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sepahi--ahmad
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Simulation of Natural Convection Inside an Enclosure with Several Heated Bodies
, M.Sc. Thesis Sharif University of Technology ; 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 ; 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...
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) ; 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) ; 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 ; 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) ; 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) ; 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) ; 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) ; 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) ; 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 ; 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 ; 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...
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) ; 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) ; 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...
Experimental Investigation of Buzz Phenomenon Suppression in a Supersonic Air Intake
, Ph.D. Dissertation Sharif University of Technology ; 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...
Manufacture of Smart Drug Delivery System with UCST Polymers
, M.Sc. Thesis Sharif University of Technology ; Ramazani, Ahmad (Supervisor)
Abstract
Smart heat-sensitive polymers play a unique role in drug delivery systems due to reversible behavior in response to environmental changes, especially temperature changes. Among the heat-sensitive polymers, UCST polymers due to their specific behavior and very little-known polymers with this feature are the subject of many new researches. In the present study, New designed temperature-sensitive polymers with UCST capability based on acrylamide and vinyl acetate were synthesized. These copolymers were synthesized in different percentages of acrylamide by free radical polymerization in solution conditions. All polymers compounds were characterized by H-NMR, FT-IR, DSC and GPC measurements. The...
Numerical study of lorentz force interaction with micro structure in channel flow
, Article Energies ; Volume 14, Issue 14 , 2021 ; 19961073 (ISSN) ; Ali, K ; Ahmad, S ; Cai, J ; Sharif University of Technology
MDPI AG
2021
Abstract
The heat transfer Magnetohydrodynamics flows have been potentially used to enhance the thermal characteristics of several systems such as heat exchangers, electromagnetic casting, adjusting blood flow, X-rays, magnetic drug treatment, cooling of nuclear reactors, and magnetic devices for cell separation. Our concern in this article is to numerically investigate the flow of an incompressible Magnetohydrodynamics micropolar fluid with heat transportation through a channel having porous walls. By employing the suitable dimensionless coordinates, the flow model equations are converted into a nonlinear system of dimensionless ordinary differential equations, which are then numerically treated for...
A numerical approach for analyzing the electromagnetohydrodynamic flow through a rotating microchannel
, Article Arabian Journal for Science and Engineering ; Volume 48, Issue 3 , 2023 , Pages 3765-3781 ; 2193567X (ISSN) ; Ahmad, A ; Ahmad, S ; Ahmad, S ; Jamshed, W ; Sharif University of Technology
Institute for Ionics
2023
Abstract
The purpose of the paper is to develop a mathematical foundation for exploring the complex interaction of Coriolis and Lorentz forces with the electromagnetohydrodynamic (EMHD) flow of a power-law fluid inside a microchannel with wall slip condition. Both the Lorentz and Coriolis forces act orthogonally to each other. Mathematical modeling of the problem is based on a set of classical Maxwell and Navier–Stokes equations, which are subsequently solved numerically by employing an implicit finite difference methodology. The numerical solution thus obtained has been found to be in an excellent agreement correlation with the ones reported in the scientific literature, for some limiting cases. A...
A self-similar approach to study nanofluid flow driven by a stretching curved sheet
, Article Symmetry ; Volume 14, Issue 10 , 2022 ; 20738994 (ISSN) ; Jamshed, W ; Ahmad, S ; Bashir, H ; Ahmad, S ; Tag El Din, E.S.M ; Sharif University of Technology
MDPI
2022
Abstract
Nano-fluids have considerable importance in the field of thermal development that relates to several industrial systems. There are some key applications in recent construction systems flow, as well as microscale cooling gadgets and microstructure electric gadgets for thermal migration. The current investigation concludes the study of electrically conducting nano-fluid flow and heat transfer analysis in two-dimensional boundary layer flow over a curved extending surface in the coexisting of magnetic field, heat generation and thermal radiation. The small sized particles of copper (Cu) are taken as nanoparticles and water is assumed to be the base fluid. We used quasi-linearization and central...
Thin Film Thickness Measurement Using Colors of Interference Fringes
, M.Sc. Thesis Sharif University of Technology ; Amjadi, Ahmad (Supervisor)
Abstract
There are several methods for measuring thin film thickness, however, for the analysis of liquid film motors [1] we need a method which is capable of measuring the thickness using a single image of the film. In this work, we use the colors that appear on thin films, such as soup bubbles, which is a result of light interference to calculate the thickness of the layer