Sharif Digital Repository

The theory of resonant wave interaction has found considerable applications in meteorology, oceanography and limnology. It is known that the mechanism serves as an effective means of energy transfer in the atmosphere, oceans and lakes. In this project, the three-dimensional resonant interaction of a surface wave with two pairs of interfacial waves in a stratified fluid is studied theoretically. Witham’s variational method is formulated in order to apply to weak resonant interaction among waves whose amplitudes and phase angles vary slowly with position and time. The method is applied to a surface-interfacial wave interaction in a horizontally infinite two layer fluid. Combination of two... 

Nowadays, a wind tunnel is a tool used in aerodynamic research to study the effects of air moving past solid objects. By employing a wind tunnel, we can compeletely control the conditions of aerodynamic testing on specific models. In this research, the design of a diffuser for the subsonic wind tunnel has been taken into account by CFD. The wind tunnel is of suction type and is powered by three axial fans which are manufactured by LTG Inc. The tunnel test section has a 140 cm height and 195cm width which can provide a necessary Mach number. Considering the setting of the three axial fans, located at the end of the diffuser and parallel to each other, it’s necessary to take into consideration... 

For along time, analysis of financial markets is an interesting topic for mankind. There are different statistical methods to analyze financial time series. In this manuscript, financial markets are analyzed from network view point. Inference of hidden structures between companies of a market is merit information so we introduce different methods to infer
hidden network structure of financial markets. In addition, we will show that dynamic of network structure can provide important information about external sources of influence on financial markets. Actually, we show affect of political events on financial market of Iran. At last, we generalize diffusion concept at financial networks... 

High-altitude simulation lab of chemical thrusters is one of the most important infrastructures for the development of space thrusters technology. In these laboratories, different sections are designed according to the requirements for simulation of the thrusters at specific pressure and temperature. The purpose of this research is to design a subset of the creation and preservation of vacuum for the purpose of ground testing of chemical thrusters. Vacuum preservation is more comprehensive than the vacuum creation and is usually the bottleneck of design, so the design of this subset is intended in the present study. To illustrate this, after introducing the basic concepts required, two... 

By developing composites, difficulties of modeling of degradation of properties as stiffness is most considered. The recent advances in the modeling of degradations in stratified composites have led to improved models on all scales. Macro scales methods are good to estimate fracture but not to estimate the failure in micro scale (as microcrack) and moreover, they need many experimental data. Therefore by considering a stratified structure which contains fiber, matrix and intermediate area, mesoscale modeling method is most suitable. In this research Micromechanical Progressive Algorithm (MPA) is used. The method employed is Micromechanic Method of Fracture (MMF). In this work by developing a... 

The purpose of this research is providing the preliminary study and designing, fabricating and installing diffuser vanes on the vaneless diffuser compressor to improve its overall performance. To meet the goal, the GT4082 turbocharger centrifugal compressor is chosen as the basis unit. The compressor is fully modeled, to predict the compressor performance curves. One dimensional and three dimensional models are provided, to simulate the compressor with vaneless diffuser as well as vaned diffuser. In one dimensional model, governing equations are continuity, energy, and state and also the empirical components losses coefficients of the compressor are used. In this method, fluid properties are... 

The progress in the design of nano-scale machines over the past decade has motivated researchers to study the concept of nano-communications. Inspired by biological systems,diffusion-based molecular communication (MC) systems have been proposed as a potential solution for communication in nano-networks where molecules are used as information carriers.Nano-networks are envisioned to facilitate revolutionary applications in areas such as biological engineering, healthcare, and environmental monitoring. In recent years, there has been a significant amount of work on various aspects of MC systems, including transmitter and receiver design, multiple access protocols, and network layer issues.... 

Chaotic and resonant Dynamics of full two body problem are investigated through the sphere-ellipsoid and ellipsoid-ellipsoid models. The fourth-order mutual gravitational potential function is derived in terms of the first-order moment of inertia for both models. Employing Hamiltonian formulation and elliptical expansion, the resonant angles appear in the equations which include secondary’s attitude and mean anomaly for sphere-ellipsoid model and attitude of both bodies and mean anomaly for ellipsoid-ellipsoid model. In first step, resonances overlapping criteria is applied to the first-order resonances of sphere-ellipsoid model and the effect of the asphericity and orbital eccentricity on... 

In this project, we are willing to analyze and design a subsonic wind tunnel WT configuration for the Aerospace Engineering Department in Sharif University of Technology. This WT will be an open-circuit "suck down" type, whose entry is open to the atmosphere (laboratory) and three axial fans downstream of its test section. In addition to three parallel fans, we are expected to design two simultaneous small and large size test sections for it. The small and large sections would have an area about 1.4 and 4 m2and maintain a maximum air velocity of 100 and 50 m/s, respectively. So, our design is faced with two main complexities. In one hand, we are to manage the air flow through these two test... 

Cleanrooms have been widely used in many industries. The main goal in designing a clean space is to control the level of particles concentration. As a result, introduction, generation, and retention of airborne particles inside the environment need to be minimized. In this research, the effects of main parameters on the generation and deposition of particles through cleanrooms have been numerically investigated. At first, the role of geometric features of swirl diffusers on the induction effect and the resultant air mixing has been evaluated. Using parametric study approach, the diffuser geometry has been optimized and sensitivity of its optimum features to the airflow rate has been... 

