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Modeling of Liquid-Vapor Two Phase Flow through Nozzle
, M.Sc. Thesis Sharif University of Technology ; Nouri Borujerdi, Ali (Supervisor)
Abstract
This thesis is about modeling of liquid-vapor two phase flows through nozzle. Liquid-vapor two phase flow is very applicable in industries such as boilers, expansion valves, refrigeration and sudden failures in pipelines. Two models are used for modeling of fluid flow through nozzle, transient and steady state. In Both model the solution field is considered as saturated liquid and vapor and the mass, momentum and energy equations as well as equation of state is used for describing of fluid flow properties. Homogeneous equilibrium model is used and for complete modeling of fluid flow heat transfer and friction force is also considered.
Numerical solutions are used for solving of the...
Numerical solutions are used for solving of the...
Level Set Approach for Capturing Interface Position of Annular Two-Phaseflow
, M.Sc. Thesis Sharif University of Technology ; Nouri-Borujerdi, Ali (Supervisor)
Abstract
Numerical simulation of air-water annular two-phase flow in a tube is carried out by using level set method for determining position of interface between two phases. Governing equations include continuity, momentum and level set equations that considered for each phase. The finite difference scheme is used to discretize the differential equations. The SIMPLE algorithm is adopted to solve the discretized equations for linking continuity and momentum equation. An unequally spaced staggered grid size for flow field is adopted. The Level Set method is used to capture interface position between two phases. To increase the accuracy of solution at level set equation, 5th order finite difference and...
Numerical Simulation of Reacting Flow with Chemical Kinetics using a Modified Dual-Algorithm
, Ph.D. Dissertation Sharif University of Technology ; Darbandi, Masoud (Supervisor) ; Ghafourian, Akbar ($item.subfieldsMap.e)
Abstract
An important issue in aerospace propulsion systems is the reacting flow analyses, which involve many different concepts and physics including various chemical reactions mechanisms and radiation and convection heat transfer physics. As known, the computer simulation is a powerful tool to analyze the reacting flow physics in various combusting environments. It can suitably provide details of both chemical reaction occurrences and heat transfer physics. In combustion environments, the temperature gradient is noticeably affected by the density gradient. On the other hand, the accurate modeling of density gradients highly affects the computational results. In practice, the density-based methods...
Computational analysis of nanofluid effects on convective heat transfer enhancement of micro-pin-fin heat sinks
, Article International Journal of Thermal Sciences ; Volume 58 , 2012 , Pages 168-179 ; 12900729 (ISSN) ; Feizbakhshi, M ; Sharif University of Technology
Elsevier
2012
Abstract
Numerical investigation on the application of nanofluids in Micro-Pin-Fin Heat Sinks (MPFHSs) has been presented in this paper. To investigate flow and heat transfer behavior in MPFHS the three-dimensional steady Navier-Stokes and energy equations were discretized using a finite volume approach and have been solved iteratively, using the SIMPLE algorithm. DI-water is used as a base coolant fluid while the nanoparticles used in the present study are CuO nanoparticles with mean diameters of 28.6 and 29 nm and Al 2O 3 nanoparticles with mean diameters of 38.4 and 47 nm. The results show that (i) a significant enhancement of heat transfer in the MPFHS due to suspension of CuO orAl 2O 3...
Simple and efficient remote sensing image transformation for lossless compression
, Article Proceedings of SPIE - The International Society for Optical Engineering ; Volume 8285 , 2011 ; 0277786X (ISSN) ; 9780819489326 (ISBN) ; Ghamisi, P ; Mortazavi, M ; Choupan, J ; Sharif University of Technology
2011
Abstract
Remote Sensing (RS) images or satellite images include information about earth. Compression of RS images is important in the field of satellite transmission systems and mass storage purposes. Because of importance of information and existent of large amount of details, lossless compression preferred. Real time compression technique is applied on satellite and aerial transmission systems [1]. A simple algorithm accelerates the whole process in real time purposes. Lossless JPEG, JPEG-LS and JPEG2000 are some famous lossless compression methods. Transformation is the first step of these methods. In this paper, a simple and efficient method of lossless image transformation has been introduced by...
