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farmahini-farahani--a
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Maintenance Planning at Generation by GENCO & ISO in Restructured Power System
, M.Sc. Thesis Sharif University of Technology ; Ehsan , Mehdi (Supervisor)
Abstract
In a centralized power system, the system operator, derives a maintenance scheduling plan that maximizing reliability of system and minimizing operating cost. But in a restructured power system the goals of GENCOs and independent system operator (ISO) are separate and each of them optimize its own goal. The goal of each GENCO is to maximize its annual benefits and the goal of ISO is to maximize the reliability of system throughout the year. Therefore there are two objective functions for finding an optimum maintenance schedule in restructured power system. This thesis proposes a new method for maintenance scheduling of generation units in a restructured power system. Firstly each GENCO...
Developing an Agile Product Line Engineering Methodology
, M.Sc. Thesis Sharif University of Technology ; Ramsin, Raman (Supervisor)
Abstract
Software Product Line Engineering (PLE) and Agile Software Development are two leading approaches in the software industry. Despite the inherent differences between the two approaches, they are intended to fulfill common goals, such as: Reducing time to market, increasing customer satisfaction, promoting product quality, managing changes in requirements, and lowering the costs of development. In addition, each of them has certain positive features which address the other’s weaknesses. As a result, it seems reasonable to integrate the two approaches in order to produce a combined method which fulfills the common goals while addressing the weaknesses. Agile Product Line Engineering (APLE) is a...
Investigation of Effective Microstructural Parameters on the Stress Whitening in Polypropylene Blends
, Ph.D. Dissertation Sharif University of Technology ; Bagheri, Reza (Supervisor)
Abstract
Stress whitening is a type of discoloration that can occur in variety of polymers used in automotive and household industries. The current research tries to investigate the effective microstructural parameters such as strain rate, rubber second phase, and branched polypropylene (PP) on the stress whitening in polypropylene in order to propose toughed PP blends with limited stress whitening. It is shown that increasing the strain rate in tensile test results in formation of more visible whitened area within the plastically deformed zone. This is the consequence of further growth of micro-voids at higher strain rates. The results are in accordance with the Mie scattering concepts. Besides, the...
Graph Signal Prediction using Graph and Temporal Smoothing
,
M.Sc. Thesis
Sharif University of Technology
;
Babaiezadeh, Massoud
(Supervisor)
Abstract
The problem of linear prediction is one of the traditional issues in signal processing. With the genesis of graph signal processing, the prediction of signals defined on graphs has been recently addressed. Some existing methods provide approaches for predicting samples of a graph signal based on a known adjacency matrix among nodes. On the other hand, some studies have used graph smoothing technique, which ensures that the estimated signals remain smooth on the graph. Furthermore, graph neural networks have been proposed recently, and some research has considered methods for predicting graph signals using a graph neural network, which is possible by using extracted features from the training...
HW/SW partitioning using discrete particle swarm
, Article 17th Great Lakes Symposium on VLSI, GLSVLSI'07, Stresa-Lago Maggiore, 11 March 2007 through 13 March 2007 ; 2007 , Pages 359-364 ; 159593605X (ISBN); 9781595936059 (ISBN) ; Kamal, M ; Fakhraie, S. M ; Safari, S ; Sharif University of Technology
2007
Abstract
Hardware/Software partitioning is one of the most important issues of codesign of embedded systems, since the costs and delays of the final results of a design will strongly depend on partitioning. We present an algorithm based on Particle Swarm Optimization to perform the hardware/software partitioning of a given task graph for minimum cost subject to timing constraint. By novel evolving strategy, we enhance the efficiency and result's quality of our partitioning algorithm in an acceptable run-time. Also, we compare our results with those of Genetic Algorithm on different task graphs. Experimental results show the algorithm's effectiveness in achieving the optimal solution of the HW/SW...
Estimation of the initial blank shape and strain distribution for complicated geometries in sheet metal forming by a nonlinear inverse finite element method
, Article SAE Technical Papers ; 2012 ; Assempour, A ; Sharif University of Technology
SAE
2012
Abstract
A nonlinear inverse finite element method is developed for estimation of initial blank shape and strain distribution in final shape. This method often based on implicit static algorithms, causes sometimes convergence problems because of strong nonlinearities. In order to avoid the converging problems, especially in the quasi vertical walls, an appropriate initial guess is introduced. By using this initial guess, the number of iterations in the nonlinear numerical solution is decreased, solution speed is significantly increased and complicated geometries can be analyzed by this method with good accuracy. Application to a Srail part shows good agreement between commercially available finite...
Study of buzz phenomenon using visualization of external shock structure
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; 2018 ; 09544100 (ISSN) ; Jaberi, A ; Sharif University of Technology
SAGE Publications Ltd
2018
Abstract
An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and...
Study of buzz phenomenon using visualization of external shock structure
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 233, Issue 7 , 2019 , Pages 2690-2698 ; 09544100 (ISSN) ; Jaberi, A ; Sharif University of Technology
SAGE Publications Ltd
2019
Abstract
An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and...
