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    Separation control of aero boundary layer in supercavitating bodies and its effect on pressure drag reduction

    , Article 2005 ASME Fluids Engineering Division Summer Conference, Houston, TX, 19 June 2005 through 23 June 2005 ; Volume 1 PART A , 2005 , Pages 731-739 ; 0791841987 (ISBN); 9780791841983 (ISBN) Khakpour, Y ; Yazdani, M ; Sharif University of Technology
    2005
    Abstract
    Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. In fact such methodologies consider cavitation flow statically, rather than taking dynamic effects of overall flow into account. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Thereby, in order to configure the system conditions which may be cause of cavity perturbation and so system oscillation, we need to use proper methodologies in which... 

    On the stability of supercavitating projectiles based on lagrangian analysis

    , Article 2005 ASME Fluids Engineering Division Summer Conference, Houston, TX, 19 June 2005 through 23 June 2005 ; Volume 1 PART A , 2005 , Pages 741-749 ; 0791841987 (ISBN); 9780791841983 (ISBN) Khakpour, Y ; Yazdani, M ; Sharif University of Technology
    2005
    Abstract
    In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating Shkval missile. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile's motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is... 

    Separation control of aero boundary layer in supercavitating bodies and its effect on pressure drag reduction

    , Article 2005 ASME Fluids Engineering Division Summer Meeting, FEDSM2005, Houston, TX, 19 June 2005 through 23 June 2005 ; Volume 2005 , 2005 , Pages 19-27 ; 0791837602 (ISBN); 9780791837603 (ISBN) Khakpour, Y ; Yazdani, M ; Sharif University of Technology
    2005
    Abstract
    Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. In fact such methodologies consider cavitation flow statically, rather than taking dynamic effects of overall flow into account. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Thereby, in order to configure the system conditions which may be cause of cavity perturbation and so system oscillation, we need to use proper methodologies in which... 

    On the stability of supercavitating projectiles based on lagrangian analysis

    , Article 2005 ASME Fluids Engineering Division Summer Meeting, FEDSM2005, Houston, TX, 19 June 2005 through 23 June 2005 ; Volume 2005 , 2005 , Pages 29-37 ; 0791837602 (ISBN); 9780791837603 (ISBN) Khakpour, Y ; Yazdani, M ; Sharif University of Technology
    2005
    Abstract
    In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating Shkval missile. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile's motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is... 

    On the effects of aero boundary layer control on pressure drag reduction in supercavitating bodies

    , Article 24th International Conference on Offshore Mechanics and Arctic Engineering, 2005, Halkidiki, 12 June 2005 through 17 June 2005 ; Volume 2 , 2005 , Pages 665-675 Khakpour, Y ; Yazdani, M ; Sharif University of Technology
    2005
    Abstract
    Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Furthermore as we'll see, pressure distribution on cavity surface caused due to overall conditions, induct nonaxisymetric forces and they may need to be investigated. Primarily we describe how pressure distribution into the cavity can cause separation of the aero boundary layer. Then we present... 

    Stability enhancement of supercavitating projectiles by unsteady air injection

    , Article 24th International Conference on Offshore Mechanics and Arctic Engineering, 2005, Halkidiki, 12 June 2005 through 17 June 2005 ; Volume 2 , 2005 , Pages 457-466 Khakpour, Y ; Yazdani, M ; Sharif University of Technology
    2005
    Abstract
    In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating hydrofoils.Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile's motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is... 

    Assessment of Caspian Gas Transit and its Effects on the Interests of the Iranian Desired

    , M.Sc. Thesis Sharif University of Technology Khakpour, Hossein (Author) ; Maleki, Abbas (Supervisor)
    Abstract
    In this project a model for the analysis and assessment of gas transit in the Caspian Sea and its effects on the desired benefits of the approach of decision-making, has been developed.
    The first comprehensive review of the supply and demand of gas in the world and the countries of the Caspian region and the cast has been affecting world energy developments.After a comprehensive analysis of the status of the gas transit routes from the Caspian region and provided. Then, using the Delphi method and elite views the main criteria related to gas transit and affecting the interests of the countries of the Caspian region to determine the detailed criteria for each main criterion was determined... 

