Sharif Digital Repository

Optimization of Plate-Fin Heat Exchnagers, which have various applications in different cryogenic processes nowadays, can have a significant role in improving process efficiency as well as decreasing their capital and operationl costs. In this study, is introduced a procedure to optimize the performance of multi-stream multi-phase Plate-Fin Heat Exchangers, implementing Genetic Algorithm optimization method. In this study, the simulation of the multi-stream multi-phase Plate-Fin Heat Exchanger is carried out by Aspen EDR, a leading software in simulation and design of different types of heat exchangers. The software is then integrated to external software to automate the simulation... 

Nanocrystalline steel was developed by severe cold-rolling and subsequent annealing of HSLA steel with an original microstructure of lath martensite. Specimens are austenitized at 1000 ºC for 30 min followed by quenching in brine. The quenched specimens are cold rolled with 80% to 90 % reduction and then annealed at temperatures from 400 to 700ºC for 10 to 120 min.The specimens annealed at temperature 500oC for 60 min showed the multiphased ultrafine structure composed of equiaxed ultrafine ferrite grains with the mean grain size of 180 nm, nano-carbides distributed uniformly and blocks of tempered martensite. The produced nanostructured steel exhibited a yield stress and UTS, of 1280 MPa... 

The news headlines should represent the main and the most important topics of their stories. The task of selecting an appropriate headline for news stories is mainly done by journalists. The goal of this project has been the design and implementation of a system to automate this task, that is generating headlines for news. This task has been done for Persian news stories. There are various methods for automatic headline generation in English and some other languages, but no work has been done for Persian, yet. Thus, we have adopted some of the ideas from those methods, and do the remaining by our initiation. Our proposed method consists of three main parts: keyword extraction, most important... 

Pipe freezing has become well established in industry as a method of short-termisolation in order to carry out maintenance or repairs. It is often necessary to repair system components without plant shutdown or drainage of system having many piping structures which may have hazardous or expensive fluid. Therefore, a series of tests has been arranged to investigate the ice plug formation in two standard pipes with different diameter size. The freeze zone on the pipe has been created by means of an aluminum jacket which liquid nitrogen flows in it. In the tests the freezing time, amount of liquid nitrogen usage andthe pressure tolerance of ice plug have been determined. Moreover, the numerical... 

In recent years, the area of research on micro flying robots has been developed due to the development in micro manufacturing technologies. Due to extra advantages of these flying robots, they are implemented in military and civilian missions such as identifying, espionage, aerial relays, traffic surveillance, rescue, aid, etc. Ability to fly in specified areas, without human injuries, low manufacturing and energy costs, easy and fast implementation, Easy Maintenance, etc, which are some advantages of these robots. We can control these robots manually by remote controllers (RC) or by Auto guidance systems. On the other hand, these robots are used in research laboratories for testing new... 

Range Profile (RP) is known as one of the most important tools for radar target recognition. The main problem with range profile for radar target recognition is its sensitivity to aspect angle. To overcome this problem, range profiles are assumed to have the same statistical characteristics in small frames of aspect angles or context dependent models such as HMM may be used. All methods presented, seems to have some shortcomings to offer a model based on physical circumstances of target maneuver. For example in such models, consecutive samples of RPs in an aspect frame are assumed to be statistically independent with the same distribution (IID). Here we propose dynamic system (DS) for... 

The present thesis aims at investigating the dynamic interaction of slosh and aeroelasticity in the fuel contained aero vehicles. The main approach in this research is to develop reduced order models for description of the coupled system. In this regard, boundary element method is used to develop slosh dynamic model. Axisymmetric boundary element method with non-symmetric boundary conditions is used to develop slosh dynamic model for axisymmetric containers. Zoning method is used to develop slosh dynamic model for the multi-baffled tanks and based on it, slosh equivalent mechanical model is developed for multi-baffled tanks. Finite element method along with modal technique is used to develop... 

There are numerous ways available to achieve low temperatures that cryocoolers might be among the most important of them. In the meantime, the pulse tube refrigerator has a special place due to its simple geometry and not be using any moving parts. This simple property make the pulse tube refrigerator one of the most popular methods to achieve low temperatures. Nowadays, a pulse tube refrigerator is used for cooling in the range of 4 to 123 Kelvin in two form of one-stage and two-stage and up to an approximate power of 1 KW. Today, due to the temperature and the amount of power required for cooling, as well as the time it takes to reach that temperature, this chiller is used in medical,... 