Study of buzz phenomenon using visualization of external shock structure
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 233, Issue 7 , 2019 , Pages 2690-2698 ; 09544100 (ISSN) ; Jaberi, A ; Sharif University of Technology
SAGE Publications Ltd
2019
Abstract
An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and...
Applying elastic unfolding technique in nonlinear inverse finite element method for sheet forming modeling
, Article Advanced Materials Research, 8 July 2011 through 11 July 2011 ; Volume 341-342 , July , 2012 , Pages 242-246 ; 10226680 (ISSN) ; 9783037852521 (ISBN) ; Assempour, A ; Sharif University of Technology
2012
Abstract
A simplified efficient finite element method called the inverse approach (IA) has been developed to estimate initial blank and strain distribution in sheet metal forming. This algorithm is an inverse method since the position of points in final shape is known and their corresponding position in the initial blank should be determined. This approach deals with the geometric compatibility of finite elements, plastic deformation theory, and virtual work principle. This method often based on implicit static algorithms, sometimes causes convergence problems because of strong nonlinearities. This paper introduces an initial guess to speed up the convergence of Newton- Raphson solution. The...
A general methodology for bearing design in non-symmetric T-shaped sections in extrusion process
, Article Journal of Materials Processing Technology ; Volume 212, Issue 1 , 2012 , Pages 249-261 ; 09240136 (ISSN) ; Assempour, A ; Farahani, S ; Sharif University of Technology
2012
Abstract
In this study, a general methodology has been developed to design the proper bearing in order to eliminate the curvature of the final product in extrusion process. Three smooth curved (advanced-surface) dies with non-symmetric T-shaped sections and different off-centricities have been studied. For each die, the proper bearing has been designed and physical and numerical modeling have been performed to validate the design. The design procedure is as follows: A formulation, based on Bezier curves, has been used to determine the exit velocity profile. Since the result of Bezier method is different from the actual velocity profile, the Chitkara corrective function has been modified and applied...
United elements method for general contact-impact problems
, Article Computer Methods in Applied Mechanics and Engineering ; Volume 191, Issue 8-10 , 2001 , Pages 843-860 ; 00457825 (ISSN) ; Mofid, M ; Vafai, A ; Sharif University of Technology
2001
Abstract
This work presents the details of a finite element-based numerical method to analyse general contact/impact problems, called united elements method (UEM). In contrast to usual methods, that is Lagrange Multipliers and Penalty Function, this method is conceptual, suitable for computer programming, and free from inherent deficiencies of those methods. The key points of this procedure are elimination of the normal degree of freedom of the contactor node from the system energy potential functional in terms of target surface motion, and proper calculation of target element unbalanced forces, to incorporate the contact constraints. After a review on classic formulations, the mathematical and...
Design and analysis of a cooling system for a supersonic exhaust diffuser
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 233, Issue 14 , 2019 , Pages 5253-5263 ; 09544100 (ISSN) ; Fouladi, N ; Mirbabaei, A. R ; Sharif University of Technology
SAGE Publications Ltd
2019
Abstract
High-altitude test facilities are usually used to evaluate the performance of space mission engines. The supersonic exhaust diffuser, a main part of high-altitude test facility, provides the required test cell vacuum conditions by self-pumping the nozzle exhaust gases to the atmosphere. However, the plume temperature is often much higher than the temperature the diffuser structure is able to withstand, usually above 2500 K. In this study, an efficient cooling system is designed and analyzed to resolve the thermal problem. A water spray cooling technique is preferred among various existing techniques. Here, a new algorithm is developed for a spray cooling system for a supersonic exhaust...
Supersonic inlet buzz detection using pressure measurement on wind tunnel wall
, Article Aerospace Science and Technology ; Volume 86 , 2019 , Pages 782-793 ; 12709638 (ISSN) ; Daliri, A ; Sepahi Younsi, J ; Sharif University of Technology
Elsevier Masson SAS
2019
Abstract
Feasibility of an innovative buzz detection technique through measuring the static pressure outside a mixed-compression supersonic inlet is studied. The buzz is an instability phenomenon that occurs almost in all supersonic inlets. During the buzz, shock oscillation along with pressure and mass flow fluctuations affects the performance characteristics of the inlet. The main objective of this paper is to introduce a simple and easy-to-implement method for investigation of the buzz phenomenon in a supersonic inlet. The experimental data for far field-based are compared with those of the model-based one at free stream Mach numbers of 1.8, 2.0, and 2.2 and at zero degrees angle of attack for a...
