Drag reduction by a multi-point optimised hybrid flow control method for two supercritical airfoils

, Article European Journal of Computational Mechanics ; Volume 25, Issue 5 , 2016 , Pages 359-387 ; 17797179 (ISSN) Nejati, A ; Mazaheri, K ; Sharif University of Technology

Taylor and Francis Ltd 2016

Abstract

Shock control bump (SCB), suction and blowing are three flow control methods used to control the shock wave/boundary layer interaction to reduce the resulting wave drag in transonic flows. An SCB uses a small local surface deformation to reduce the shock wave strength, while the suction decreases the boundary layer thickness and the blowing delays the flow separation. Here, we will use a multi-point continuous adjoint optimisation scheme to find the optimum design of suction and blowing separately or together, or with the SCB, on two supercritical airfoils, i.e. RAE-5225 and RAE-2822, for a wide range of off-design transonic Mach numbers. The RANS flow equations are solved using the Roe’s...

Performance improvement of a supercritical airfoil by a multi-point optimized shock control channel

, Article Flow, Turbulence and Combustion ; 2017 , Pages 1-29 ; 13866184 (ISSN) Nejati, A ; Mazaheri, K ; Sharif University of Technology

2017

Abstract

A shock control channel (SCC) is a flow control method introduced here to control the shock wave/boundarylayer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. An SCC transfers an appropriate amount of mass and momentum from downstream of the shock wave location to its upstream to decrease the pressure gradient across the shock wave and as a result the shock-wave strength is reduced. Here, a multi-point optimization method under a constant-lift-coefficient constraint is used to find the optimum design of the SCC. This flow control method is implemented on a RAE-2822 supercritical airfoil for a wide range of off-design transonic Mach numbers. The RANS flow...

Application of the adjoint optimisation of shock control bump for ONERA-M6 wing

, Article European Journal of Computational Mechanics ; Volume 26, Issue 5-6 , 2017 , Pages 557-583 ; 17797179 (ISSN) Nejati, A ; Mazaheri, K ; Sharif University of Technology

2017

Abstract

This article is devoted to the numerical investigation of the shock wave/boundary layer interaction (SWBLI) as the main factor influencing the aerodynamic performance of transonic bumped airfoils and wings. The numerical analysis is conducted for the ONERA-M6 wing through a shock control bump (SCB) shape optimisation process using the adjoint optimisation method. SWBLI is analyzed for both clean and bumped airfoils and wings, and it is shown how the modified wave structure originating from upstream of the SCB reduces the wave drag, by improving the boundary layer velocity profile downstream of the shock wave. The numerical simulation of the turbulent viscous flow and a gradient-based adjoint...

Performance improvement of a supercritical airfoil by a multi-point optimized shock control channel

, Article Flow, Turbulence and Combustion ; Volume 100, Issue 3 , 2018 , Pages 675-703 ; 13866184 (ISSN) Nejati, A ; Mazaheri, K ; Sharif University of Technology

Springer Netherlands 2018

Abstract

A shock control channel (SCC) is a flow control method introduced here to control the shock wave/boundarylayer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. An SCC transfers an appropriate amount of mass and momentum from downstream of the shock wave location to its upstream to decrease the pressure gradient across the shock wave and as a result the shock-wave strength is reduced. Here, a multi-point optimization method under a constant-lift-coefficient constraint is used to find the optimum design of the SCC. This flow control method is implemented on a RAE-2822 supercritical airfoil for a wide range of off-design transonic Mach numbers. The RANS flow...

Aerodynamic Optimization of Transonic Airfoils and Wings by Using Shock Control Bump, Suction and Blowing with Adjoint Method

, Ph.D. Dissertation Sharif University of Technology Nejati, Ashkan (Author) ; Mazaheri, Karim (Supervisor)

Abstract

Shock control bump (SCB) and suction and blowing are flow control methods used to control the shock wave/boundary layer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. A SCB uses a small local surface deformation to reduce the shock-wave strength, while suction decreases the boundary-layer thickness and blowing delays the flow separation. Here, a single-point, a multi-point, and a robust optimization method are used to find the optimum design of SCB and suction and blowing. The flow control methods are used separately or together on two transonic airfoils i.e.; RAE-2822 and NACA-64A010 for a wide range of off-design transonic Mach numbers. The RANS flow...