    Determination of Forming Limit Diagram with Existence of Normal Stress and Investigation on the Methods of Calibration in this Diagram

    , M.Sc. Thesis Sharif University of Technology Khakpour Nejad Khaki, Hamid (Author) ; Assempour, Ahmad (Supervisor)
    Abstract
    Theoretical studies in the analysis of sheet metal failures are referred to obtain the Forming Limit Diagrams (FLDs). Since extracting the Forming Limit Diagrams experimentally is cost and time consuming, many researches have been accomplished for obtaining these diagrams theoretically. However, in many of these researches, the assumption of plane stress state has been used to obtain the FLD, which is not correct in some processes such as hydroforming because of high level of normal stress. In this study, determination of the forming limit diagram with existence of the normal stress is based on the Marciniak and Kuczynski model. Newton-Raphson method has been used to find the set of... 

    Forming limit diagram of tubular hydroformed parts considering the through-thickness compressive normal stress

    , Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 230, Issue 1 , 2016 , Pages 332-343 ; 14644207 (ISSN) Hashemi, R ; Abri Nia, K ; Assem Pour, A ; Khakpour Nejadkhaki, H ; Shahbazi Mastan Abad, A ; Sharif University of Technology
    SAGE Publications Ltd  2016
    Abstract
    In this study, the effect of a compressive normal stress has been considered in the determination of forming limit diagrams and forming limit stress diagrams to predict neck initiation failure in tube hydroforming of T-shaped parts. Computation of the forming limit diagrams and FLSDs is based on the generalized Marciniak and Kuczynski method to consider the existence of through-thickness compressive normal stress. The proposed forming limit diagrams and FLSDs were used in conjunction with ABAQUS/EXPLICIT finite element simulations to predict the onset of necking in tube hydroforming of T-shaped part. The amount of calibration pressure and axial feeding required to produce an acceptable part... 

    Coordinated actor model of self-adaptive track-based traffic control systems

    , Article Journal of Systems and Software ; Volume 143 , 2018 , Pages 116-139 ; 01641212 (ISSN) Bagheri, M ; Sirjani, M ; Khamespanah, E ; Khakpour, N ; Akkaya, I ; Movaghar, A ; Lee, E. A ; Sharif University of Technology
    Elsevier Inc  2018
    Abstract
    Self-adaptation is a well-known technique to handle growing complexities of software systems, where a system autonomously adapts itself in response to changes in a dynamic and unpredictable environment. With the increasing need for developing self-adaptive systems, providing a model and an implementation platform to facilitate integration of adaptation mechanisms into the systems and assuring their safety and quality is crucial. In this paper, we target Track-based Traffic Control Systems (TTCSs) in which the traffic flows through pre-specified sub-tracks and is coordinated by a traffic controller. We introduce a coordinated actor model to design self-adaptive TTCSs and provide a general... 

    Coordinated actors for reliable self-adaptive systems

    , Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 19 October 2016 through 21 October 2016 ; Volume 10231 LNCS , 2017 , Pages 241-259 ; 03029743 (ISSN) ; 9783319576657 (ISBN) Bagheri, M ; Akkaya, I ; Khamespanah, E ; Khakpour, N ; Sirjani, M ; Movaghar, A ; Lee, E. A ; Khosravi, R ; Kouchnarenko, O ; Sharif University of Technology
    2017
    Abstract
    Self-adaptive systems are systems that automatically adapt in response to environmental and internal changes, such as possible failures and variations in resource availability. Such systems are often realized by a MAPE-K feedback loop, where Monitor, Analyze, Plan and Execute components have access to a runtime model of the system and environment which is kept in the Knowledge component. In order to provide guarantees on the correctness of a self-adaptive system at runtime, the MAPE-K feedback loop needs to be extended with assurance techniques. To address this issue, we propose a coordinated actor-based approach to build a reusable and scalable model@runtime for self-adaptive systems in the... 

    Calculation of the Energy Release Rate of Nano-Cracks in FCC Materials Via the Many Body Atomic Scale FEM

    , M.Sc. Thesis Sharif University of Technology Ostad Hossein, Alireza (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    Abstract
    Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

    Semisolid Stir Joining of As-Cast Silicon-Aluminum Bronze

    , M.Sc. Thesis Sharif University of Technology Ferasat, Keyvan (Author) ; Kokabi, Amir Hossein (Supervisor) ; Ashuri, Hossein (Supervisor)
    Abstract
    Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

    The Study of Eliminating Gender Gap in Iran Labor Market on Participation Rate of Married Urban Women

    , M.Sc. Thesis Sharif University of Technology Asghari, Fatemeh (Author) ; Rahmati, Mohammad Hossein (Supervisor) ; Joshaghani, Hossein (Supervisor)
    Abstract
    The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's... 

