Sharif Digital Repository

The scarcity of potable water is one of the world's challenges. In the Middle East, this crisis is even worse and as a consequence, the most aggregation of desalination plants has been constructed in this area. However, brine effluent discharged from these plants entails serious environmental issues. Despite the extensive studies about the investigation of dilution and the area which faces the brine discharges as submerge jets, there are a few experimental investigations with a focus on the injecting brine discharge into the shallow environment. Whereas the Persian Gulf's coastal environment is shallow. Moreover, there is a huge construction of desalination held in this area. Accordingly,... 

Light has planar wavefront as it propagates in vacuum but in the atmosphere, because it passes through layers with different refractive indices, this planar wavefront is lost. Consequently light is distorted when it enters optical instruments. This issue results in images with low resolution. Adaptive optics is a method used for compensation of these distortions in order to obtain higher resolution. So far adaptive optics systems are successfully used in ground based telescopes and an increasing effort on developing and improving these systems is made. Most of these studies are performed from the optics point of view, but techniques from control theory can be applied to adaptive optics... 

Present research focuses on providing a reasonable solution for separation control through arrays of discrete wall jets. In this thesis, quasi-radial wall jet actuators have been introduced and theirs application in separation control (boundary layer control) have been investigated for the first time. This study includes two phases. The first phase is dedicated to investigation of physics and functional nature of wall jet actuators. In this phase, using numerical simulations, wall jet actuators in different situations have been studied and it was shown that arrays of quasi-radial jets have better performance than arrays of three-dimensional jets in creating a combine two-dimensional wall... 

Marketing innovation is an idea that is the focal point of numerous marketing scholars recently. This study investigated relationships among the innovation ambidexterity, marketing innovation, marketing agility, and the moderator effect of market turbulence. Attempts are made to understand ambidexterity and agility notions from marketing perspectives to accelerate marketing innovation and identify measures for all of the mentioned constructs. Main theories which have been used to justify the constructs’ relationships are dynamic capability point of view, resource-based theory, and ambidexterity theory. Structural equation modeling (SEM), utilizing the technique of partial least squares... 

Stock exchanges are one of the most important capital markets and let people and institutions to insvest their savings in stocks and therefore earn money. Investors are going to select a portfolio that has the maximum return and minimum risk; so, they try to forecast stock returns and volatilities. Predictability of stock return and volatility is also important for asset pricing and investigating market efficiency. Now, the question is “are stock returns and volatilities predictable using historical returns and volatilities?” In this research, return and volatility predictability of Tehran Stock Exchange indexes by using historical data are investigated. First, the outocorrelation of return... 

In this research special type of jets those calls Arc-Shape Jets are studied. The meaning of this research is an effort to introduce this types of jets as a new method to film-cooling approach. In the primary section, the fitness of this scheme on a flat plate is studied. After this section, according to the results, this method is implemented on a turbine blade surface. According to the results, this method of film-cooling has suitable effectiveness in lateral direction, this has a reason of radially injection of the coolant jet. The main feature of this concept is operating by mass flow rate of much lower than other schemes. So that in a regular injection of a 45 degrees of actuator arc,... 

We study the Navier-Stokes equations with an extra Eddy viscosity term in the whole space . We introduce a suitable regularized system for which we prove the existence of a regular solution defined for all time. We prove that when the regularizing parameter goes to zero, the solution of the regularized system converges to a turbulent solution of the initial system. In the first chapter, we have dedicated the necessary preliminaries and then in the second chapter, we have introduced the types of solutions. The third chapter introduces the necessary tools and their properties, with the help of which in the next chapter we have been able to make estimates and obtain their extensions to prove... 

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... 

In order to improve performance and optimize design of high pressure combustion devices such as liquid rocket engine, gas turbine engine, and diesel engine there is a need for comprehensive understanding of injection, mixing and combustion in supercritical condition. Under this condition chamber pressure is higher than critical pressure of fuel and oxidizer. The characteristic of supercritical condition, include changing thermophysical properties such as density, CP, and compressibility factor. Therefore under this condition ideal state equation cannot correctly predict the mentioned properties. These characteristics make supercritical combustion different from other combustion regimes.... 

MILD combustion under high preheating and high dilution condition illustrates some interesting characteristics. Very low oxygen concentration in the reaction zone and reduced chemical reaction rates compared to conventional combustion are some of these features which make MILD combustion to be an unique type of combustion. In this work numerical investigation of a gas turbine model combustor (GTMC) was aimed to done using model of the EDC as turbulence-chemistry interaction combustion model. Modeling was performed by solving RANS equations and RSM equations for a 2D axisymmetric computational domain. The combustion chamber was investigated for both reacting and non-reacting conditions. A... 

