Sharif Digital Repository

Nowadays, due to the increase in energy demand and the limitations of using fossil fuels, renewable energy plays an important role in the world's energy supply. Wind turbines generate electrical power using the kinetic energy of the wind. This research investigates the effects of dust and particles on the flow in a vertical axis wind turbine blades. The performance of a H-type vertical axis wind turbine in dusty flow was numerically investigated in two and three dimensions. The effects of two dimensionless numbers (Stokes and particle loading) on the turbine’s aerodynamics and output power were examined. In addition, the erosion rate of turbine blades due to dust particles and turbine... 

Bubble collapse is a two-phase problem whose numerical simulation has many important applications in science and technology. In hydrodynamics systems (pumps, ship propellers, …), bubbles form due to cavitation. These bubbles grow and collapse These bubbles grow and collapse farther downstream and their energy destroys the surrounding walls. In medical sciences, the shear force caused by collapse of a bubble can be used to destroy adipose tissues in arteries. The small scales time in this phenomenon, as well as the compressibility of the flow in bubble collapse, are interesting challenges researchers face. The present thesis targets are two-dimensional numerical simulation of bubble collapse... 

Based on the history of computational fluid dynamics, choosing a proper method for three-dimensional investigation of two-phase flows is always challenging. In this research, the flow of atomization of a liquid jet was investigated. Also, Using GPU technique made our computations about 40 times faster. The numerical results are in good agreement with available numerical and experimental data. Based on our results, jet flow can achieve different regimes at different Weber and Reynold. Jet flow was found in dripping and Rayleigh instability regimes when Weber number was set to 1.79 and 3.10, respectively. Also, the transition between dripping and jetting was estimated at We between 2 to 3. In... 

Rapid preparation of a homogeneous mixture is essential for many chemical and biological applications, such as micro-scale biological-chemical agent detection, drug delivery, and DNA hybridization. Some mixing systems have a micro-scale geometry, which results in a very slow mixing process, mainly due to laminar flow in these systems. Mixing in a slow flow is performed only by molecular diffusion. In the absence of any disturbances, increased mixing is not possible simply by diffusion. Accordingly, a suitable and innovative method to improve mixing for such systems is required. Induced charge electro-osmosis is a new field of electro-osmotic flow, which performs better than conventional... 

Nowadays, air pollution has become one of the biggest problem of large cities and has numerous negative effects on the environment and people's health. The present research examines how various types of pollutants are distributed in an urban environment, depending on the type of arrangement in different places. Razaviyeh town (including nine 15-story buildings) in the 9th phase of Pardis new city in Tehran has been studied three-dimensionally here. The dimensions of each building in this complex are 12 x 13.5 meters and their height is about 45 meters. Thus, the dimensions of the computational domain used are estimated to be less than 0.02 square kilometers. In this research, computational... 

Interaction of vortices with particles is one of the complex and fascinating phenomena in fluid dynamics, which is often observed in wind turbines operating in dusty environments. In these turbines, dynamic stall occurs where vortices continuously form and dissipate. In this study, the impact of the presence of dust particles on dynamic stall, which can noticeably affect the aerodynamic efficiency of wind turbines, has been examined and analyzed; We focus on three airfoil models of the horizontal-axis wind turbines. namely S809, S822, and SD7062 at a Reynolds number of 10^6. These were examined using numerical simulation, with k-ω SST turbulence model and discrete phase model (DPM). The... 

Security has been considered from the information theoretic point of view in different channels such as broadcast, multiple access and relay channels. Due to application of these channels in modern networks such as wireless, sensor and Ad-hoc networks, information theoretic security arguments especially wiretapping, has major significance in these networks. With regard to necessity of confidentiality protection in modern telecommunication services, security from the information theoretic point of view should be considered as well as capacity and achievable rate region considerations in these networks. In this thesis, first, a survey of basic works in the subjects of secrecy capacity and... 

The Phenomena of generation and propagation of pressure waves (e.g. sounds) are of fundamental importance in studying fluid dynamics. Conventional computational fluid dynamics (CFD) simulations has always been part of the investigation. On the other hand, the lattice Boltzmann method (LBM) has been developed into an alternative and promising numerical method for simulating sound propagation in heterogeneous media with complex geometries. In this project, propagation of sound waves in a liquid was simulated, using lattice Boltzmann method (LBM) and particularly phononic model. To survey effect of different viscosities on this phenomenon, the kinematic viscosity of the medium was varied and... 

Nowadays, BDI architecture is of the most well known agent’s architectures. BDI architecture or the architecture in which the system is viewed as rational agents based on the attitudes of belief, desire and intention represents an abstraction of human deliberation based on a theory of rational action in the human cognition process. BDI logic introduced by Rao and Georgeff have been widely used as the theoretical basis of specification and implementation of rational agents. BDI logic is limited to deal with crisp assertion, while the assertions encountered in real world are not precise and thus cannot be treated simply by using yes or no. Moreover, In order to obtain more human like agents we... 