    Graph homomorphisms through random walks [electronic resource]

    , Article Journal of Graph Theory ; 2003, Volume 44, Issue 1, pages 15–38 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    In this paper we introduce some general necessary conditions for the existence of graph homomorphisms, which hold in both directed and undirected cases. Our method is a combination of Diaconis and Saloff–Coste comparison technique for Markov chains and a generalization of Haemers interlacing theorem. As some applications, we obtain a necessary condition for the spanning subgraph problem, which also provides a generalization of a theorem of Mohar (1992) as a necessary condition for Hamiltonicity. In particular, in the case that the range is a Cayley graph or an edge-transitive graph, we obtain theorems with a corollary about the existence of homomorphisms to cycles. This, specially, provides... 

    Unique list-colourability and the fixing chromatic number of graphs [electronic resource]

    , Article Discrete Applied Mathematics ; Volume 152, Issues 1–3, 1 November 2005, Pages 123–138 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    In this paper we introduce a chromatic parameter, called the fixing chromatic number, which is related to unique colourability of graphs, in the sense that it measures how one can embed the given graph G in G∪Kt by adding edges between G and Kt to make the whole graph uniquely t-colourable. We study some basic properties of this parameter as well as its relationships to some other well-known chromatic numbers as the acyclic chromatic number. We compute the fixing chromatic number of some graph products by applying a modified version of the exponential graph construction  

    Circular colouring and algebraic no-homomorphism theorems

    , Article European Journal of Combinatorics ; Volume 28, Issue 6, August 2007, Pages 1843–1853 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    In this paper, we apply some new algebraic no-homomorphism theorems in conjunction with some new chromatic parameters to estimate the circular chromatic number of graphs. To show the applicability of the general results, as a couple of examples, we generalize a well known inequality for the fractional chromatic number of graphs and we also show that the circular chromatic number of the graph obtained from the Petersen graph by excluding one vertex is equal to 3. Also, we focus on the Johnson–Holroyd–Stahl conjecture about the circular chromatic number of Kneser graphs and we propose an approach to this conjecture. In this regard, we introduce a new related conjecture on Kneser graphs and we... 

    Density and power graphs in graph homomorphism problem

    , Article Discrete Mathematics ; Volume 308, Issue 17, 6 September 2008, Pages 4027–4030 Daneshgar, A. (Amir) ; Hajiabolhassan, Hossein ; Sharif University of Technology
    Abstract
    We introduce two necessary conditions for the existence of graph homomorphisms based on the concepts of density and power graph. As corollaries, we obtain a lower bound for the fractional chromatic number, and we set forward elementary proofs of the facts that the circular chromatic number of the Petersen graph is equal to three and the fact that the Coxeter graph is a core  

    Temperature dependence study of nonocontact AFM images using molecular dynamics simulations [electronic resource]

    , Article Int. Journal of Modern Physics ; 2012, Vol. 5, pp. 418-432 Nejat Pishkenari, H. (Hossein) ; Meghdar, Ali ; Sharif University of Technology
    Abstract
    The effect of temperature on the noncontact atomic force microscopy (NC-AFM) surface imaging is investigated with the aid of molecular dynamics (MD) analysis based on the Sutton-Chen (SC) interatomic potential. Particular attention is devoted to the tip and sample flexibility at different temperatures. When a gold coated probe is brought close to the Au (001) surface at high temperatures, the tip and surface atoms are pulled together and their distance becomes smaller. The tip and sample atoms displacement varies in the different environment temperatures and this leads to the different interaction forces. Along this line, to study the effect of temperature on the resulting images, we have... 

    Developing an Analytical Model for Predicting the Residual Stresses Induced by Shot Peening with Considering the Effect of Initial Surface Treatment

    , Ph.D. Dissertation Sharif University of Technology Sherafatnia, Khalil (Author) ; Farrahi, Gholam Hossein (Supervisor) ; Mahmoudi, Amir Hossein (Co-Supervisor)
    Abstract
    Shot peening is a cold-working process commonly used in industry to improve the fatigue performance, stress corrosion resistance and surface nano-crystallization of metallic parts. This process extends fatigue life via two mechanisms: Preventing the crack growth due to compressive residual stresses and, preventing the crack initiation because of increased material hardness. These mechanisms are the results of the bombardment of the component's surface with small spherical particles. In this research, an analytical model is developed for estimating the residual stress distribution induced by shot peening process. The modifications of the developed analytical model are related to...