Optimal rate and delay performance in non-cooperative opportunistic spectrum access
, Article Proceedings of the International Symposium on Wireless Communication Systems, 28 August 2012 through 31 August 2012 ; August , 2012 , Pages 56-60 ; 21540217 (ISSN) ; 9781467307604 (ISBN) ; Khodaian, M ; Sharif University of Technology
2012
Abstract
We study transmission rate control and performance delay in cognitive radio (CR) links from a cross-layer perspective. We assume a hierarchical CR network where the secondary users (SU) access the spectrum band in an opportunistic and noncooperative way. The SU goal is to transmit a fixed-size file (fixed amount of data packets) during the sojourn time of the primary users (PU's) idle state. We assume that the SU's support frames retransmission through an automatic repeat request (ARQ) mechanism. By formulating the problem as a Markov decision process, we demonstrate that there is always an optimal stationary rate adaptation policy, and we propose a simple algorithm to obtain it. We derive...
A novel OCR system for calculating handwritten persian arithmetic expressions
, Article IEEE International Symposium on Signal Processing and Information Technology, ISSPIT 2009, 14 December 2009 through 16 December 2009 ; 2009 , Pages 277-282 ; 9781424459506 (ISBN) ; Tirdad, P ; Rabiee, H. R ; Parviz, M ; Sharif University of Technology
Abstract
In this paper we propose a novel OCR system which can recognize and calculate handwritten Persian arithmetic expressions without using a keyboard or a memory to store the intermediate results. Our research is composed of two major phases: character recognition and calculation. The recognition phase is based on a new approach for feature extraction. Fuzzy Support Vector Machines (FSVMs) are employed as the classifier. In calculation phase a simple algorithm is used for calculating the recognized arithmetic expression. The performance of the system is evaluated on a database consisting of 3400 digits and symbols written by 20 different people. 92 percent accuracy in recognition proves the good...
A novel OCR system for calculating handwritten Persian arithmetic expressions
, Article 8th International Conference on Machine Learning and Applications, ICMLA 2009, 13 December 2009 through 15 December 2009 ; 2009 , Pages 755-758 ; 9780769539263 (ISBN) ; Tirdad, P ; Rabiee, H. R ; Parviz, M ; Sharif University of Technology
Abstract
In this paper, we propose a novel OCR system which can recognize and calculate handwritten Persian arithmetic expressions without using a keyboard or a memory to store the intermediate results. Our system is composed of two major phases: character recognition and calculation. The recognition phase is based on a new approach for feature extraction followed by a Fuzzy Support Vector Machines (FSVMs) as the classifier. In calculation phase a simple algorithm is used for calculating the recognized arithmetic expressions. The performance of the system was evaluated on a database consisting of 3400 digits and symbols written by 20 different people. 92 percent accuracy in recognition proves the...
Effect of traffic-load dependent vehicle routing algorithm on the connectivity in VANETs
, Article IEEE Vehicular Technology Conference, 15 May 2011 through 18 May 2011 ; May , 2011 , Page(s): 1 - 5 ; 15502252 (ISSN) ; 9781424483310 (ISBN) ; Ashtiani, F ; Sharif University of Technology
2011
Abstract
In this paper, we evaluate how traffic-load dependent vehicle routing at intersections is able to improve the connectivity status of all streets. To this end, we consider a VANET scenario, comprised of several streets and intersections. Then, we focus on two vehicle routing algorithms, one based on the distance to destination, i.e., traffic-load independent (TLI) algorithm, and another one based on both distance to destination and traffic load status of the local streets, i.e., traffic-load dependent (TLD) algorithm. By employing a simple mobility model based on an open BCMP queueing network, we derive the spatial traffic distribution at two cases. Afterwards, we propose a simple algorithm...