The elastic field is one of the challenges in optimizing the lifetime and capacity of the lithiumion batteries. Graphite nanoparticles have been widely used in Li-ion batteries, due to their mechanical, thermal and electrical properties. During the lithiation, chemical reactions occurred in the electrolyte, which forms a solid electrolyte interphase(SEI) in the surrounding of nanoparticles as well as stress fields inside the nanoparticles. Therefore, the purpose of this research is to examine the effects of the surface/interface on diffusion induced stresses(DIS) within core-shell nanosphere due to non-uniform distribution of eigenstrain fields. Due to the mechanical behavior of the phases,... 

The elastic field is one of the challenges in optimizing the lifetime and capacity of the lithium-ion batteries. Graphite nanoparticles have been widely used in Li-ion batteries, due to their mechanical, thermal and electrical properties. During the lithiation, chemical reactions occurred in the electrolyte, which forms a solid electrolyte interphase(SEI) in the surrounding of nanoparticles as well as stress fields inside the nanoparticles. Therefore, the purpose of this research is to examine the effects of the surface/interface on diffusion induced stresses(DIS) within core-shell nanosphere due to non-uniform distribution of eigenstrain fields. Due to the mechanical behavior of the phases,... 

In the present thesis, the SPASER is investigated, from theory to structure design. SPASER is a counterpart of laser in 3D subwavelength dimentions. In other words, SPASER does not suffer from the diffraction limit of photons which is a drawback in laser technology. It potentially can generate intense coherent dark and bright surface plasmon modes. The small size of SPASER gives it the capability of being integrated with electronic chips. So, the electronic technology will become faster if the SPASER is realized. In this thesis, we intend to use the unique plasmonic properties of graphene in our designs. Plasmons on graphene platforms have longer propagation length and larger lifetime in... 

Among the various materials, silicon anodes have the highest lithium absorption in lithium-ion batteries. But this high lithium absorption capacity can cause 300 percent volume expansion and large stresses. Experimental observations show that charge and discharge cycles may cause plastic deformation in some parts of the electrode particle. On the other hand, there is a possibility of a ratcheting phenomenon due to changing in elastic properties of the electrode material during the charging and discharging processes. However, this phenomenon has not been reported for silicon spherical electrode particles yet.This study aims to model the elastic-plastic behavior of silicon spherical electrode... 

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... 

Type IV high pressure vessels are composite vessels with a polymeric liner, which are the best choice for storing hydrogen in hydrogen vehicles. The defect of these vessels is the penetration of light hydrogen molecules in the polymeric liner and the composite part. When depressurization the vessel, these molecules cannot release from the polymeric liner and the composite part according to the emptying rate of the vessel. Thus, concentration of the hydrogen molecules in the polymeric liner becomes more than inside the vessel which leads to a pressure difference between the two sides of the polymeric liner that causes the liner collapse. In this research, the partial differential equation for... 

Many heart attacks and strokes are caused by improper clot formation in the vascular system. Mathematical understanding of the clot formation process and the influence of various factors in the clot formation process is very important. In this study, the aim is to simulate and understand the clotting process mathematically by considering natural, external and general mechanisms in the clotting process. In this process, when damage occurs in the endothelial region of the vessel, tissue factor is released and 38 different substances react with each other inside the plasma, eventually forming fibrin. To simulate the movement of different chemical components and proteins in plasma, the... 

Gas injection is known as a promising Enhanced Oil Recovery (EOR) method for oil recovery in naturally fractured reservoirs. Gravity drainage is the main production mechanism in such reservoir, which also is affected by molecular diffusion in the case of non-equilibrium gas injection. Formation of liquid bridge in fractures between overlying matrix blocks leads to capillary continuity between blocks and subsequent increase of oil recovery. The aim of this study is to determine the required conditions for formation, stability and fracture capillary pressure of liquid bridge and investigation the role of fracture surface roughness, wettability, oil and gas properties, flow conditions and mass... 

Nanomachines are molecules inspired by natural molecular machines and are able to move and transport at the nanoscale. Due to the advancement of nanotechnology, the need to move materials and energy on a small scale is necessary more than ever. Nanocars are artificial molecular machines with chassis, axles, and wheels designed for nanoscale transport at materials’ surfaces. Understanding the dependence of surface dynamics of nanocars on the substrate’s physico-chemical properties is critical to the design of the transport properties of such man-made nanoscale devices. Among the multitude of potential substrates for the nanotransporters, graphene exhibits intrinsic ripples on its surface,... 

Thermal penetration is one of the separation methods. In this process, due to the temperature difference, the concentration gradient in one of the gas or liquid phases in the resulting system and the relative separation of the components is possible. The column used for this work is the Classius-Dickel column. This column consists of two vertical plates, one warm and the other cold, spaced a short distance apart. Due to the temperature gradient, the gradient is deliberately created, which creates a concentration gradient in the column, so that the light component accumulates at the top of the column and the heavy component at the bottom of the column. The difference in concentration between...