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discrete-phase
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Classification and properties of acyclic discrete phase-type distributions based on geometric and shifted geometric distributions
, Article Journal of Industrial Engineering International ; Volume 15, Issue 4 , 2019 , Pages 651-665 ; 17355702 (ISSN) ; Akhavan Tabatabaei, R ; Salmasi, N ; Modarres, M ; Sharif University of Technology
SpringerOpen
2019
Abstract
Acyclic phase-type distributions form a versatile model, serving as approximations to many probability distributions in various circumstances. They exhibit special properties and characteristics that usually make their applications attractive. Compared to acyclic continuous phase-type (ACPH) distributions, acyclic discrete phase-type (ADPH) distributions and their subclasses (ADPH family) have received less attention in the literature. In this paper, we present the definition, properties, characteristics and PH representations of ADPH distributions and their subclasses with finite state space. Based on the definitions of geometric and shifted geometric distributions, we propose a distinct...
Considering the Environmental Effect on the Performance of Vertical Axis
Wind Turbines (VAWT)
,
M.Sc. Thesis
Sharif University of Technology
;
Sattari, Sorna
(Supervisor)
;
Boroushaki, Mehrdad
(Supervisor)
Abstract
This project aims to investigate environmental effect –such as dust and rain- on the performance of a vertical axis wind turbine (VAWT). However, those issues are frequently investigated in the horizontal axis wind turbines, but this subject has not been studied in vertical axis wind turbines. Impact of rain or dust particles on the turbine blades can change the turbine performance. So consideration of the impact of environmental factors on the performance of wind turbines is very important. Vertical axis wind turbines, particularly the straight bladed VAWT are widely used in wind power generation in agricultural and rural lighting and the use of this type of turbines is increasing...
Investigation of Hydrodynamics of Spouted Beds with Draft Tube Using DPM Approach
, M.Sc. Thesis Sharif University of Technology ; Molaie Dehkordi, Asghar (Supervisor)
Abstract
In this study the spouted bed with draft tube was investigated by discrete phase model for particulate phase and was tried to simulate the spouted bed with high precision by using of experimental data. So, the most accuracy combination of different parameters and sub models was specified. According to this study, the dispersed k-ԑ turbulence model and standard wall function make best prediction. Gidaspow drag model was used for prediction interaction between phases. This study include the effect of Saffman lift force and Rubinow-keller model was chosen for coefficient of Magnus lift force. In Addition, the solid movement pattern was studied in different area of bed especially in fountain...
Numerical Simulation of Particle Classification in Two-Phase Flow in a Vortex-Based Air Classifier Using the Eulerian-Lagrangian Approach and Determining Its Optimized Performance Condition
, M.Sc. Thesis Sharif University of Technology ; Darbandi, Masoud (Supervisor)
Abstract
Using a Numerical simulation approach for modeling multiphase flows is a cost-effective and prevalent method in analyzing the physics of multiphase problems. One of the most applied needs of industry in using gas-particle simulation is the separation of particles using Air Classifiers which are industrial devices that can classify solid inlet particles based on their size using airflow patterns and other mechanisms. The present study focuses on a particular type of classifier using vortex to classify particles. Performance of these classifiers simulated using numerical Eulerian-Lagrangian DDPM model. The two critical studied performance parameters of the classifier are pressure drop and...
Estimating the parameters of mixed shifted negative binomial distributions via an EM algorithm
, Article Scientia Iranica ; Volume 26, Issue 1E , 2019 , Pages 571-586 ; 10263098 (ISSN) ; Akhavan Tabatabaei, R ; Salmasi, N ; Modarres, M ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
Discrete Phase-Type (DPH) distributions have one property that is not shared by Continuous Phase-Type (CPH) distributions, i.e., representing a deterministic value as a DPH random variable. This property distinguishes the application of DPH in stochastic modeling of real-life problems, such as stochastic scheduling, in which service time random variables should be compared with a deadline that is usually a constant value. In this paper, we consider a restricted class of DPH distributions, called Mixed Shifted Negative Binomial (MSNB), and show its flexibility in producing a wide range of variances as well as its adequacy in fitting fat-tailed distributions. These properties render MSNB...
Estimating the parameters of mixed shifted negative binomial distributions via an EM algorithm
, Article Scientia Iranica ; Volume 26, Issue 1E , 2019 , Pages 571-586 ; 10263098 (ISSN) ; Akhavan Tabatabaei, R ; Salmasi, N ; Modarres, M ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
Discrete Phase-Type (DPH) distributions have one property that is not shared by Continuous Phase-Type (CPH) distributions, i.e., representing a deterministic value as a DPH random variable. This property distinguishes the application of DPH in stochastic modeling of real-life problems, such as stochastic scheduling, in which service time random variables should be compared with a deadline that is usually a constant value. In this paper, we consider a restricted class of DPH distributions, called Mixed Shifted Negative Binomial (MSNB), and show its flexibility in producing a wide range of variances as well as its adequacy in fitting fat-tailed distributions. These properties render MSNB...
Numerical Study of Spray Formation in Slinger Injection
, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad (Supervisor)
Abstract
In this M.S. dissertation numerical study of slinger fuel distributer has been studied. This type of atomizer has been used in mini turbojets like Teledyne CAE.