Drop formation is an interesting field of research due to its wide-range of applications, such as drug delivery, biomedical studies, pharmaceutical industry, Lab-On-Chip (LOC) devices, etc. In recent years, researchers have used numerical studies to better understand how the process of forming and carefully examining the factors that affect quality improvement. One of the most effective methods in controlling the size and the process of drop formation is use of external force in microfluidic devices. Among the external force in this study, an electric field with oscillating current was used. Rapid methods for creating, deforming, and breaking up of drops in microfluidic applications are... 

One of the most powerful means to increase thermal efficiency in gas turbines is to increase the turbine inlet temperature. However, due to metallurgical limitations, the turbine blades need to be cooled constantly. Thus, film cooling of blades has shown to be the most efficient way. In this study, a three-dimensional film cooling problem at jet Reynolds number of 4700 are investigated, using RANS approach and three different turbulence models, namely (Wilcox), SST(Shear Stress Transport), and the new model. A fine non-uniform staggered grid and a SIMPLE based finite volume method were used. Film cooling simulation results, including mean velocity components and turbulent kinetic energy... 

Considering the wide range of applications of porous media for heat transfer enhancement in various components of industrial machineries, including solar collectors, air dryers, compact heat exchangers, electronic microchips, investigation of heat transfer characteristics in porous media has been a major concern for many researchers. On the other hand, precise understanding of the physics of porous media-flow interaction has been an open research topic for a long time. The present research however, has aimed at developing a computational method to simulate the interaction between fluid flow and porous media to investigate heat transfer from prously covered surfaces. Pore scale modeling of... 

High-quality online services demand reliable and fast packet delivery at the network layer. However, clear evidence documents the existence of compromised routers in the ISP and enterprise networks, threatening network availability and reliability. A compromised router can stealthily drop, modify, inject, or delay packets in the forwarding path to launch Denial-of-Service, surveillance, man-in-the-middle attacks, etc. So researches tried to create intrusion detection methods to identify adversarial routers and switches. To this end, data-plane fault localization (FL) aims to identify faulty links and is an effective means of achieving high network availability. FL protocols use... 

Confining nematic liquid crystal between two curved boundary conditions while the nematic molecules have a degenerate planar anchoring leads to complex and beautiful textures of molecular disparagement(defect) in the bulk and on the surfaces. Such the liquid crystal shells are made with double-emulsion techniques in microfluidic devices have provided applications for micro-scale colloidal linkers.In this work, we have numerically minimized the elastic energy in one-constant approximation in present of Fournier’s degenerate surface potential with finite element method. The nematic shell is confined between two spherical surfaces that we have studied the final energies and their related... 

Pretreatment of nuclear waste for valuable and limited uranium resources in the nuclear industry as well as environmental protection is imperative. Wash the affected parts of the Natanz uranium enrichment plant uranium centrifuges with a standard cleaning solution of citric acid, a liquid waste is generated in this study, the preparation of these residues using supercritical water oxidation (SCWO) and near critical (HTWO1) was studied as a result, the optimum operating conditions, and conditions of solvent extraction has been studied. In the result, the optimum operating conditions, and conditions of solvent extraction has been introduced. Also in the UCF2 as a liquid waste contaminated with... 

A liquid crystal is a state of matter composed of highly anisotropic building blocks. When liquid crystals are exposed to surfaces with given shapes and anchoring conditions, the orientation of their molecules gets spatially disordered and topological defects may form in the system. The interplay between liquid crystals and the geometry and topology of the colloidal particles has motivated extensive recent studies.In this thesis, we present the numerical modeling results for two faceted colloidal particles in a thermotropic nematic liquid crystal. To obtain the equilibrium nematic field with a finiteelement method, we numerically minimize the free energy of the system that based on the... 

Providing high bandwidth network infrastructures for ever increasing need of data transport is of great importance. The underling infrastructure for many communication services such as GSM/3G/4G mobile networks and Internet services is Synchronous Digital Hierarchy (SDH) optical transport systems. SDH are standardized protocols that multiplex multiple lower rate digital bit streams, such as E1 and Ethernet, and transfer them synchronously over optical fiber using lasers or LEDs. In addition to high data transfer rates, flexible network management and protection mechanisms have great importance, hence are part of SDH standards. In order to obtain flexible network architecture and protected... 

Development of Smart Grid and deployment of smart meters in large scale has raised a lot of concerns regarding customers’ privacy. Consequently, several schemes have been proposed to overcome the above mentioned issue. These schemes mainly rely on data aggregation as a method of protecting users’ privacy from the grid operators. However, the main problem with most of these schemes is the fact that they require a large amount of processing power at the meter side. This, together with the fact that smart meters don’t usually have a powerful processor, can cause the unavailability of smart meter data at the required time for operators of the grid, and at the same time disables smart meters from...