Modeling of forced vibration of marine structural systems under dynamic loads of sea waves
, Article 18th Australasian Coastal and Ocean Engineering Conference 2007, COASTS 2007 and the 11th Australasian Port and Harbour Conference 2007, PORTS 2007, Melbourne, VIC, 18 July 2007 through 20 July 2007 ; 2007 , Pages 560-565 ; 9781622764280 (ISBN) ; Kanani, A ; Farahani, R. J ; Sharif University of Technology
2007
Abstract
Predicting the reaction and function of marine structures towards sea waves, is of significant importance in the design of them. There are some uncertain parameters which can be optimized to increase safety factors as well as to decrease the costs. Knowing the maximum oscillation of marine structures due to dynamic forces will play a great role on structures' safe design. The objective of this paper is to employ a reliable numerical technique to analyze the interaction between marine structures and sea waves. Simulink is an object oriented dynamic simulation package. It can develop new analysis tools aimed at a better understanding and prediction of the physics that governs the behavior of...
Melt preparation and investigation of properties of toughened Polyamide 66 with SEBS-g-MA and their nanocomposites
, Article Materials and Design ; Volume 29, Issue 1 , 2008 , Pages 105-111 ; 02613069 (ISSN) ; Ahmad Ramazani, S. A ; Sharif University of Technology
Elsevier Ltd
2008
Abstract
Polyamide 66/SEBS-g-M alloys and their nanocomposites were prepared by melt compounding using a twin screw extruder. The mechanical properties, rheological behavior and morphology of these alloys and their nanocomposites were investigated. Morphological investigations with different methods show pseudo-one-phase type morphology for these prepared alloys at all percentage of rubber. Impact and tensile tests results showed that rubber toughened samples exhibit significantly more impact strength and elongation at break comparing to virgin Polyamide. Samples with 20% of rubber show impact strength about 15 times and elongation at yield several times more than those of virgin Polyamide. So, these...
Development of an inverse finite element method with an initial guess of linear unfolding
, Article Finite Elements in Analysis and Design ; Vol. 79, issue , 2014 , p. 1-8 ; Bostan Shirin, M ; Assempour, A ; Sharif University of Technology
2014
Abstract
An inverse finite element method (IFEM) has been developed for estimation of the blank size and prediction of the strain distribution in sheet metal forming. In the inverse method the nodal coordinates in the final shape are known and their corresponding positions on the initial blank should be determined. The developed method deals with logarithmic large strains of membrane triangular elements, virtual work principle and a new approach for friction modeling. This method leads to a system of nonlinear equations which is highly sensitive to the initial guess. In order to avoid the converging problems, especially in the quasi-vertical walls, an appropriate initial guess is introduced. The...
Experimental investigation and process intensification of barium sulfate nanoparticles synthesis via a new double coaxial spinning disks reactor
, Article Chemical Engineering and Processing: Process Intensification ; Volume 115 , 2017 , Pages 11-22 ; 02552701 (ISSN) ; Shahrokhi, M ; Molaei Dehkordi, A ; Sharif University of Technology
Elsevier B.V
2017
Abstract
In this article, a new double spinning disks reactor (DSDR) has been proposed and tested successfully for the synthesis of barium sulfate nanoparticles by means of the reactive precipitation. The proposed DSDR consists of two coaxial rotating disks placed horizontally in a cylindrical chamber. Continuous precipitation of barium sulfate nanoparticles as a chemical test system was carried out using this new contacting device and the effects of operating and design parameters such as the disk rotational speed, distance between the disks, feed concentration, feed flow rate, free ion ratio, feed location, and feed distribution pattern on the mean size, size distribution, and morphology of the...
Effect of seawater on pull-out behavior of glued-in single rods set parallel to the grain of timber joints
, Article Construction and Building Materials ; Volume 222 , 2019 , Pages 342-357 ; 09500618 (ISSN) ; Majdabadi Farahani, E ; Vatani Oskouei, A ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This paper experimentally investigates the effects of seawater on pull-out behavior of single rods glued in timber parallel to grain. Considering different rod diameters (6, 8, 10 mm), slenderness ratios (7.5, 10, 15), rebar materials (steel and GFRP), and immersion time in seawater (0, 10, 20, 30, 60, 90 days), 324 specimens were tested. Mean strength reduction about 39 and 55 percent was observed for 90-day immersed joints constructed with GFRP and steel rebars, respectively. Rebar diameter and slenderness ratio significantly influenced ultimate loads, and dominant failure mode was at adhesive/timber interface. Finally, two novel strength models were developed empirically. © 2019 Elsevier...
Mixing in a novel double coaxial spinning disks reactor
, Article Chemical Engineering and Processing - Process Intensification ; Volume 159 , February , 2020 ; Molaei Dehkordi, A ; Bagheri Farahani, H ; Sharif University of Technology
Elsevier B. V
2020
Abstract
High mixing efficiency that is of great importance in various industrial processes is a significant feature of spinning disk reactors. This work was focused on the characterization of mixing in a new reactor called Double Spinning Disk Reactor (DSDR) by adopting a competitive parallel reaction system known as iodide–iodate test reaction. The proposed DSDR consists of two coaxial rotating disks that the feeds are introduced into the gap between them. The mixing improves with an increase in the rotational speed of the disk, the radial distance of the feed introduced through the lower disk, and its number of feed points, while an increase in each of the feed flow rate and the distance between...