Sharif Digital Repository

Due to recent advances in laser technology and instruments, laser assisted machining processes has gained extra attention by scientists and industries. Naturally, effective modeling of the process is of great interest for researchers. Machining processes are generally modeled via FE tools and based on the requirements of model, it can be performed either mechanically or thermos-mechanically. About the LAM problems, it is basically meaningless to have a model without considering thermal effects. Hence, modeling is performed in two steps where through the first one, a thermal problem is solved to bring the temperature distribution of the work piece as the initial conditions of the next step.... 

This reaserch is study on the performance of evaporation tubes used in mini jet engines which has been done experimentally using laboratory equipment. In this study, researchers have tried to simulate the laboratory conditions as much as possible to the real conditions inside the mini-jet engine, increase the accuracy of the results and increase the results and bring them closer to the results inside the mini-jet engine. The experiments are divided into two categories, cold and hot In cold tests, an attempt is made to study and investigate the types of two-phase flow regimes created by applying different fluid and air flow rates, and to select annular flow regimes from among them.... 

Over the past five decades, the proliferation of electronic devices and the advent of Internet of Things (IoT) technology have ushered in a profound revolution in integrated circuit technology. In contemporary electronics, digital integrated circuits rely predominantly on CMOS transistors. Among the notable limitations associated with CMOS transistors are their non-zero off-state current and limited sub-threshold slope. In response to these limitations, researchers have ventured into a burgeoning field known as "Beyond CMOS," exploring technologies like Tunnel Junctions, Carbon Nanotube FETs, and more. Additionally, alternative approaches that blend electronic and mechanical principles in... 

Freely design and volume and fabrication cost reduction of electronic devices with three-dimensional structures are some of the improvements resulted from combining additive manufacturing with conductive inks that revolutionized the fabrication of practical electronic devices such as cell phones, computers, and satellites impressively. Although numerous processes of additive manufacturing have been proposed and implemented to fabricate electronic devices so far, the majority of these approaches have not only low speed and high components’ fabrication costs but also have many constraints in consumed materials. Therefore, the design and development of a novel additive manufacturing method to... 

The fused deposition modeling (FDM) process is an additive manufacturing technique that builds parts layer by layer. Unique advantages such as simplicity of operation, the ability to use a wide range of durable and stable polymer materials, and the ability to produce parts with complex geometry in minimal time and cost compared to other additive manufacturing methods have made this process highly attractive in recent years. However, parts printed with this process suffer from low surface quality and poor dimensional accuracy due to the layered construction. High surface roughness limits the application of these parts in many fields such as aerospace and medicine where precision and high... 

As humans age, the intervertebral discs in the spine lose some of their water content, reducing their flexibility and making them more prone to tears in the annulus fibrosus. When the annulus fibrosus weakens, the disc's nucleus can push through and cause a herniation, which can press on surrounding nerves and lead to severe pain. Each surgical method for treating disc herniation has its own complications and challenges. The gold standard treatment is fusion surgery, which fixes two vertebrae together, preventing natural movement in that part of the spine. This altered stress distribution on adjacent vertebrae can ultimately damage adjacent healthy discs over time. This research aims to use... 

Performance of reinforced concrete frames is highly dependent on detailing of the joint connections between its members, such as beams and columns. To have a good structural behavior, joints must show ductile behavior and designed based on the philosophy of strong column-weak beam. In the case of sever lacking ductility, strength or even rigidity of the connections, or having a weak column-strong beam, in the existing structures, there is a need for seismic upgrading of the connection. There are several ways for seismic upgrading of this type of connections.In this research, using steel plates for seismic upgrading of Concrete Beam-Column connections subjected to axial and cyclic loads has... 

In this thesis, we study security features of the networks which use linear network coding to multicast information to some nodes of the network in presence of a wiretapper and also an active intruder. We consider information theoretic security in which we assume no computation limits for enemy. Thus, we take advantage of the essence of network coding instead of cryptographic tools to improve security features of the network. First, we show how providing shannon security for such networks in presence of wiretapper, leads to different cost in multicast rate, depending on initial network code designed. Based on this, we present a modified secure network code design which can provide perfect... 

Two-phase fluid flow physics in porous media is applied in various fields. Studies have shown that wettability and surface tension, which represent fluid-rock and fluid-fluid interactions, have a significant effect on the dynamics of the immiscible displacement. Although the effects of wettability and surface tension on the macroscopic behavior of fluid flow are known, there is less understanding of it at the micro scale. Considering the essential role of wettability and surface tension in various fields, this project seeks to investigate the effects of wettability and surface tension on the movement and distribution of fluids and the dominant displacement mechanisms within the porous media... 

