Sharif Digital Repository

Direct Metal Deposition is one of the methods of Additive manufacturing that has seen the most spread in recent years. In this method metal powder is directed towards the free surface of the workpiece through a nuzzle, and is simultaneously heated to become molten in a melting pool by a laser beam and begins the deposition process. One of the parts that make up a DMD system is powder feeding nuzzle. These nuzzles usually encounter a similar fundamental problem: that the effect of gravity on the stream of metal powder and the carrier fluid causes this stream to deviate from its intended position. To prevent this, nuzzles are usually designed with a fixed downward angle and the angle of the... 

Forging process is recognized as the high speed method, economical and with ability to produce high strength parts between metal forming processes. Preform design is the most important step in forging process. In the past this work was done based on experiences. In the complex parts because of error in design there was probability of diverse dies, so that method needed to spent so many times and costs. However recently with progress in computer programming we don’t need to produce diverse dies but spend many times. In this field many investigations are done to dispose designers skills, so forging preform design based on inverse finite elements method is denoted for this gold. In this thesis... 

Nanopositioning is technology of positioning & manipulation of Nano-scale object. This technology can be considered as one of the fundamental necessities in Nano & Micro research and fabrication and made lots of unbelievable advancement in researches and technologies. There are lots of mechanical systems designed for large scale positioning with sub millimeter resolution, but when it’s come to Nano scale, the range of access should be limited to some micrometer. Also in Nano-scale motion some difficulties like backlash, stick-slip and friction is phenomenon. For increasing the workspace using coarse and fine positioning systems may be an appropriate method. In this method a fine positioning... 

In this work, a direct design approach for designing a surface shape (inverse design problem) has been developed in which both the target surface pressure and the unknown nodal coordinates appear explicitly in the formulations. The final discretized form of the governing equations (unified formulation) can be used for both analysis and shape design problems. Shape design problems in the context of the steady inviscid and compressible flow, based on the three-dimensional Euler equations, were directly solved to achieve a prescribed pressure along the solid boundaries. The AUSM+ scheme was used to discretize the flux terms in the Euler equations, in which the inviscid flux is splitted into... 

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... 

With the increasing tendency of consumers to purchase from online stores and the remarkable growth of this industry in recent years, timely and cost-efficient delivery of goods to the final customer has become one of its major challenges. Accordingly, last-mile delivery has attracted significant attention from both researchers and practitioners. This study addresses a vehicle routing problem that considers customers’ ability to pick up their orders from selected centers and their possible presence at different locations within the planning horizon. This thesis aims to enhance customer satisfaction and reduce distribution costs by employing two innovative vehicle routing approaches. The first... 

Shock control bump (SCB) and suction and blowing are flow control methods used to control the shock wave/boundary layer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. A SCB uses a small local surface deformation to reduce the shock-wave strength, while suction decreases the boundary-layer thickness and blowing delays the flow separation. Here, a single-point, a multi-point, and a robust optimization method are used to find the optimum design of SCB and suction and blowing. The flow control methods are used separately or together on two transonic airfoils i.e.; RAE-2822 and NACA-64A010 for a wide range of off-design transonic Mach numbers. The RANS flow... 

Developers often seek to find projects that match their topics of interest in version control systems with the goal of reusing code, extracting similar requirements, learning, and more. However, due to the widespread use of these systems, the number of projects maintained on them is huge and ever-increasing. This has made it difficult to identify projects based on their topics. GitHub, as a prominent version control system, with the aim of facilitating access to projects based on their topics, has provided the possibility of assigning software topics to projects in the form of free-text tags for users. Assigning a correct and complete set of topics to software projects allows programmers to... 

The present study evaluates the effect of connection rigidity on the behaviour of partially restrained frames under fire condition. Since the interaction of members with each other at elevated temperatures, controlled by the connections, has a significant effect on the behavior of the structure, a half-scaled three dimensional one-bay, one-story frame was used as the test specimen. In fact, this study is part of a broader research programme in which identical specimens equipped with similar connections (flush endplate connections) with various thicknesses hence various rigidities are studied. In order to record the deformations of structural members and the rotation of connections, Digital...