Sharif Digital Repository

The rapid development and growth of the offshore turbine industry has led to the construction of offshore wind farms in earthquake-prone areas, and due to the shape of the structural system, which consists of a long cylindrical tube with a heavy mass on top of it, this structure is a sensitive structure. It has a dynamic behavior, and many environmental loads such as wind load, wave load, current load, and earthquake load in seismic areas are dynamic in nature. In this research, it investigates the seismic dynamic behavior of 5MW offshore wind turbine using the ISO-19901-2 standard and the Endurance Time method. In the modeling of this structure, Soil Structure interaction and Fluid... 

Inlets must decelerate the air with lowest loss and drag together with a given pressure and Mach number with best quality and uniformity to the engine. This is done based on flight Mach number, by an arrangement of shock waves and surfaces gradient in the inlet. Any distortion in the flow field and the inlet geometry parameters may disrupt such arrangement and influence on the inlet performance, in addition, under critical conditions, it might affect the stability of the intakes. Any distortion in the flow field and the inlet geometry parameters may disrupt such arrangement and influence on the inlet performance, in addition, under critical conditions, it might affect the stability of the... 

In present study, various cocatalysts were used to improve catalytic properties of metal oxides and oxy-acids. Ag3VO4/Ag3PO4/Ag and Cu2O/MoS2/rGO photocatalysts were synthesized. The photocatalytic activities of the prepared nanocomposites were evaluated by the photodegradation of dye in the heterogenous systems as a series of advanced oxidation reactions. The results revealed that heterojunction between two semiconductors may prevent fast electron-hole pair recombination and then improve efficiency and rate of dye photodegradation. Mechanism and kinetics of dye degradation were studied in the presence of new photocatalysts by using of different scavengers. In the other works, Pt-NiO/G and... 

Amount of strain has been always considered as the primary parameter affecting the microstructural and strength evolutions during Severe Plastic Deformation (SPD). However, these evolutions unavoidably saturate in large strains under deformation with constant conditions, i.e. constant deformation temperature, strain rate and strain path. In this study, effects of these factors on the microstructural and flow behavior of Ultra-Fine Grain (UFG) aluminum (AA 1050 and AA 5052) processed by Accumulative Roll-Bonding (ARB) are investigated. The flow behavior and its time-dependent aspect are evaluated up to large strains by Plane Strain Compression (PSC) and Stress Relaxation (SR) tests. ... 

In this research, aluminium sandwich structure was manufactured by accumulative roll bonding (ARB). In this method, aluminum AA5083 strip was used as the matrix and titanium hydride was selected as the foaming agent powder. Due to the use of particle foaming agent in the first pass, reduction, preheat temperature, rolling speed and the percentage of powder particles parameters were examined. Finally, the 66% reduction, 400 °C preheat temperature and 25 rpm rolling speed, were considered as the optimal values. At the next stage of this process 50% reduction was applied at each pass and this process was repeated up to five passes. After ward, in order to create a sandwich structure, aluminum... 

In this study, utilizing the so-called “flow forming”, a cold-bonding process is developed to produce multi-layered thin-walled tubes and cylinders. In this process, which is entitled as “spin-bonding”, two layers of tubes are bonded by thickness reduction. Al/Al and Cu/Al tubes were bonded at various temperatures, thickness reductions, feed rates and roller attack angles. The bonding quality was examined by peel test, metallography and SEM fractography. Moreover, spin-bonding was accumulatively applied to aluminum tubes up to 4 cycles as a severe plastic deformation (SPD) for thin-walled tubes and cylinders entitled as “Accumulative Spin-Bonding” (ASB). Beside of experimental works,... 

In the roll bonding process, the same and non-homogeneous metals are bonded to each other by rolling deformation, and the sheet produced exhibits multi-properties. Two- and three-layer copper and stainless steel sheets are used for a variety of purposes. Stainless steel-Copper bilayer sheets are not just cost effective in production, but also have mechanical and thermal benefits from the inherent properties of copper and stainless steel. In addition to its increased strength, good ductility, reduced thermal expansion and excellent soldering are other benefits. In the past, some researchers have been studied on the bonding strength and formability of austenitic stainless steel-copper bilayer... 

Crop classification is one of the most important applications of remote sensing in agriculture. Knowing what crops are on the farm is invaluable both on a micro and macro scale. For example, this information can be used to design and imple- ment agricultural policies, product management and ensure food security. Also, this information can be used as a prerequisite for implementing other programs at the farm scale, such as monitoring and detecting anomalies during the crop growth cycle. Most of the studies in this field are focused on the optical data of the Sentinel-2 satel- lite, but the optical data are vulnerable to atmospheric conditions, and on the other hand, there is valuable... 

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... 

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... 

Secure routing is a major key to service maintenance in wireless ad hoc networks. Ad hoc nature exposes the network to several types of node misbehavior or attacks. Wormhole attack is one of the most severe active attacks to mobile ad hoc networks. Noting the resource limitations in such networks, nodes may have a tendency to behave selfishly. Selfish behavior can have drastic impacts on network performance. We have proposed a Misbehavior-Tolerant Multipath Routing protocol (MTMR) which detects and punishes all types of misbehavior such as selfish behavior, wormhole, sinkhole and grey-hole attacks. The protocol utilizes a proactive approach to enforce cooperation. In addition, it uses a... 

Dynamic spectrum access with the aid of cognitive radio (CR) technology is a viable solution to spectrum scarcity. There are many military and emergency applications that require the use of cognitive radio ad-hoc networks (CRAHNs). In these net- works, nodes must first find each other in a wide spectrum and then exchange their desired data. The process of finding each other in a multichannel environment is a challenging task and is usually known as rendezvous. Since rendezvous is the first step in communication, disrupting will disable the nodes from establishing proper communication sessions. That results in a drastic degrade in the performance of the network. Therefore, it is important to... 

Spray-wall impingement is one of the phenomenon that associated in different subject such as spray cooling, combustion chamber and gas turbine. With the impingement of spray to the wall, liquid film begins to form. Wall film characteristics is still an important subject to study. Due to the various stages of liquid film formation from injection of spray till spray-wall impingement, the investigation of this phenomenon is far more complicated. This paper is meant to provide detailed data on spray-wall impingement and wall film formation physics with the help of computational analysis of OpenFOAM . A Lagrangian-Eulerian method based on discrete phase model (DPM) was employed to model... 

Lattice materials with periodic reticulated meso-truss architectures, frequently inspired by nature, are man-made materials offering outstanding stiffness-to-weight ratios which make them an excellent candidate for lightweight structures. Focusing on the metallic pyramidal lattice material for its remarkable applications especially in ultra-light energy absorbers, in the scale of representative volume element (RVE), an analytical framework using beam theory is presented to explore the anisotropic effective elastic properties of this lattice material. Utilizing hollow-tapered struts as the constituent of pyramidal lattices, superior effective stiffness as well as yield strength for the same...