Categorization of Software Repositories in Version Control Systems

, M.Sc. Thesis Sharif University of Technology Nejati, Mahtab (Author) ; Heydarnoori, Abbas (Supervisor)

Abstract

Developers often seek to find projects that match their topics of interest in version control systems with the goal of reusing code, extracting similar requirements, learning, and more. However, due to the widespread use of these systems, the number of projects maintained on them is huge and ever-increasing. This has made it difficult to identify projects based on their topics. GitHub, as a prominent version control system, with the aim of facilitating access to projects based on their topics, has provided the possibility of assigning software topics to projects in the form of free-text tags for users. Assigning a correct and complete set of topics to software projects allows programmers to...

Experimental Study on the Influence of Connections Rigidity in Steel Moment-Resisting Frames Under Fire Loading

, M.Sc. Thesis Sharif University of Technology Nejati, Shahin (Author) ; Khonsari, Vahid (Supervisor)

Abstract

The present study evaluates the effect of connection rigidity on the behaviour of partially restrained frames under fire condition. Since the interaction of members with each other at elevated temperatures, controlled by the connections, has a significant effect on the behavior of the structure, a half-scaled three dimensional one-bay, one-story frame was used as the test specimen. In fact, this study is part of a broader research programme in which identical specimens equipped with similar connections (flush endplate connections) with various thicknesses hence various rigidities are studied. In order to record the deformations of structural members and the rotation of connections, Digital...

Comparison between backstepping and input-output linearization techniques for pH process control

, Article Journal of Process Control ; Volume 22, Issue 1 , 2012 , Pages 263-271 ; 09591524 (ISSN) Nejati, A ; Shahrokhi, M ; Mehrabani, A ; Sharif University of Technology

2012

Abstract

In this work performances of adaptive backstepping controller (BSC) and globally linearizing controller (GLC) are compared for pH control. First, based on the system full order model a GLC has been designed and it has been shown that this controller is identical to BSC proposed in the literature. Next in order to avoid state estimator design, BSC and GLC are designed based on pH reduced order model and their identities have been established. Through computer simulations, it has been shown that the performance of non-adaptive GLC designed based on reduced order model is better than that of adaptive BSC designed based on pH full order model which requires state measurement for implementation....

Multivariable control strategy for autonomous operation of a converter-based distributed generation system

, Article 2011 IEEE/PES Power Systems Conference and Exposition, PSCE 2011, 20 March 2011 through 23 March 2011, Phoenix, AZ ; March , 2011 , Page(s): 1 - 8 ; 9781612847870 (ISBN) Nejati, A ; Nobakhti, A ; Karimi, H ; Sharif University of Technology

2011

Abstract

This paper presents a control strategy for the autonomous (islanded) operation of a distributed generation (DG) unit. The DG unit supplies a balanced load through a voitage-sourced converter (VSC). To maintain the autonomous operation in the islanded mode, the DG unit should provide its dedicated load with a sinusoidal voltage with a constant magnitude and a constant frequency. The dynamic model of the islanded DG system is represented by a set of nonlinear equations. Since the objective is to regulate voltage and frequency of the islanded DG about their rated values, the nonlinear model is linearized about the operating point. The obtained linearized model represents a multivariable LTI...

