Simulation of Natural Convection Inside an Enclosure with Several Heated Bodies

, M.Sc. Thesis Sharif University of Technology Sepahi, Farzan (Author) ; Nouri, Ali (Supervisor)

Abstract

in this study, turbulent natural convection inside an air filled square cavity with several hot and cold internal bodies in the range of Rayleigh numbers between 1010 and 1012 has been investigated numerically. Vertical walls of the enclosure have been considered isothermal and horizontal walls are insulated in all cases. An appropriate arrangement of internal bodies in which the minimum heat transfer occurs is desired. For this purpose, two dimensional Reynolds-averaged Navier-Stokes equations have been solved with the finite volume discretization method in a staggered grid. In addition, two equation high-Reynolds-number model with standard wall functions is used to simulate the...

A Hybrid Approach of Similarity-based and Scenario-based Algorithms in Alert Correlation

, M.Sc. Thesis Sharif University of Technology Sepahi, Ahmad (Author) ; Jalili, Rasoul (Supervisor)

Abstract

The rapid growth and increase in complexity of modern network and communication systems have made a demand for protecting organizations’ sensitive data and resources from malicious intrusions. Attackers and intruders perform malicious attacks by exploiting vulnerabilities, weaknesses, and flaws in computer systems using novel and advanced techniques. Traditional security mechanisms, such as authentication, access control, and firewall cannot prevent these attacks. Therefore, Intrusion detection systems (IDSs) are employed to detect abnormal activities and monitor network traffic and hosts’ events. These systems suffer from several limitations, including generating a huge amount of alerts and...

Boundary layer suction for high-speed air intakes: A review

, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; 2018 ; 09544100 (ISSN) Sepahi Younsi, J ; Forouzi Feshalami, B ; Maadi, S. R ; Soltani, M. R ; Sharif University of Technology

SAGE Publications Ltd 2018

Abstract

The paper summarizes recent developments in boundary layer suction for high-speed air intakes. Bleed has been efficiently used in supersonic and hypersonic intakes for three primary reasons: to improve the performance of the intake, to reduce the starting Mach number of the intake, and to postpone the onset of buzz oscillations. A bleed system has many characteristics such as the bleed entrance and exit areas, bleed entrance slant angle and position, and bleed type (slot or porous and ram-scoop or flush). Each of these parameters has significant impacts on the intake performance and stability that have been reviewed in this study. In addition, the effectiveness of other flow control methods...

Boundary layer suction for high-speed air intakes: A review

, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 233, Issue 9 , 2019 , Pages 3459-3481 ; 09544100 (ISSN) Sepahi Younsi, J ; Forouzi Feshalami, B ; Maadi, S. R ; Soltani, M. R ; Sharif University of Technology

SAGE Publications Ltd 2019

Abstract

The paper summarizes recent developments in boundary layer suction for high-speed air intakes. Bleed has been efficiently used in supersonic and hypersonic intakes for three primary reasons: to improve the performance of the intake, to reduce the starting Mach number of the intake, and to postpone the onset of buzz oscillations. A bleed system has many characteristics such as the bleed entrance and exit areas, bleed entrance slant angle and position, and bleed type (slot or porous and ram-scoop or flush). Each of these parameters has significant impacts on the intake performance and stability that have been reviewed in this study. In addition, the effectiveness of other flow control methods...

Novel method for supersonic inlet buzz measurement in wind tunnel

, Article Journal of Propulsion and Power ; Volume 34, Issue 1 , 2018 , Pages 273-277 ; 07484658 (ISSN) Daliri, A ; Farahani, M ; Sepahi Younsi, J ; Sharif University of Technology

American Institute of Aeronautics and Astronautics Inc 2018

Supersonic inlet buzz detection using pressure measurement on wind tunnel wall

, Article Aerospace Science and Technology ; Volume 86 , 2019 , Pages 782-793 ; 12709638 (ISSN) Farahani, M ; 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...