In this thesis numerical investigation on the effect of injecting plasma into the MILD combustion regime which is based on the low oxygen dilution and high preheated temperature, were carried out. The burner which was utilized in this study is a co-flow burner, consists of three coaxial channels. From the center to the outside, there is a fuel jet at the center part, a co-flowing dielectric barrier discharge (DBD), and a preheated air section that is vitiated. The DBD that was used in this study is generated between two coaxial electrodes of which the outer one (conical copper electrode) is covered with a dielectric material made of quartz. The burner is modeled in a 2D-axisymmetric... 

In the present work, dynamic behavior of submerged slender bodies under external hydrodynamic forces with internal sloshing tanks is studied. The main application of this thesis is in submarines. For this purpose slender body theory is used for hydrodyanamics of body and unsteady hydrodynamics is used for the vehicle control fins. In submarines there are some water tanks that control the buoyancy, so that sloshing can be importatnt. An equivalent mechanical model is developed for simulating the dynamics of sloshing tanks. Assuming that a submarine is a slender body, elastic deformation of submarine body can affect dynamics of the whole system. Elastic behavior of the main body is simulated... 

In recent years, LBM has shown to be a suitable computational method for most flow simulations. Its simplicity, adaptability for complex geometries, and capability in parallel processing are among many reasons for broad implementation of LBM these days. In this research, we have tried to take advantage of these features in the simulation of a turbulent flow over a moving circular cylinder at low CPU cost. In order to use LBM in a high Reynolds number incompressible flow over a moving solid body, one needs to pay special attention to grid quality, curved solid wall boundary condition, turbulence model, moving boundary, etc. In order to obtain a suitable practical LBM computer code, the... 

Research on convective heat transfer coefficient around a rod bundle has several applications in industry. So far, many studies have been conducted in correlations related to internal fully developed flow. By comparing Dittus-Boelter, Sieder-Tate and Petukhov found to be more practical. The present study examines the validity of these frequently applied correlations experimentally. A thermohydraulic loop has been designed and manufactured to test and measuring the convective heat transfer coefficient. Due to its generalizibility, the unique geometry of this test facility (hexagonal arranged, 7 vertical rods in a hexagonal tube) has achieved extensive application. The major deviation factors... 

Moderate and Intense Low-oxygen Dilution(MILD) is the new member of combustion field. Highly preheated reactants and lowering the oxygen level in MILD combustion has some promising advantages. In this study the MILD burner, Jet-in-Hot-Coflow(JHC), is taken as the main test case. In this Research, Eddy Dissipation Concept combustion model ,introduced by Magnussen et al,is investigated in detail and governing equations are re-extracted. EDC combsution model due to moderate compuational cost in comparison with other combustion model and well prediction ability has drawn attention. Simulations on the Jet-in-Hot-Coflow(JHC) has shown the promising performance of the EDC combustion model. It seems... 

In order to study the interaction of sloshing and structural vibrations of baffled tanks a reduced order model based on modal analysis of structure model and boundary element method for fluids motion is developed. For this purpose the governing equations of elastic structure and incompressible flow used to derive simple models to simulate both fields. Using the modal analysis technique the structural motions are applied to the fluid model and on the other hand by using boundary element method the fluid loads are applied to the structural model. Based on this formulation a code is developed which is applicable to an arbitrary elastic tank with arbitrary arrangement of baffles. Results... 

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

Nowadays, reaching higher speed in marine crafts and underwater vehicles mostly requires a modern propulsor with high efficiency and enhanced cavitation performance. Because of these requirements, numerous researches for developing the existing propulsion systems and invention of new systems have been conducted in recent years. One of the most sophisticated and developed propulsion systems that have high hydrodynamic efficiency and high cavitation performance and low acoustic signature is pumpjet. This propulsor contains a rotor, stator and a duct that surrounds two other parts. Stator reduces the swirl of flow coming from rotor and thereby reduces the loss of energy. High cavitation... 

Long memory in assets return is important on the theoretical as well as the practical aspects and since it is a special form of nonlinear dynamics, in this study an ARFIMA model was used with the aim of considering the long memory in the return conditional average of automobile industry index. Then, due to the observation of ARCH effects, the simultaneous conditional average modeling and turbulences in the automotive industry index return using an ARFIMA-FIGARCH model was considered in the residuals of the best fitted model and results were that for modeling the returns and turbulences of automobile industry stocks which has a special long memory, FIGARCH will provide better and more... 

Nowadays, cleanrooms have a growing application in a broad range of industries, e.g. pharmacy, aerospace, nuclear energy and electronics. So, it seems that numerical modeling of airflow in such spaces becomes more essential. As computational fluid dynamics has become a powerful tool for indoor airflow studies, in this research, influence of effective parameters on the flow and concentration distribution in cleanrooms has been investigated by the use of CFD. To do so, aerosol flow in a 3-D cleanroom has been numerically modeled by Fluent 6.3, using Euler-Euler approach and standard k- turbulence model. Comparison between numerical results and experimental data shows a considerably good...