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nili-ahmadabadi--mahdi
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Centrifugal compressor shape modification using a proposed inverse design method
, Article Journal of Mechanical Science and Technology ; Volume 27, Issue 3 , 2013 , Pages 713-720 ; 1738494X (ISSN) ; Poursadegh, F ; Sharif University of Technology
2013
Abstract
This paper is concerned with a quasi-3D design method for the radial and axial diffusers of a centrifugal compressor on the meridional plane. The method integrates a novel inverse design algorithm, called ball-spine algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain, of which unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, unknown walls are composed of a set of virtual balls that move freely along specified directions called spines. The difference between target and current pressure distributions causes the flexible boundary to deform...
A novel aerodynamic design method for centrifugal compressor impeller
, Article Journal of Applied Fluid Mechanics ; Vol. 7, issue. 2 , July , 2014 , p. 329-344 ; Durali, M ; Hajilouy, A ; Sharif University of Technology
2014
Abstract
This paper describes a new quasi-3D design method for centrifugal compressor impeller. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a quasi-3D analysis. Euler equation is solved on the impeller meridional plane. The unknown boundaries (hub and shroud) of numerical domain are iteratively modified by BSA until a target pressure distribution in flow passage is reached. To validate the quasi-3D analysis code, existing compressor impeller is investigated experimentally. Comparison between the quasi-3D analysis and the experimental results shows good agreement. Also, a full 3D Navier-Stokes code is used to analyze the existing and designed compressor...
Subsonic and transonic airfoil inverse design via Ball-Spine Algorithm
, Article Computers and Fluids ; Volume 84 , 2013 , Pages 87-96 ; 00457930 (ISSN) ; Ghadak, F ; Mohammadi, M ; Sharif University of Technology
2013
Abstract
Inverse design in external flow regimes usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this research, a novel iterative inverse design method is developed for inviscid subsonic and transonic external flow regimes. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a 2D inviscid analysis code. The Euler equations are solved for a physical domain of which some unknown boundaries are iteratively modified via BSA until a prescribed pressure distribution is reached. In BSA, the unknown walls are composed of a set of virtual balls that move freely along the specified directions called...
Experimental and numerical investigation of a centrifugal compressor
, Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010, Istanbul ; Volume 3 , 2010 , Pages 447-458 ; 9780791849170 (ISBN) ; Hajilouy Benisi, A ; Nili Ahmadabadi, M ; Sharif University of Technology
2010
Abstract
In this research, centrifugal compressor of a gas turbine is investigated experimentally and numerically. Operation line of the compressor as a component of the gas turbine is obtained experimentally by measurements of impeller rotational speed, and flow parameters at the compressor inlet and outlet during the gas turbine operation. The flow field inside the impeller and diffusers are analyzed numerically using a full 3D Navier-Stokes program with SST turbulence model. Boundary conditions for the numerical simulation are specified from the experimental measurements. The operation line of the compressor is obtained numerically, which is compared with that of the experimental results, and...
A novel QUASI-3D design method for centrifugal compressor meridional plane
, Article Proceedings of the ASME Turbo Expo, 14 June 2010 through 18 June 2010 ; Volume 7, Issue PARTS A, B, AND C , 2010 , Pages 919-931 ; 9780791844021 (ISBN) ; Durali, M ; Hajilouy Benisi, A ; Sharif University of Technology
2010
Abstract
This paper is concerned with a quasi-3D design method for centrifugal compressor impeller in the meridional plane. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain of which some unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, the unknown walls are composed of a set of virtual balls that move freely along the specified directions called spines. The difference between target and current pressure distribution causes to deform flexible boundary at each modification...
Natural Vibrations of Nanostructures Using a Developed 3D Model Based on Nonlocal Theory of Elasticity
,
M.Sc. Thesis
Sharif University of Technology
;
Dehghani Firoozabadi, Rouhollah
(Supervisor)
Abstract
The goal of this thesis is to survey natural frequencis of nanostructures such as nanobeams and nanoplates using nonlocal theory of elasticity by finite element method. In nonlocal theory of elasticity,the constitutive relation appears as an integral form so that the stress of a point is a function of the strain of all points in the field such that by getting away from the assumed point, the effect of strains on the stress of that point decreases. In fact, the stress on a point is an average of stress in the field and the effect of stress of other points in determined by a function called the kernel function. In order to achieve natural frequencies and shape modes of a structure, we need to...