Performance investigation of a supersonic air intake in presence of boundary-layer bleed

, Article 32nd AIAA Applied Aerodynamics Conference ; June , 2014 Soltani, M. R ; Javad Sepahi, Y ; Daliri, A ; Sharif University of Technology

2014

Abstract

The performance of an axisymmetric supersonic mixed-compression air intake has been investigated experimentally. The intake has been designed for free stream Mach number of 2.0. This study has two main goals, firstly to investigate the performance of the intake without boundary-layer bleed in design and off-design conditions and secondly to study the effects of a slot bleed on the intake performance. The intake has been tested at free stream Mach numbers of 1.8, 2.0, and 2.2 and zero degree angle of attack. Total pressure recovery (TPR), mass flow ratio (MFR) and flow distortion (FD) have been selected parameters to assess the intake performance. The bleed slot is located upstream of the...

Performance study of a supersonic inlet in the presence of a heat source

, Article Scientia Iranica ; Volume 18, Issue 3 B , 2011 , Pages 375-382 ; 10263098 (ISSN) Soltani, M. R ; Farahani, M ; Sepahi Younsi, J ; Sharif University of Technology

2011

Abstract

The flow over a supersonic inlet has been investigated experimentally and numerically at a free stream Mach number of 2 and a zero degree angle of attack. Wind tunnel tests were performed to obtain the performance parameters of the inlet and were used as a baseline and validation tools for the numerical code. A heat source was added to the flow field at a distance ahead of the inlet. The effect of heat source addition on the main performance parameters of the inlet is investigated numerically. Results show that the heat source considerably reduces drag coefficient; however, its effect on pressure recovery is not favorable. This unfavorable effect was then minimized by controlling heat source...

Performance improvement of a supersonic external compression inlet by heat source addition

, Article World Academy of Science, Engineering and Technology ; Volume 40 , 2009 , Pages 267-274 ; 2010376X (ISSN) Soltani, M. R ; Farahani, M ; Sepahi Younsi, J ; Sharif University of Technology

2009

Abstract

Heat source addition to the axisymmetric supersonic inlet may improve the performance parameters, which will increase the inlet efficiency. In this investigation the heat has been added to the flow field at some distance ahead of an axisymmetric inlet by adding an imaginary thermal source upstream of cowl lip. The effect of heat addition on the drag coefficient, mass flow rate and the overall efficiency of the inlet have been investigated. The results show that heat addition causes flow separation, hence to prevent this phenomena, roughness has been added on the spike surface. However, heat addition reduces the drag coefficient and the inlet mass flow rate considerably. Furthermore, the...

Effects of shock wave/boundary-layer interaction on performance and stability of a mixed-compression inlet

, Article Scientia Iranica ; Volume 23, Issue 4 , 2016 , Pages 1811-1825 ; 10263098 (ISSN) Soltani, M. R ; Daliri, A ; Sepahi Younsi, J ; Sharif University of Technology

Sharif University of Technology 2016

Abstract

Experiments were conducted to study various kinds of Shock wave/Boundary Layer Interaction (SBLI) in an axisymmetric mixed-compression inlet. Experimental findings were compared and verified by numerical solutions where possible. Different types of SBLI relevant to the mixed-compression inlets are classified. Interactions of normal shock wave/boundary-layer at subcritical condition and in buzz condition are investigated using Schlieren and shadowgraph flow visualization as well as unsteady pressure recordings. The data is compared with the CFD predictions. Interactions of cowl lip reflected oblique shock and the terminal normal shock with the spike boundary-layer at both critical and...

Correlation between isothermal crystallization properties and slow crack growth resistance of polyethylene pipe materials

, Article Polymer Testing ; Volume 80 , 2019 ; 01429418 (ISSN) Gholami, F ; Pircheraghi, G ; Rashedi, R ; Sepahi, A ; Sharif University of Technology

Elsevier Ltd 2019

Abstract

In this study, three PE100 polyethylene materials with fairly different short chain branch distributions were used to characterize the relation between thermal properties and creep test failure time. The samples were thermally characterized using isothermal and non-isothermal differential scanning calorimetry (DSC). The three resins showed different behavior after fitting on the Avrami equation. N-100J2 sample, in which short chain branches (SCBs) are located on longer molecule chains, has a lower chain mobility and higher crystallization time, while N-100J1 has the opposite crystallization properties. Also, these samples had different Avrami index, n. Microstructural evaluation of these...