During the last few years, the study of urban environment structures is considered as a research field of interest in remote sensing. In satellite observations of the earth's surface, continuous imaging in terms of time and space has caused the remote sensing technique to be proposed as a useful and efficient tool for the analysis of urban areas. Obtaining quantitative spatial information from the urban environment in fields such as determining the height of buildings plays an essential role in urban planning, monitoring damage to buildings, establishing communication bases and digital cities. During the last two decades, the use of Tomosar approach in order to reconstruct the structures of... 

In this thesis we consider the effect of random locations of users in the capacity analysis of SIR-based power control systems and comparison to the strength-based systems, for the first time. Unlike previous works we do not consider a simple deterministic uniform model for the analysis. We provide simulations and analytical solutions for calculating the interference statistics, based on which, we not only calculate the interference statistics, but also study the effect of locating a user in every location in the network coverage area and its share in the interference. We also calculate each cell’s share in every statistics of the interference. In this thesis, based on the common assumption... 

In synthetic aperture radar (SAR) satellites, the nadir echo is defined as the backscattered signal from the point directly below the satellite on the earth surface. If the timing of the radar is such that the nadir echo arrives at the receiver while the receiver is turned on for receiving the desired signal, it could damage the receiver or disrupt the resulting SAR image, unless it is suppressed enough by proper design of antenna radiation pattern. In current SAR satellites, ”avoiding” this phenomenon is associated with two problems: 1) limiting the swath width, 2) imposing stringent restrictions on the selection of pulse repeatition frequency (PRF). Therefore, ”suppressing” the nadir echo,... 

Localization of radio sources has various applications in civil and military communications. Some of important localization methods consist of Angle of Arrival (AoA) estimation of the illuminated signals from the interested sources. Between various Direction Finding (DF) methods, subspace based methods are of special importance, because of their high resolution and accuracy. And from beginning of invention, because of new challenges, have been focus of numerous researches. In this thesis, first we explain the most important subspace based DF methods called MUSIC and root-MUSIC. Then a novel modification for root-MUSIC is introduced. In our new method the computational complexity of... 

In order to study the interaction of sloshing and structural vibrations of baffled tanks a reduced order model based on modal analysis of structure model and boundary element method for fluids motion is developed. For this purpose the governing equations of elastic structure and incompressible flow used to derive simple models to simulate both fields. Using the modal analysis technique the structural motions are applied to the fluid model and on the other hand by using boundary element method the fluid loads are applied to the structural model. Based on this formulation a code is developed which is applicable to an arbitrary elastic tank with arbitrary arrangement of baffles. Results... 

The aim of this article is ancestral control of a set of 3-wheel robots with non-holonomics dynamics for hunting and covering around moving target. Robots have mass and inertia and the wheels' mass have been considered in the dynamics of robots. The output of controller is wheel's torque and front wheel's steering torque. Moving target dynamics has been considered in a way that it is escaping from invader and the target has holonomics dynamic. To derive the equation of motion, Kane's dynamics procedure has been used. Robots are equipped to sensors for distance assessment, vision angle assessment and also signal receiver antenna. To estimate relative position and variables of other robots'... 

These days, according to increasing requirement to the applications of clean rooms in industries in and within the developing industry of computer, positive indicators that show a real need to a compere comprehensive study and research about the Clean rooms, in oder to predict the distribution and dispersal of the particles. Correct determination of indoor airflow and particle concentration distribution results in new standard development for Clean rooms. As computational fluid dynamics has become a powerful tool for indoor airflow studies, in this research, influence of effective parameters on the flow and concentration distribution in clean rooms has been... 

In order to safe design and optimize performance of industrial systems which work under two phase flow conditions, it’s often needed to categorize flow into different regimes. In present work the experiments of two phase flow were done in a large scale test facility with length of 6m and 5cm diameter. Four main flow regimes were observed in vertical air-water two phase flows at moderate superficial velocities of gas and water: Bubbly, Slug, Churn and Annular. Some image processing techniques were used to extract information from each picture. This information includes number of bubbles or objects, area, perimeter, height and width of objects (second phase). Also a texture feature extraction...