A simple consensus algorithm for distributed averaging in random geographical networks
, Article Pramana - Journal of Physics ; Volume 79, Issue 3 , August , 2012 , Pages 493-499 ; 03044289 (ISSN) ; Sharif University of Technology
2012
Abstract
Random geographical networks are realistic models for wireless sensor networks which are used in many applications. Achieving average consensus is very important in sensor networks and the faster the consensus is, the durable the sensors' life, and thus, the better the performance of the network. In this paper we compared the performance of a number of linear consensus algorithms with application to distributed averaging in random geographical networks. Interestingly, the simplest algorithm - where only the degree of receiving nodes is needed for the averaging - had the best performance in terms of the consensus time. Furthermore, we proved that the network has guaranteed convergence with...
Control of thermo magnetic heat transfer in porous cavity with Baffle(s)
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 9, Issue PART A , 2010 , Pages 627-631 ; 9780791843826 (ISBN) ; Davoudi, M ; Pirmohammadi, M ; Sharif University of Technology
Abstract
Steady, laminar, natural-convection flow in the presence of a magnetic field in a porous cavity heated from left wall sinusoidally and cooled from right wall is considered. It is well known that unavoidable hydrodynamic movements can be damped with the help of a magnetic field. The Finite Volume method and SIMPLE algorithm for discretizing is used to solve the non-dimensional governing equations. The Convection and Diffusion term of the equations are discretized by Central Difference Scheme (CDS).The numerical procedure has been done over a range of Rayleigh number, Ra, and value of Hartmann number (Ha), 0 ≤ Ha ≤ 150 and effect of them is investigated on average and local Nusselt number....
Investigation of the effect of adding nano-encapsulated phase change material to water in natural convection inside a rectangular cavity
, Article Journal of Energy Storage ; Volume 40 , 2021 ; 2352152X (ISSN) ; Goudarzi, S ; Kazemi Varnamkhasti, H ; Amigh, H ; Ghaemi, F ; Baleanu, D ; Karimipour, A ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The present simulation aims to investigate adding NEPCM nanoparticles to water in the natural convection inside a cavity by using FVM method and SIMPLE algorithm. Nano-encapsulated phase change material (NEPCM) consists of a shell and core with phase change property. The NEPCM particles in base fluid have the ability to transfer heat by absorbing and dissipating heat in the liquid-solid phase change state. In this study, the energy wall phenomenon due to the phase change of NEPCM core has appeared that the whose energy transfer strength is proportional to the latent heat of NEPCM core and the thickness of the energy wall. Moreover, the relationship between the energy wall and the heat...
Compound triple jets film cooling improvements via velocity and density ratios: Large eddy simulation
, Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 133, Issue 3 , Mar , 2011 ; 00982202 (ISSN) ; Ramezanizadeh, M ; Taeibi Rahni, M ; Salimi, M ; Sharif University of Technology
2011
Abstract
The flow hydrodynamic effects and film cooling effectiveness placing two small coolant ports just upstream the main jet (combined triple jets) were numerically investigated. Cross sections of all jets are rectangular and they are inclined normally into the hot cross-flow. The finite volume method and the SIMPLE algorithm on a multiblock nonuniform staggered grid were applied. The large-eddy simulation approach with three different subgrid scale models was used. The obtained results showed that this flow configuration reduces the mixing between the freestream and the coolant jets and hence provides considerable improvements in film cooling effectiveness (both centerline and spanwise averaged...
Unsteady multiphase modeling of cavitation around NACA 0015
, Article Journal of Marine Science and Technology ; Volume 18, Issue 5 , 2010 , Pages 689-696 ; 10232796 (ISSN) ; Jahanbakhsh, E ; Seif, M. S ; Sharif University of Technology
Abstract
The present study focuses on the numerical simulation of cavitation around the NACA 0015. The unsteady behaviors of cavitation which have worthwhile applications are investigated. The cavitation patterns, velocity fields and frequency of the cavitating flow around hydrofoil is obtained. For multi phase simulation, single-fluid Navier-Stokes equations, along with a volume fraction transport equation, are employed. The bubble dynamics model is utilized to simulate phase change. SIMPLE algorithm is used for velocity and pressure computations. For discretization of equations the finite-volume approach written in body fitted curvilinear coordinates, on collocated grid, is used. In this study,...