A novel upper-limb rehabilitation robot with 4 DOFs: design and prototype

, Article Proceedings of the 6th RSI International Conference on Robotics and Mechatronics, IcRoM 2018, 23 October 2018 through 25 October 2018 ; 2019 , Pages 434-438 ; 9781728101279 (ISBN) Sepahi, S ; Hashemi, A ; Jafari, M ; Sharifi, M ; Sharif University of Technology

Institute of Electrical and Electronics Engineers Inc 2019

Abstract

In recent years, robotic rehabilitation has been utilized in treatment and recovery of patients with disabilities. In this paper, a novel design and kinematic analysis of a 4-DOF robot for upper-limb rehabilitation are proposed. The main novelty of this design is its mechanism for wrist and fingers motions which is added to the shoulder and elbow mechanism without any noticeable weight increase in the moving parts of the robot. For this purpose, a cable driven mechanism is implemented at the robot end-effector to move the wrist and fingers parts, and the corresponding actuators are placed at the base of the robot. © 2018 IEEE

Numerical and Experimental Investigation of Supersonic Flow in an Axisymmetric Inlet

, M.Sc. Thesis Sharif University of Technology Sepahi Younsi, Javad (Author) ; Soltani, Mohammad Reza (Supervisor)

Abstract

No considerable investigation of inlet aerodynamics has been done in our country up to now. Some numerical study in this field has been accomplished without any experimental test. To solve the inner and outer flow field of the inlet in this investigation, the numerical methods has been used and also experimental tests for code validation has been done. The inlet is an axisymmetric external compression one. In the numerical simulation the Navier-Stokes equations with explicit finite volume method have been used to model the axisymmetric, steady and turbulent flow field of the inlet in a structured grid. Viscous fluxes with a finite volume method, molecular viscosity coefficient with the...

Axisymmetric and three-dimensional flow simulation of a mixed compression supersonic air inlet

, Article Propulsion and Power Research ; Volume 9, Issue 1 , 2020 , Pages 51-61 Abedi, M ; Askari, R ; Sepahi Younsi, J ; Soltani, M. R ; Sharif University of Technology

Elsevier Ltd 2020

Abstract

The flow through an axisymmetric supersonic mixed-compression air inlet has been simulated numerically to investigate the effects and the necessity of the three-dimensional (3D) modeling in comparison with the axisymmetric one. For this purpose, a supersonic inlet has been simulated numerically via axisymmetric and 3D CFD solvers, using the steady state Reynolds-averaged Navier-Stokes equations along with the SST k-ω turbulence model, for a free-stream Mach number of 2.0 and at zero degrees angle of attack. The grid for the 3D cases was a 14.4-degree sector, instead of a 360-degree domain one, with rotational periodic boundary condition for the side boundaries. The results show that both...

Experimental Investigation of Buzz Phenomenon Suppression in a Supersonic Air Intake

, Ph.D. Dissertation Sharif University of Technology Sepahi Younsi, Javad (Author) ; Soltani, Mohammad Reza (Supervisor) ; Farahani, Mohammad (Co-Advisor)

Abstract

The buzz phenomenon is the shock oscillation ahead of the supersonic air intake when its mass flow rate is decreasing at subcriticaloperating condition. This phenomenon may cause combustion extinguishing, thrust loss and structural damages. To delay the buzz onset and reduce the amplitude and frequency of the buzz oscillations, the method of boundary layer suction has been proposed and studied in this research. The intake has been designed for a freestream Mach number of 2.0, however, wind tunnel tests have been conducted for freestream Mach numbers of 1.8, 2.0, and 2.2. All tests were performed for zero degrees angle of attack. For studying effects of the parameters of boundary layer...

