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An ABS Algorithm for Solving a System of Nonlinear Equations and Linear Inequalities with Application to Distillation Tower Design
, M.Sc. Thesis Sharif University of Technology ; Mahdavi Amiri, Nezamoddin (Supervisor)
3-Axis Attitude Control of a Satellite with Two Reaction Wheels Using Heuristic Algorithms
,
M.Sc. Thesis
Sharif University of Technology
;
Nejat Pishkenari, Hossein
(Supervisor)
;
Salarieh, Hassan
(Supervisor)
Abstract
In this study, the attitude control of an under-actuated satellite has been investigated. The investigated satellite uses reaction wheels for attitude control. For having full controllability of a satellite attitude, at least three reaction wheels are required. However, due to the high failure rate of reaction wheels, in this study assumed the satellite has two perpendicular reaction wheels, which causes the satellite to be under-actuated. The path planning method is used for controlling the satellite, which is an offline method. In the beginning, tries to define the control input of the satellite in term of limited parameters with different methods. In this regard, the control input is...
Optimal Trajectory Planning for Aircraft Microgravity Atmospheric Maneuver
, M.Sc. Thesis Sharif University of Technology ; Pourtakdoust, Hossein (Supervisor)
Abstract
The purpose of the current study is to design an optimal trajectory and control for an aircraft to perform a microgravity maneuver automatically. This subject is by itself an important research topic that has not yet been attempted via optimal control formulation and modelling. Space stations are commonly utilized to conduct long-term microgravity research. Unfortunately utility of space stations to perform space based microgravity experiments is expensive and inaccessible for many researchers and scientific institutions. However, since many experiments requiring microgravity conditions can be performed in short time intervals, there is a possibility to meet their demand via optimal...
Numerical modeling of pulse tube refrigerator and sensitivity analysis of simulation
, Article HVAC and R Research ; Volume 19, Issue 3 , 2013 , Pages 242-256 ; 10789669 (ISSN) ; Saidi, M. H ; Ghahremani, A. R ; Sharif University of Technology
2013
Abstract
In this article a double-inlet pulse-tube refrigerator (DIPTR) is modeled using the nodal analysis technique. The main complexity of the problem is oscillatory and unsteady characteristics of the flow. Solving the flow field in the regenerator section of the system as a porous medium with nonlocal thermal equilibrium is challenging. Governing equations are developed applying mass, energy, and momentum equations to different finite volumes in each component of DIPTR. A numerical code (SharifPTR), with graphical user interface, has been developed to investigate the influence of geometrical and working parameters on performance. The governing equations are a system of boundary value problems....
Modelling correlation between hot working parameters and flow stress of IN625 alloy using neural network
, Article Materials Science and Technology ; Volume 26, Issue 5 , Jul , 2010 , Pages 621-625 ; 02670836 (ISSN) ; Behjati, P ; Sharif University of Technology
2010
Abstract
In this work, an optimum multilayer perceptron neural network is developed to model the correlation between hot working parameters (temperature, strain rate and strain) and flow stress of IN625 alloy. Three variations of standard back propagation algorithm (Broyden, Fletcher, Goldfarb and Shanno quasi-Newton, Levenberg-Marquardt and Bayesian) are applied to train the model. The results show that, in this case, the best performance, minimum error and shortest converging time are achieved by the Levenberg-Marquardt training algorithm. Comparing the predicted values and the experimental values reveals that a well trained network is capable of accurately calculating the flow stress of the alloy...
New Approaches for Solving Fuzzy LR Linear Systems and a Class of Fuzzy Location Problems
, Ph.D. Dissertation Sharif University of Technology ; Mahdavi Amiri, Nezamoddin (Supervisor)
Abstract
By increasing complexity of systems, soft computing including fuzzy computing, evolutionary computing and intelligent computing, have been developing in recent years. Here, we focus on two subjects making use of soft computing. Firstly, we study fuzzy LR linear systems.
We transform the fuzzy linear system into a corresponding linear crisp system and a constrained least squares model. We show that the fuzzy LR system has an exact solution if and only if the corresponding crisp system is compatible (has a solution) and the optimal value of the corresponding least squares problem is equal to zero. In this case, the exact solution is determined by the solutions of the two corresponding...
We transform the fuzzy linear system into a corresponding linear crisp system and a constrained least squares model. We show that the fuzzy LR system has an exact solution if and only if the corresponding crisp system is compatible (has a solution) and the optimal value of the corresponding least squares problem is equal to zero. In this case, the exact solution is determined by the solutions of the two corresponding...
Investigation on the importance of the diffusion process during lean gas injection into a simple synthetic depleted naturally fractured gas condensate reservoir
, Article Petroleum Science and Technology ; Volume 30, Issue 7 , Feb , 2012 , Pages 655-671 ; 10916466 (ISSN) ; Gerami, S ; Ghotbi, C ; Hashemi, A ; Sharif University of Technology
2012
Abstract
A depleted naturally fractured gas condensate reservoir with extremely tight matrix permeability in the center of Iran is used for gas storage. Due to the tightness of the matrix, simulation of this process may present a unique challenge in terms of the importance of diffusion process in flow behavior of the injected gas in matrix blocks. This article presents a multimechanistic (Darcian-type flow and Fickian-type flow) mathematical model to investigate the importance of diffusion process as a function of important rock and fluid parameters. The authors' approach consists of the following steps: (a) development of a 1-D governing equations for a single matrix block consists of a gas...