Sharif Digital Repository

The present research deals with the effect of steam injection to gas turbine engines. First, a comparison is made across the possible positions in the gas turbine for steam injection. Commercial software is used to investigate the pros and cons. Second, the investigation is focused on an industrial 4 MW gas turbine engine. Classical cycle and sensitivity analysis are performed and the operating envelope of the gas turbine engine with steam injection at various operating states as well as different environmental conditions is determined. Finally, a simulator based on Matlab Simulink is developed to examine the impact of different design and thermodynamic conditions of steam injection to the... 

In the study of supersonic air intakes, two important issues including performance and stability are considered. In these types of intakes, when inlet mass flow rate is reduced to a specified amount, a self-sustained instability called Buzz phenomenon occurs. During this phenomenon, shocks and expansion waves oscillate ahead of the intake that will degrade the performance considerably due to the periodic pressure fluctuations inside the intake. In the current study, a supersonic axisymmetric air intake with mixed compression which has designed for a free stream Mach number of 2.0 has been tested were conducted for free stream Mach numbers of 1.8, 2.0, and 2.2, and the results were analyzed... 

By increasing speed gap between microprocessors and off-chip Last Level Cache, Optimization in Last Level Cache makes improvement in system performance. With development of new generation of multi-core processors and sharing LLC between these cores, the so called issue of Memory Wall has caused an incremental effect of LLC on system performance. There are three approaches to use this memory more efficiently:
1. Increasing cache capacity
2. Making cache hierarchical and adding different layers to hierarchy
3. Improvement of replacement algorithms in cache memory
The first approach has not been used in regard with limitation of technology and growth of access time due to... 

Due to the operation of proton exchange membrane fuel cell (PEMFC), temperature will rise because of the electrochemical reactions and control of temperature is one of the most important sections that has influence on the performance of the fuel cell. In this study three alternative for cooling and controlling the temperature situation is proposed and compared. the experimental setup consists of the simulated fuel cell that produce heat just like PEMFC and number of thermosyphon miniature heat pipes for evoke the heat and three types of condenser that makes three different scenario for this cooling setup. Free convection, force convection using Fan and force convection using circulating... 

An extensive wind tunnel tests were conducted on an axisymmetric supersonic inlet at free stream Mach numbers from 1.8 to 2.2, and at different values of mass flow rates. For each test, pressure distributions over the inlet spike was measured and the flow was visualized by means of the shadowgraph system and a high speed camera to obtain main performance characteristics of the inlet during its stable and unstable operations. As the Mach number is increased the pressure recovery is reduced, but maximum value of the mass flow rate is increased. The results of the stable operation of the inlet showed that, variations of the mass flow affects the surface pressure over the entire surface of the... 

The purpose of this research is compare some indicators of size, performance and productivity between exporter and non-exporter plants. For this purpose and, to answer questions of research we use from the industrial plants dataset (1382_1390). We obtain some stylized facts from the dataset then test evidence from data with econometric methods. In this dataset there are information about property, management, sales (domestic/foreign), inputs (domestic/foreign) and information about labor force, capital, investment of plant and many other variety information about plant. The results of my research show that always exporter in most measures of performance, size and productivity advantages... 

Gas turbines and centrifugal compressors are the preferred means of compressing the gas in pipeline systems. Both gas turbines and centrifugal compressors exhibit performance characteristics that depend on the operating point imposed on them by the pipeline operation. Simulation of gas turbine-driven centrifugal compressors is necessary for a variety of applications in the general area of pipeline simulation. This research focuses on modeling of twin shaft gas turbine dynamic and steady state performance. For this purpose, it was necessary to evaluate the thermodynamic working process of the gas turbine by using an in-house computer code. At design point, the calculations are solely based on... 

Today, we have witnessed many changes in computer science. Rapid and exponential growth of data volumes, increasing a variety of data structures and forms, increasing data generation ratio are some important revolutions in our digital world. Because of these changes, our traditional computing models and processing methods cannot solve new big and sophisticate problems. Big data concepts and big data processing methods come to help us for solving these problems. A lot of parallel and distributed processing platforms built for the applications execution on a huge volume of data. Apache spark and Hadoop are two powerful platforms that each has some advantage and disadvantage. With growth... 

Morphing has traditionally been referred to geometric changes made to an aircraft parts and components to enhance its performance or stability. Though, the morphing concept has today developed to a broader scale and covers more than pure configuration or geometric changes. Due to importance and increasing role of HALE aircrafts in reconnaissance missions, their morphing has been recently focused by researchers. Of course, aside from its potential benefits, utility of morphing technology will increase aircraft system complexities and weight that need to be studied and compromised in design process. The present work studies optimal morphing of a HALE UAV by simultaneous analysis of... 

Dynamic Random Access Memory (DRAM) has been the leading main memory technology during the last four decades. In deep sub-micron regime, however, scaling DRAM comes with several challenges caused by charge leakage and imprecise charge placement. Phase Change Memory (PCM) technology is known as one of the most promising technologies to replace DRAM. Compared to competitive non-volatile memories, PCM benefits from best attributes of fast random access, negligible leakage energy, superior scalability, high density, and operating in both Single-level Cell (SLC) and Multi-level Cell (MLC) storage levels without imposing large storage overhead. Unfortunately, density advantage of MLC PCM devices... 