Signal amplification of a quartz crystal microbalance immunosensor by gold nanoparticles-polyethyleneimine for hepatitis B biomarker detection

, Article Scientific Reports ; Volume 13, Issue 1 , 2023 ; 20452322 (ISSN) Saffari, Z ; Cohan, R. A ; Sepahi, M ; Sadeqi, M ; Khoobi, M ; Fard, M. H ; Ghavidel, A ; Amiri, F. B ; Aghasadeghi, M. R ; Norouzian, D ; Sharif University of Technology

Nature Research 2023

Abstract

The procedures currently used for hepatitis B (HB) detection are not suitable for screening, clinical diagnosis, and point-of-care testing (POCT). Therefore, we developed and tested a QCM-based immunosensor by surface modification with AuNP-PEIs to amplify the signal and provide an oriented-immobilization surface. The AuNP-PEIs were characterized by ICP-Mass, UV/Vis, DLS, FE-SEM, and ATR-FTIR. After coating AuNP-PEIs on the gold electrode surface, anti-HBsAg antibodies were immobilized using NHS/EDC chemistry based on response surface methodology (RSM) optimization. The efficiency of the immunosensor was assessed by human sera and data were compared to gold-standard ELISA using...

The relationship between an EFL teacher's gender and students' willingness to communicate

, Article International Journal of Communication and Linguistic Studies ; Volume 10, Issue 4 , 2013 , Pages 17-29 ; 23277882 (ISSN) Khosravizadeh, P ; Pakzadian, S. S

Common Ground Publishing 2013

Abstract

Learning a foreign language encompasses a process of trial and error that can lead to the progression of the learner's interlanguage, meaning that the learners make use of their language knowledge that receives feedback and brings about progress through diagnosis of the problems and being corrected by the teacher. Therefore, there exists a need to analyze the underlying reasons causing the students to remain taciturn with a low willingness to communicate (WTC) during a language class. There has been much work done investigating the role of the learner's stable personal characteristics (traits) along with their situational changes at a specific time (states) that influence the student's...

An automated simple algorithm for realistic pore network extraction from micro-tomography images

, Article Journal of Petroleum Science and Engineering ; Vol. 123, issue , 2014 , pp. 164-171 ; ISSN: 09204105 Rabbani, A ; Jamshidi, S ; Salehi, S

2014

Abstract

Using 3-D scanned data to analyze and extract pore network plays a vital role in investigation of porous media's characteristics. In this paper, a new simple method is developed to detect pores and throats for analyzing the connectivity and permeability of the network. This automated method utilizes some of the common and well-known image processing functions which are widely accessible by researchers and this has led to an easy algorithm implementation. In this method, after polishing and quality control of images, using city-block distance function and watershed segmentation algorithm, pores and throats are detected and 3-D network is produced. This method can also be applied on 2-D images...

Discrimination of heart arrhythmias using novel features in heart rate phase space

, Article Computing in Cardiology ; Volume 40 , Sept , 2013 , Pages 1035-1038 ; 23258861 (ISSN); 9781479908844 (ISBN) Moharreri, S ; Rezaei, S ; Salavatian, S

2013

Abstract

In this paper, we try to recognize and distinguish different groups of arrhythmia using novel features which have been obtained from the heart rate's phase space in recent years. For this purpose, we used Triangular Phase Space Mapping (TPSM) and Parabolic Phase Space Mapping (PPSM). For recognition, we used three groups of 15 subjects using the Physionet database (Arrhythmia, Congestive Heart Failure (CHF), and Atrial Fibrillation (AF)) with Normal Sinus Rhythm (NSR). The obtained features discriminate arrhythmia from NSR by p

An intelligent hybrid classification algorithm integrating fuzzy rule-based extraction and harmony search optimization: Medical diagnosis applications

, Article Knowledge-Based Systems ; Volume 220 , 2021 ; 09507051 (ISSN) Mousavi, S. M ; Abdullah, S ; Akhavan Niaki, S. T ; Banihashemi, S ; Sharif University of Technology

Elsevier B.V 2021

Abstract

Uncertainty is a critical factor in medical datasets needed to be overcome for increasing diagnosis efficiency. This paper proposes an intelligent classification algorithm comprising a fuzzy rule-based approach, a harmony search (HS) algorithm, and a heuristic algorithm to classify medical datasets intelligently. Two fuzzy approaches, as well as orthogonal and triangular fuzzy sets, are first utilized to define the attributes of data. Then, an HS algorithm is integrated with a heuristic to generate fuzzy rules to select the best rules in the fuzzy rule-based systems. Moreover, to improve the performance of the proposed classification approach, a three-phase parameter tuning approach is...