A two-dimensional approach to evaluate the scientific production of countries (case study: The basic sciences)

, Article Scientometrics ; Volume 84, Issue 2 , 2010 , Pages 357-364 ; 01389130 (ISSN) Nejati, A ; Hosseini Jenab, S. M ; Sharif University of Technology

2010

Abstract

The quantity and quality of scientific output of the topmost 50 countries in the four basic sciences (agricultural & biological sciences, chemistry, mathematics, and physics & astronomy) are studied in the period of the recent 12 years (1996-2007). In order to rank the countries, a novel two-dimensional method is proposed, which is inspired by the H-index and other methods based on quality and quantity measures. The countries data are represented in a "quantity-quality diagram", and partitioned by a conventional statistical algorithm into three clusters, members of which are rather the same in all of the basic sciences. The results offer a new perspective on the global positions of countries...

Adaptive nonlinear control of pH neutralization processes using fuzzy approximators

, Article Control Engineering Practice ; Volume 17, Issue 11 , 2009 , Pages 1329-1337 ; 09670661 (ISSN) Salehi, S ; Shahrokhi, M ; Nejati, A ; Sharif University of Technology

2009

Abstract

In this paper, an adaptive control scheme, based on fuzzy logic systems, for pH control is addressed. For implementation of the proposed scheme no composition measurement is required. Stability of the closed-loop system is established and it is shown that the solution of the closed-loop system is uniformly ultimately bounded and under a certain condition, asymptotical stability is achieved. Effectiveness of the proposed controller is tested through simulation and experimental studies. Results indicate that the proposed controller has good performances in set-point tracking and load rejection and much better than that of a tuned PI controller. © 2009 Elsevier Ltd. All rights reserved

Adaptive input-output linearization control of pH processes

, Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 27, Issue 3 , 2008 , Pages 25-35 ; 10219986 (ISSN) Nejati, A ; Shahrokhi, M ; Mehrabani, A ; Sharif University of Technology

2008

Abstract

pH control is a challenging problem due to its highly nonlinear nature. In this paper the performances of two different adaptive global linearizing controllers (GLC) are compared. Least squares technique has been used for identifying the titration curve. The first controller is a standard GLC based on material balances of each species. For implementation of this controller a nonlinear state estimator is used. Some modifications are proposed to avoid the singularity of the observer gain. The second controller is designed based on the reduced state equation. Through computer simulations, it has been shown that the performances of the second GLC is superior and it is more robust to process...

Response Time Improvement Using Service Migration in Mobile Edge Computing Considering User Mobility

, M.Sc. Thesis Sharif University of Technology Nejati, Amir Reza (Author) ; Goudarzi, Maziar (Supervisor)

Abstract

With the emergence of the 5th generation cellular networks, response time is becoming increasingly more important. One of the solutions to satisfy this requirement is using mobile edge computing. MEC is bringing the cloud computing features to the edge of the network and reduces services response time by reducing the user distance to her services. But for this solution to be effective, we need to migrate user services based on their movements. The main problem in migrating services is predicting user route and do the migration based on these predictions. We must do this procedure in a way that minimizes the service outage. In this research, we predict the user route with the historical...

Hierarchical Optical Network-on-Chip Based on Hypercube Topology

, M.Sc. Thesis Sharif University of Technology Abdollahi, Meisam (Author) ; Hesabi, Shahin (Supervisor)

Abstract

According to prediction of ITRS, power consumption and bandwidth of processors' interconnection, will be the most major bottleneck of the System-on- Chips (SoCs) in the future. Therefore, in MultiProcessor System-on-Chip (MPSoC) architectures, the design constraints will be altered from "Computational Constraints" to "Communicational Constraints". There are three kinds of communications in the surface of the chip: Global, median and local. The main difference between global and local connections is that the length of latter one will be changed with technology. In other words, it is scalable like processor's elements while the length of global connections is practically constant. Even though...

Architecture of Reconfigurable Optical Network-on-Chip

, M.Sc. Thesis Sharif University of Technology Falahati, Hajar (Author) ; Hesabi, Shahin (Supervisor)

Abstract

According to power limitation on a chip and the need to simultaneously access high utilization and low power consumption, Multi-Processor System-on-Chip (MPSoC) architectures have been introduced. The major part of power consumption in a network on chip belongs to interconnects. One of the most important issues is to decrease power consumption while maintaining high utilization. The ability of optical interconnects in decreasing power consumption and increasing utilization has introduced a new architecture called optical network on chip. This architecture uses the benefits of optical signals and elements in order to transfer data. In this thesis, we introduce a new architecture with...