The main purpose of this work was obtaining spray structure of slinger atomizers. This goal was achieved by implementing a UDF code in FLUENT® software to model the primary atomization that include variation of fluid from exit of slinger disk bores till formation of primary droplet. In FLUENT® the DPM method and its ability to utilizing Lagrangian approaches have been used. The result of this model is validated by the data from experimental test that can be found in Articles. This is the first time that spray structure of slinger...
The main purpose of this work was obtaining spray structure of slinger atomizers. This goal was achieved by implementing a UDF code in FLUENT® software to model the primary atomization that include variation of fluid from exit of slinger disk bores till formation of primary droplet. In FLUENT® the DPM method and its ability to utilizing Lagrangian approaches have been used. The result of this model is validated by the data from experimental test that can be found in Articles. This is the first time that spray structure of slinger...
Investigation of the Spray Pattern in the Air Flow Induced by Coaxial Rotors Used for Pesticide Spraying
, M.Sc. Thesis Sharif University of Technology ; Morad, Mohammad Reza (Supervisor) ; Hejranfar, Kazem (Supervisor)
Abstract
The production of agricultural products is one of the most important human economic activities. The issue of mechanized and optimal use of pesticides is vital for human health and the environment, and the use of helicopters makes this possible. Although spray-based systems in helicopters are one of the most effective ways to produce agricultural products, it is still unclear how droplet movement in aerial spraying is affected by the complex downwash flow created by rotors. Modeling agricultural air spray to identify the spray trend of droplets in the air stream, downwash flows, and consequent vortices has attracted more attention as a result of the development of computational fluid...
Two-phase flow separation in axial free vortex flow
, Article Journal of Computational Multiphase Flows ; Volume 9, Issue 3 , 2017 , Pages 105-113 ; 1757482X (ISSN) ; Ganjiazad, R ; Roshandel, R ; Ashjari, M. A ; Sharif University of Technology
Abstract
Multi-phase flows, particularly two-phase flows, are widely used in the industries, hence in order to predict flow regime, pressure drop, heat transfer, and phase change, two-phase flows should be studied more precisely. In the petroleum industry, separation of phases such as water from petroleum is done using rotational flow and vortices; thus, the evolution of the vortex in two-phase flow should be considered. One method of separation requires the flow to enter a long tube in a free vortex. Investigating this requires sufficient knowledge of free vortex flow in a tube. The present study examined the evolution of tube-constrained two-phase free vortex using computational fluid dynamics. The...
Phase-type Distribution in the Sequencing and Scheduling Problem and its Application in Operating Room Problem
, Ph.D. Dissertation Sharif University of Technology ; Salmasi, Nasser (Supervisor) ; Modarres, Mohammad (Supervisor)
Abstract
Operating rooms (ORs) are considered as the most valuable resource in hospital, which are the largest revenue generator and, at the same time, the largest cost center of hospitals. Hospital managers have been interested in improving the efficiency and effectiveness of ORs by developing modern planning and scheduling tools. This research studies the stochastic operating room (OR) scheduling problem integrated by Post-Anesthesia Care Unit (PACU), named the operating theater room (OTR) problem. Due to the inherent uncertainty in surgery duration and its consecutive PACU time, the completion time of the operation of a patient should be modeled as the sum of a number of random variables. Several...
CFD Modeling of Ammonia Release and Water Curtain for Mitigation
,
M.Sc. Thesis
Sharif University of Technology
;
Rashtchian, Davoud
(Supervisor)
Abstract
The release of toxic materials causes tragic accidents every year. There are various techniques in order to mitigate the release effect of these materials such as Application of air jets, steam curtains and water curtains. This study presents numerical calculations to reproduce the continuous ammonia release dispersion with and without the mitigating influence of a downwind water curtain using computational fluid dynamic (CFD) software ANSYS Fluent 15.0. The RNG model coupled with Lagrangian discrete phase model (DPM) was used to simulate the dilution effectiveness of the water curtain system. The ammonia absorption was taken into account by means of user-defined functions (UDF). The...
Three Dimensional Numerical Simulation of Slinger Combustor
, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad (Supervisor)
Abstract
Annular combustion chambers used in small turbine motors which incorporate centrifugal (rotary) injectors for injecting fuel, are known as Slinger combustion chambers. The Slinger injector works in such a way that fuel enters from an inner tube in motor shaft and exits with high pressure from the holes on the cylinder connected to the shaft. Because of the high centrifugal force, the fuel is sprayed with high quality after entering the combustion chamber. Type and angle of spray, fuel-air mixing type, combustion phenomena and flame stability makes this different than other annular combustion chambers. The process of combustion in the Slinger chamber of YJ402 motor is numerically simulated in...
Design and analysis of a cooling system for a supersonic exhaust diffuser
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 233, Issue 14 , 2019 , Pages 5253-5263 ; 09544100 (ISSN) ; Fouladi, N ; Mirbabaei, A. R ; Sharif University of Technology
SAGE Publications Ltd
2019
Abstract
High-altitude test facilities are usually used to evaluate the performance of space mission engines. The supersonic exhaust diffuser, a main part of high-altitude test facility, provides the required test cell vacuum conditions by self-pumping the nozzle exhaust gases to the atmosphere. However, the plume temperature is often much higher than the temperature the diffuser structure is able to withstand, usually above 2500 K. In this study, an efficient cooling system is designed and analyzed to resolve the thermal problem. A water spray cooling technique is preferred among various existing techniques. Here, a new algorithm is developed for a spray cooling system for a supersonic exhaust...