Optical tweezers consist of a tightly focused laser beam. A particle with refractive index greater than that of the surrounding medium can be trapped at the focus of the laser. The trapped object experiences a three-dimensional Hookean restoring force towards the focus. Nano (micron)-sized spheres can produce forces in the range of few pico-newton to few nano-newton. This range covers a large number of the forces, which contribute in biological processes; therefore, optical tweezers are very often used for micromanipulation of biological tissues. In a typical micromanipulation experiment it is crucial to perform proper positional calibration prior to use. There are several calibrate methods... 

The main goal of this research is to investigate the effects of different types of heterogeneities on fluid flow and solute transport in saturated porous media. These heterogeneities are micro- and macro-fractures and cavities. For modeling micro- and macro-fractures we used an equivalent continuum model and extended finite element, respectively. Also, we modeled the problem by using mass conservation law for both components of the problem – fluid flow and the solute – and Darcy’s law. In modeling vuggy porous media, due to the high velocity of the fluid inside the free flow areas i.e. channels and cavities, we could not model the medium properly using Darcy’s law. Therefore, we had to use a... 

Magnetic shape memory alloys (MSMAs) are a new class of smart materials that exhibit characteristics of large recoverable strains and high frequency. These unique characteristics, make MSMAs interesting materials for applications such as actuators, sensors, and energy harvesters. This thesis presents a three-dimensional phenomenological constitutive model for MSMAs, developed within the framework of irreversible continuum thermodynamics. To this end, a proper set of internal variables is introduced to reflect the microstructural consequences on the material macroscopic behavior. Moreover, a stress-dependent thermodynamic force threshold needed for variant reorientation is introduced which... 

Recently, there has been a surge of research activities in the area of networks in the systems and control community. One foundational class of questions on networked systems pertains to their controllability. While there are classical tests to check the controllability of linear time-invariant (LTI) systems, their applications to large-scale networks is numerically infeasible. Indeed, finding a minimum cardinality set of input nodes that ensure the controllability of a network is NP-hard. Moreover, when the interaction strengths along the edges of a network are unknown, the classical controllability test cannot be applied. To overcome these issues, an alternative set of approaches involves... 

Membrane bioreactors are increasingly being used for treatment of domestic and industrial effluents. A major operational drawback of this system is membrane fouling attributed to soluble microbial products (SMPs). In this study sampling were taken from microbial products on the surface and within the membrane pores and mixed liquir for mass characterization of protein content. Water-washing was used for surface and reversible portion of pore samples. Chemical wash with urea was used for further cleansing of SMPs within the pores. All samples were concentrate by precipitation with ammonium sulfate salt prior to analysis. Total protein content of samples was measured by lowry method. SDS-PAGE... 

The numerical modeling of engineering contact problems is one of the most difficult and demanding tasks in computational mechanics. Frictional contact can be observed in many problems; such as: crack propagation, metal forming operation, drilling pile etc. In metal forming operations the required shape changes are obtained by either of forming process, such as pressing, hammering, rolling or extruding the material between the tools which are much stiffer than shaped material. Because of large difference between deformability of the tool and material, relative movements occur in contact area. These relative movements produce the normal and tangential stresses, which have important role on... 

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... 

Growth of the fuel consumption in the world and the greenhouse effect of its pollution get industrial managers and environmental activities attention. Skin drag force has a significant role in energy uses. The drag reduction property of superhydrophobic surfaces shows a new approach for investigators to reduce energy uses. Surface with 150° contact angle called superhydrophobic surface.In this project, a superhydrophobic coating is developed based on acrylic hydroxyl resin by silica nanoparticles. This coating can be sprayed on any surface. Using the Iron oxid particles and silica nanoparticles together produces hierarchical micro-nano structures. This coating has a 160.1° contact angle on... 

In this thesis, optimal offering strategy problem of a virtual power plant (VPP) as a price-maker player in day-ahead frequency constrained electricity market is presented. The optimal offering strategy problem is modeled as a bi-level optimization problem. In the upper level, the total profit of VPP is maximized. In the lower level, the clearing conditions of frequency constrained electricity market is modeled. The proposed bi-level optimization problem is reformulated as a mathematical programming with equilibrium constraints (MPEC) problem by using Karush-Kuhn-Tucker (KKT) conditions. Then, the proposed MPEC problem, which is nonlinear and hard to solve by commercial solvers, is... 

One of the natural functions of wetlands is to neutralize the dangers caused by floods. Therefore, if a facility is built in the area of wetlands, it should not disturb their natural functioning. During the Iran-Iraq war, several antenna roads were built across the wetland, and the construction of these roads divided the wetland into 5 separate reservoirs. After the end of the war and with the development of the oil fields west of Karun (Hor al-Azim region), the extraction of oil from this region was put on the agenda. With the flood of April 2018, these facilities and roads were exposed to damage and flooding, and oil production from these reservoirs was stopped. In this research, after...