Analysis of Off-Critical Percolation Clusters by Schramm-Loewner Evolution

, M.Sc. Thesis Sharif University of Technology Jamali, Tayyeb (Author) ; Rouhani, Shahin (Supervisor)

Abstract

Recently, a new tool in the study of two-dimensional continuous phase transition was provided by Schramm-Loewner evolution. The main part of SLE is a conformal map which relates growth process of a two-dimensional simple curve to one-dimensional motion on the real axis (so-called Loewner driving function). Time evolution of this map and Loewner driving function is connected via the Loewner differential equation. It turns out that for a certain class of stochastic and conformally invariant curves in two dimensions, the driving function shows Brownian motion in one dimension. Strength point of SLE comes from this fact that all the geometrical properties of such curves is described through a...

The Watershed Model and Schramm-loewner Evolution

, Ph.D. Dissertation Sharif University of Technology Daryaei, Ebrahim (Author) ; Rouhani, Shahin (Supervisor)

Abstract

Schramm Loewner evolution (SLE) is a one-parameter family of random simple curves in the complex plane introduced by Schramm in 1999 which is believed to describe the scaling limit of a variety of domain interfaces at criticality. This thesis is concerned with statistical properties of watersheds dividing drainage basins. The fractal dimension of this model is 1.22 which is consistent with the known fractal dimension for several important models such as Invasion percolation and minimum spanning trees (MST). We present numerical evidences that in the scaling limit this model are SLE curves with =1.73, being the only known physical example of an
SLE with <2. This lies outside the...

Energy Efficient Concurrent Test of Switches and Links for Networks-On-Chip

, M.Sc. Thesis Sharif University of Technology Alamian, Sanaz (Author) ; Hessabi, Shahin (Supervisor)

Abstract

Nowadays by increasing the number of processing cores in system-on-chip, using networks-on-chip, as an optimized interconnection foundation for transferring data between processing cores is inevitable .Based on this, the necessity of designing and implementing an optimized structure for testing network-on-chip, considering various overheads such as power consumption, latency, bandwidth and area, becomes an important issue in designing network-on-chip. The purpose of this project is to design an optimized structure for testing routers and connecting links in network, which considers power consumption overhead, latency and area overhead on one hand, and fault coverage on the other hand....

High Speed CDMA Communication in Optical Network on Chip

, M.Sc. Thesis Sharif University of Technology Abdi, Mania (Author) ; Hesabi, Shahin (Supervisor)

Abstract

As the number of processing cores on a single chip continues to grow, the need for a high band width, low power communication structure, will be the most important requirements of next generation chip multiprocessors. Today, a major part of power consumption in multi core architectures belongs to interconnects. Due to these facts, reducing consuming power, as well as supporting high performance, is concerned in these architectures. The concept of “network-on-chip” emerged to improve the performance of CMPs. But now a day, considering the circumstances of power budges, it’s incapable of presenting new strategies to decrease consuming power and delay. However, optical interconnects have the...

Modified WK-Recursive Topology for an Optical Network-on-Chip

, M.Sc. Thesis Sharif University of Technology Mahdavian, Hojjat (Author) ; Hesabi, Shahin (Supervisor)

Abstract

Nowadays, a large proportion of the power consumption in high-performance multi-processor architectures on chip belongs to connections. Reducing power consumption while maintaining high efficiency in these architectures is one of the main concerns. Networks on Chip (NoC) originally were introduced to improve efficiency, but now, given the importance of power, we must provide some solutions to reduce power consumption, and delay in NOCs. Connections in chip can be divided into three categories: global, intermediate and local, while the length of global connections is almost constant in different scales, local connections are scalable. As a result improving efficiency of a small number of...