. R ; Sharif University of Technology
2015
Abstract
Wireless Sensor Networks (WSNs) have been weaved into the fabric of our daily lives. The foremost impediment in the rapid development of these networks is the energy limitation which inhibits them from meeting specific application requirements. Recently, the advances in energy harvesting technology have made it possible to replenish the energy of sensors via external sources. Energy Harvesting-Wireless Sensor Networks (EH-WSNs) are being transformed from a visionary concept into reality. However, this concept is still in its infancy and calls for extensive research to cater to the needs of WSNs. For future progress of EH-WSNs, Medium Access Control (MAC) layer has undoubtedly a decisive role...
Hierarchical optimal control of large-scale nonlinear chemical processes
, Article ISA Transactions ; Volume 48, Issue 1 , January , 2009 , Pages 38-47 ; 00190578 (ISSN) ; Sadati, N ; Sharif University of Technology
2009
Abstract
In this paper, a new approach is presented for optimal control of large-scale chemical processes. In this approach, the chemical process is decomposed into smaller sub-systems at the first level, and a coordinator at the second level, for which a two-level hierarchical control strategy is designed. For this purpose, each sub-system in the first level can be solved separately, by using any conventional optimization algorithm. In the second level, the solutions obtained from the first level are coordinated using a new gradient-type strategy, which is updated by the error of the coordination vector. The proposed algorithm is used to solve the optimal control problem of a complex nonlinear...