Low-rank matrix approximation using point-wise operators
, Article IEEE Transactions on Information Theory ; Volume 58, Issue 1 , September , 2012 , Pages 302-310 ; 00189448 (ISSN) ; Karbasi, A ; Marvasti, F ; Sharif University of Technology
Abstract
The problem of extracting low-dimensional structure from high-dimensional data arises in many applications such as machine learning, statistical pattern recognition, wireless sensor networks, and data compression. If the data is restricted to a lower dimensional subspace, then simple algorithms using linear projections can find the subspace and consequently estimate its dimensionality. However, if the data lies on a low-dimensional but nonlinear space (e.g., manifolds), then its structure may be highly nonlinear and, hence, linear methods are doomed to fail. In this paper, we introduce a new technique for dimensionality reduction based on point-wise operators. More precisely, let $ {bf A} n...
Improvements on the k-center problem for uncertain data extended abstract
, Article Proceedings of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems ; 27 May , 2018 , Pages 425-433 ; 9781450347068 (ISBN) ; Jafari, A ; Sharif University of Technology
Association for Computing Machinery
2018
Abstract
In real applications, there are situations where we need to model some problems based on uncertain data. This leads us to define an uncertain model for some classical geometric optimization problems and propose algorithms to solve them. The assigned version of the k-center problem for n uncertain points in a metric space is studied in this paper. The main approach is to replace each uncertain point with a clever choice of a certain point. We argue that the k-center solution for these certain replacements of our uncertain points, is a good constant approximation factor for the original uncertain k-center problem. This approach enables us to present fast and simple algorithms that give...
Effective partitioning of input domains for ALM algorithm
, Article 1st Iranian Conference on Pattern Recognition and Image Analysis ; 2013 ; 9781467362047 (ISBN) ; Ghaffari, A ; Shouraki, S. B ; Sharif University of Technology
2013
Abstract
This paper presents a new and simple algorithm for partitioning the input domain for implementation of Active Learning Method (ALM) algorithm. ALM is a pattern-based algorithm for soft computing which uses the Ink Drop Spread (IDS) algorithm as its main engine for feature extraction. In this paper a simple algorithm is introduced with a few computation cost. In order to evaluate the performance of the proposed algorithm, it is applied to two applications, system modeling and pattern recognition. Simulation results show the effectiveness of our algorithm in specifying the appropriate points for dividing the inputs domains
Online conflict-free coloring of intervals
, Article Scientia Iranica ; Vol. 21, issue. 6 , 2014 , p. 2138-2141 ; Seraji, M. J. R ; Shadravan, M ; Sharif University of Technology
Abstract
In this paper, we study the problem of online conflict-free coloring of intervals on a line, where each newly inserted interval must be assigned a color upon insertion such that the coloring remains conflict-free, i.e. for each point p in the union of the current intervals, there must be an interval I with a unique color among all intervals covering p. We first present a simple algorithm which uses O(√n) colors where n is the number of current intervals. Next, we propose an CF-coloring of intervals which uses O(log3 n) colors
On the power of the semi-separated pair decomposition
, Article Computational Geometry: Theory and Applications ; Volume 46, Issue 6 , 2013 , Pages 631-639 ; 09257721 (ISSN) ; Carmi, P ; Farshi, M ; Smid, M ; Sharif University of Technology
2013
Abstract
A Semi-Separated Pair Decomposition (SSPD), with parameter s>1, of a set SâŠ"Rd is a set {(Ai,Bi)} of pairs of subsets of S such that for each i, there are balls DAi and DBi containing Ai and Bi respectively such that d(DAi,DBi)≥s×min(radius(DAi), radius(DBi)), and for any two points p,qâ̂̂S there is a unique index i such that pâ̂̂Ai and qâ̂̂Bi or vice versa. In this paper, we use the SSPD to obtain the following results: First, we consider the construction of geometric t-spanners in the context of imprecise points and we prove that any set SâŠ"Rd of n imprecise points, modeled as pairwise disjoint balls, admits a t-spanner with O(nlogn/(t-1)d) edges that can be computed in O(nlogn/(t-1)d)...