Duct design in subsonic and supersonic flow regimes with and without normal shock waves using Flexible String Algorithm
, Article Scientia Iranica ; Volume 17, Issue 3 B , MAY-JUNE , 2010 , Pages 179-193 ; 10263098 (ISSN) ; Durali, M ; Hajilouy Benisi, A ; Ghadak, F ; Sharif University of Technology
2010
Abstract
In this investigation, the Flexible String Algorithm (FSA) used before for the inverse design of 2D subsonic ducts is developed and applied for the inverse design of subsonic and supersonic ducts with and without normal shock waves. In this method, the duct wall shape is changed under a novel algorithm based on the deformation of a virtual flexible string in a flow. Deformation of the string due to the local fl.ow conditions resulting from changes in the wall geometry is performed until the target shape satisfying the. prescribed walls pressure distribution is achieved. The flow field at each shape modification step is analyzed using an Euler equation solution by the. A USM method. Some...
A novel 2D incompressible viscous inverse design method for internal flows using flexible string algorithm
, Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 132, Issue 3 , 2010 , Pages 0314011-03140110 ; 00982202 (ISSN) ; Hajilouy Benisi, A ; Ghadak, F ; Durali, M ; Sharif University of Technology
2010
Abstract
In this investigation, the flexible string algorithm (FSA), used before for inverse design of subsonic and supersonic ducts in compressible flows with and without normal shock, is developed and applied for inverse design of 2D incompressible viscous internal flow with and without separation. In the proposed method, the duct wall shape is changed under an algorithm based on deformation of a virtual flexible string in flow. At each modification step, the difference between current and target wall pressure distributions is applied to the string. The method is an iterative inverse design method and utilizes the analysis code for the flow field solution as a black-box. Some validation test cases...
Inverse design of 2-D subsonic ducts using flexible string algorithm
, Article Inverse Problems in Science and Engineering ; Volume 17, Issue 8 , 2009 , Pages 1037-1057 ; 17415977 (ISSN) ; Dural, M ; Hajilouy Benisi, A ; Ghadak, F ; Sharif University of Technology
2009
Abstract
The duct inverse design in fluid flow problems usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, an iterative inverse design method for 2-D subsonic ducts is presented. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall's pressure distribution is reached. The flow field at each step is analysed using Euler equations and the advection upstream splitting...
Duct design in subsonic & supersonic flow regimes with and without normal shock wave using flexible string algorithm
, Article Proceedings of the ASME Turbo Expo, 8 June 2009 through 12 June 2009, Orlando, FL ; Volume 7, Issue PART A , 2009 , Pages 513-523 ; 9780791848883 (ISBN) ; Hajilouy Benisi, A ; Durali, M ; Ghadak, F ; Sharif University of Technology
2009
Abstract
In this investigation, the Flexible String Algorithm (FSA), used before for 2D subsonic ducts inverse design, is developed and applied to inverse design of supersonic ducts with and without normal shock wave. In this method, the duct wall shape is changed under an algorithm based on deformation of a virtual flexible string in a flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is performed until the target shape satisfying the prescribed walls pressure distribution is achieved. The flow field at each step is analyzed using Euler equations solutions by the AUSM method. Some validation test cases and design examples in subsonic and...
Investigation of a centrifugal compressor and study of the area ratio and TIP clearance effects on performance
, Article Journal of Thermal Science ; Volume 17, Issue 4 , December , 2008 , Pages 314-323 ; 10032169 (ISSN) ; Hajilouy Benisi, A ; Durali, M ; Ghadak, F ; Sharif University of Technology
2008
Abstract
In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was...
Experimental & numerical investigation of a centrifugal compressor and numerical study of the area ratio and tip clearance effects on the performance characteristic
, Article 2008 ASME Turbo Expo, Berlin, 9 June 2008 through 13 June 2008 ; Volume 6, Issue PART B , 2008 ; 9780791843161 (ISBN) ; Hajilouy Benisi, A ; Durali, M ; Motavalli, S. M ; Sharif University of Technology
American Society of Mechanical Engineers(ASME)
2008
Abstract
In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was...
Experimental and theoretical investigation of centrifugal compressor performance characteristics
, Article Proceedings of the ASME Turbo Expo, 9 June 2008 through 13 June 2008, Berlin ; Volume 6, Issue PART B , 2008 ; 9780791843161 (ISBN) ; Hajilouy Benisi, A ; Nili Ahmadabadi, M ; International Gas Turbine Institute ; Sharif University of Technology
2008
Abstract
Prediction of compressor performance is a basic step in design of this turbomachine, while designer can optimize plan by considering various conditions and calculating machine performance. Flow field in centrifugal compressor is threedimensional and intricate. Since 2-D and 3-D methods are very costly, consequently the mean line method usually is used for predicting compressor performance. The energy loss coefficients are used for this method. Because of the intricacy in flow and analysis of losses, most energy loss coefficients are attained by experimental procedures, however just some of them are determined according to theory and nature of the flow field. The purpose of this work is...