Intrusion detection systems’ test and evaluation is an active research area on which many researchers have been working for years. A complete and comprehensive test methodology that can be applied in reasonable time and cost is important and useful both to evaluate a newly designed system and to compare two or more existing systems to select an appropriate system for a particular network. In this research, we first determine the critical features of an IDS and then inspect methods and effective parameters that may influence the test process and propose a method for testing intrusion detection systems. In the proposed test methodology we only examine critical features which lake of them cause... 

The use of raed cache of hard disk or solid state drives has a magnificent effect on their performance, power consumption, and their endurance. However, one of the main problems of their read cache is its low hit ratio. Thus, the read cache must be used more efficiently. Based on previous studies, nearly all of the blocks which are brought to the read cache are zero-reuse or dead-on-arrival, which means that after the blocks enter to the read cache, they are not accessed until they are evicted. Thus, a large portion of the disk read cache is nearly unused because of these dead blocks. In this thesis, we will design a disk read cache which does not allow to the dead blocks to enter the... 

Many processes and real world systems indicate nonlinear behavior and operate either naturally in multiple regions or in a wide range of operation space. Modelling and control of these systems by nonlinear methods needs to have a deep insight. Furthermore, the nonlinear methods leads to complexity issues. To overcome these problems, multi-model methods are introduced which consist of two steps, decomposition and combination. In decomposition step, the complex system is divided into a set of simple models; in the combination step, the behavior of local models are combined. How to decompose to local models and how to combine them are two main questions in this area which not answered... 

Nowadays, the use of redundancy components on chips is the best method for replacing defective components on chip. This method improves yield parameter and thus reduces the manufacturing cost of a chip. However, in most of yield improvement methods, redundancy is used when the main components of a chip are defective, which is called cold redundancy. In this project, the manufacturing cost and yield parameters of chips, when using hot redundancy in SIMT processors is investigated. In the case of occurring defect on the chip, the hot redundant components are used for improving yield. Otherwise, they are used in order to improve the performance of chip. In this project, we examine systems,... 

The purpose of this research is to investigate the impact of human capital on the performance of startups in Iran so that its findings can be used to guide the startups and companies, policymakers, and entrepreneurs. According to a study by Aguin andcolleagues. (2009), the establishment of new firms through entrepreneurial activities can increase national economic growth, creativity and productivity at the national level. Joseph, in 1995, stated in an article what has been pointed out by some researchers in the field of entrepreneurship in developing countries, Programs and strategies that succeed in a country will not necessarily succeed in another country, due to cultural and governmental... 

Software Defined Networking (SDN) is an emerging paradigm which makes the network programmable by separating the control plane from data plane and makes both planes to work independently. There is a centralized controller and a programmable data plane in these networks architecture and forwarding data packets is realized by programming the data plane via an open interface called OpenFlow. OpenFlow is a communication protocol between control and data planes. The centralized architecture of these networks provides a global view of the underlying network to upper applications and brings numerous advantages such as routing, traffic engineering and QoS control. Despite these advantages there are... 

The increasing gap between performance of Hard Disk Drives (HDDs) and processors has made storage subsystem as the performance bottleneck of computer systems. Solid-State Drives (SSDs) due to having no mechanical parts provide higher performance compared to HDDs. However, the high price of SSDs compared to HDDs prevents them from replacing HDDs. Employing SSDs as a caching layer for HDDs is a cost-efficient solution for designing high-performance storage subsystems. Previous studies on SSD caching neglected to simultaneously consider performance, endurance, and reliability in their architectures. In this thesis, Three-level I/O Cache Architecture (TICA) is proposed, which tries to improve... 

Non-Volatile Memories (NVMs) are emerging storage devices with promising characteristics such as low static power consumption, high performance, and non-volatile property to keep the stored data in the absence of power supply. Despite such interesting characteristics, NVMs suffer from high dynamic power consumption and limited lifetime. These limitations prevent NVMs from directly replacing the existing storage devices without any refinement in the architecture of computer systems. In this dissertation, we first investigate the characteristics of emerging NVMs and offer effective architectures to improve the efficiency of computer systems at the Operating System (OS) level. The main aim of... 

With the rise of the concept of “Big Data”, both data volumes and data processing time increased, imposing the need for new methods of processing and computation of said data.Analytical and computational methods in Machine Learning are some of the most important applications of Big Data processing. There exist many methods of data analysis in the Machine Learning field, each requiring extensive processing on Big Data. One of the methods for working with Big Data is Distributed Systems. MapReduce is one of the most popular methods distributed computation by increasing the ease and speed of distributed processing of big data. But a number of bottlenecks have been discovered in MapReduce which... 

Data Prefetcher is a central component in most processors. Different methods have been proposed with varying degrees of complexity and effectiveness. Recent research revisits pairwise-correlating data prefetching due to its extremely low overhead. Pairwise-correlating data prefetching, however, cannot accurately detect where data streams end. As a result, pairwise-correlating data prefetchers either expose low accuracy or they lose timeliness when they are performing multi degree prefetching. In this work, we propose a novel technique to detect where data streams end and hence, control the multi-degree prefetching in the context of pairwise-correlated prefetchers. The key idea is to have a...