Rolling Contact Mechanics of Graded Coatings Involving Frictional Heating
, Ph.D. Dissertation Sharif University of Technology ; Adibnazari, Saeed (Supervisor) ; Karimzadeh, Ardavan (Co-Supervisor)
Abstract
In this Thesis ,the two-dimensional thermoelastic tractive rolling contact problem for an FGM coated half-plane under the plane strain deformation is investigated. A rigid cylinder rolls on the surface of an FGM coated half-plane with constant translational velocity, generating frictional heat in the slip zones of the contact area. Thermo-mechanical properties of the FGM vary exponentially along the thickness. It is assumed that the contact area consists of a central stick zone and two slip zones of the same sign. The transfer matrix method and Fourier integral transform technique are used to achieve a system of two Cauchy singular integral equations. The associated governing equations are...
Papers on the Political Regimes, Natural Resources, and Economic Institutions
, Ph.D. Dissertation Sharif University of Technology ; Nili, Masoud (Supervisor) ; Barakchian, Mahdi (Supervisor)
Abstract
The formation of development-supporting economic institutions, particularly through the lens of political institutions, remains a central question in political economy. This study distinguishes two key components of political institutions—power distribution and power transition—and empirically demonstrates that power distribution has a significant positive effect on economic institutional quality, while power transition becomes statistically insignificant once power distribution is controlled for. Based on whether political power is centralized or decentralized and whether its transfer is democratic or non-democratic, we define four political regimes: decentralized democracy, centralized...
Political Conflicts, Uncertainty and Investment in Iran
, M.Sc. Thesis Sharif University of Technology ; Barakchian, Mahdi (Supervisor) ; Nili, Masoud (Co-Supervisor)
Abstract
Investment is a variable that would determine the future status of the economy. Given the fact that the investment behavior consequences in the economy would appear in the long-term horizons, unlike most other state variables, such as inflation and exchange rates, it may not be a tangible variable. As a result, there may be fewer sensitivities toward it. However, looking at the evidence, it is observable that the level of investment in Iran has experienced a severe reduction since the early 2010s, and this decline in investment has remained stable in its trend. The real aggregate investment level in Iran at the end of the year 2018 was approximately equal to its level in the year 2002. There...
Design and Implementation of Ultrasound Imaging Structures for Resolution and Frame-Rate Improvement
, Ph.D. Dissertation Sharif University of Technology ; Kavehvash, Zahra (Supervisor) ; Shabani, Mahdi (Supervisor)
Abstract
Ultrasound imaging is one of the most widely used diagnostic methods in medicine due to its safety, low cost, and compact equipment. In conventional ultrasound systems, a two-dimensional image is typically formed through line-by-line scanning, which imposes limitations on both speed and resolution. Plane wave (PW) imaging and synthetic aperture (SA) techniques have been introduced to enhance imaging speed and image quality. However, each of these approaches faces challenges such as limited lateral resolution, hardware complexity, and high computational costs. This dissertation presents two major innovations aimed at improving image quality or reducing system complexity in synthetic aperture...
Innovation of Flexible String and Ball-Spine Inverse Design Methods for 2D and Axisymmentric Internal Flows
, Ph.D. Dissertation Sharif University of Technology ; Hajilouy Benisi, Ali (Supervisor) ; Dor Ali, Mohammad (Supervisor) ; Ghadak, Farhad (Supervisor)
Abstract
Duct Inverse design problems usually involve finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, a novel iterative inverse design method is presented and developed for internal flows. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall’s pressure distribution is reached. The flow field at each step is analyzed to obtain the current pressure distribution along the wall....
The Effect of Political Systems on Economic Performance in Resource-Rich Countries
, M.Sc. Thesis Sharif University of Technology ; Nili, Farhad (Supervisor) ; Nili, Masoud (Co-Advisor)
Abstract
In this research, the effect of political system on economic performance of resource abundant countries is studied. We use political economy litreture to develop a theoritical model in this issue. Here, the politcal systems are divided to democracy and dictatory and in each of them other institutional variable will be introduced. Policy indicator is based on the difference between social welfare in each situation and its optimal amount when maximized. We show that if democracy does not come with high accountability it reduces social welfare more than dictatory. Also, if politician are myopic, democracy aggravates economic performance in those countries. In addition, easy access to income...
Real Effects of Financial Frictions: The Role of Working Capital
, Ph.D. Dissertation Sharif University of Technology ; Nili, Masoud (Supervisor) ; Nili, Farhad (Co-Advisor)
Abstract
Our study investigates the real consequences of variations in the first and second moments of working capital requirement (WCR) in the presence of financial frictions. We introduce a theoretical link from imperfect information about WCR to firms’ performance. Firms choose non-prepaid factors of production with uncertainty about required prepayments, where their access to credit is constrained by collateral. After realization, firms with higher WCR may face financial constraints. This uncertainty influences their demand for inputs, albeit risk-neutrality. Unable to employ the projected level of prepaid input, constrained firms encounter capacity underutilization, leading to misallocation of...