Sharif Digital Repository

Nowadays, information gathering based on wireless sensor network (WSN) has formed various applications and it also seems to be spreading more in future. Wireless sensor network, is a network composed of multiple nodes, without any infrastructure, each having one or more sensors, wireless communications unit, processing unit, memory, and power supply. Memory capacity, computation power, and power supply are usually considered as valuable resources and limited in nodes. Most of sensor nodes are located in a dense mode and they are susceptible to failure. Therefore network topology may vary dynamically. A sensor network can support real-time communications independent of its type of structure... 

Recent advances in VLSI technologies have enabled current silicon dies to accommodate billions of transistors in the design of very complex System-on-Chips (SoCs). To address the resulting complexity, Network-on-Chips (NoCs) have emerged as a paradigm to design scalable communication architecture to connect the processing cores of an SoC. However, smaller feature sizes, lower voltage levels and higher frequencies in Deep Sub-Micron (DSM) technologies make NoCs highly susceptible to transient faults, e.g., crosstalks, particle strikes, electro-magnetic interferences, and power supply disturbances. Single Event Upsets (SEUs) caused by high energy particle strikes as well as crosstalks are the... 

In the presented dissertation an analytical model is developed for the air gap flux density and the cogging torque in the axial flux surface-mounted PM machines. The slotting effect is taken into account in the magnetic flux distribution.The model is derived from solving the 2D Poisson' equation in the slotted air gap. To simplify the solution process, the concept of the uniqueness theorem is used to replace the slotted air gap by a slotless one and some surface current distribution. In addition, the separation of variables method is applied to the analytical solution of the Poisson equation. However, the proposed 2D analytical model is developed for the quasi 3D model by the well-known... 

Steam-Assisted Gravity Drainage (SAGD) is one of the best and the most effective methods of enhanced oil recovery (EOR) which is used in the production from Heavy Oil Reservoirs which constitute large amount of oil throughout the globe. In a typical process of SAGD, steam is injected into a horizontal well and the oil is produced several meters deeper in the ground. In order to increase the Recovery of this process, it is better to review on the Pre-heating methods around the injecting and producing wells. Pre-heating is important when the viscosity of the oil is large enough to prevent oil from any motion at the beginning of the SADG operation, and makes it necessary to to use a Pre-heating... 

Many structural systems may experience some local damage during their lifetime. If the local damage is not identified timely, it may lead to undesirable consequences. Vibration-based damage detection techniques of structures are global methods and are based on the assumption that damage alters both the physical properties, such as mass, stiffness and damping, as well as the dynamic properties of the structures. It is therefore feasible to utilize measured dynamic quantities, such as time histories, frequency response functions (FRFs) and modal parameters, from structural vibration to detect damage. Damage identification based on vibration characteristics is essentially a form of pattern... 

Today, position sensors are inseparable parts of engineering systems. Encoders and resolvers are the most common types of position sensors that are widely used in industries. Due to low price and high accuracy, encoders are the first choice of engineers. Yet, their performance deteriorates under harsh conditions, namely wide temperature range operation, intense vibration and polluted environments. On the contrary, resolvers are rigid and robust which make them resistant to polluted environments.According to principle of operation, resolvers are divided to two main types: variable reluctance (VR) and wound-rotor (WR). Researches has shown that wound rotor resolvers have better performance... 

In recent years applying solid state drives in data centers, cloud computing infrastructures and commercial servers have had a considerable growth. Low power consumption, high throughput and resistance to physical damages are some of the advantages of SSDs over HDDs. In recent works the necessity of using an interconnection network as a communication subcomponent between memory flash chips and disk controller is described. Disk mechanisms (mapping, wear-leveling and garbage collection) influence on throughput of the network. Based on this fact in this research an analytical model is provided considering disk mechanisms, flash chip structure and traffic characteristics. The error of the model... 

Shot peening is a cold-working process commonly used in industry to improve the fatigue performance, stress corrosion resistance and surface nano-crystallization of metallic parts. This process extends fatigue life via two mechanisms: Preventing the crack growth due to compressive residual stresses and, preventing the crack initiation because of increased material hardness. These mechanisms are the results of the bombardment of the component's surface with small spherical particles. In this research, an analytical model is developed for estimating the residual stress distribution induced by shot peening process. The modifications of the developed analytical model are related to... 

In cloud computing services, high availability is one of the most quality requirements that it is necessary to maintain customer confidence. This requires various fault tolerance mechanisms for coping with software and hardware failures.In this thesis, after reviewing previous research, eight different scenarios was designed for availability evaluation of redundant openstack private clouds, represented by RBDs and Markov chains, hierarchically assembled.Based on the availability and downtime results obtained from the scenarios and cost consideration of company, best architecture for openstack is implemented.For real world modeling, we tried to collect and analyze the hardware and... 

Broadcasting in wireless ad hoc networks serves many important tasks such as data dissemination and route establishment in which one node sends its data to all other network nodes. The most popular form of broadcasting adopted by many ad-hoc protocols is flooding. In flooding, each node receiving a packet from a neighboring node rebroadcasts it exactly once. Wide adoption of flooding for broadcasting traffic is mainly due to its simplicity. The importance of performance analysis of flooding lies on its aforementioned popularity. The parameters of interest in analysis of flooding are network coverage, energy consumption and broadcast throughput while network coverage is the average percentage... 

Free fall gravity drainage is one of the most effective mechanisms of producing the oil from the matrix blocks in the gas invaded zone of the naturally fractured reservoirs. Although several analytical models have been proposed to characterize this mechanism in a matrix block, but these models suffer from the practical or theoretical viewpoints. In this study, a new analytical model was presented to predict the oil production rate versus time from a homogeneous matrix block under free fall gravity drainage mechanism. The model was developed by considering the balance between involved forces in the gas-oil gravity drainage process. By simplifying the equation derived from the momentum... 

Use of nano-scale VLSI technologies in the fabrication of System-on-Chips (SoCs) makes reliability as one of the major issues in the design and implementation of these products. SoCs are susceptible to several fault sources such as crosstalks, cosmic particle strikes, electromagnetic interferences, and power supply disturbances. Among the mentioned fault sources, crosstalks have the major contribution in threatening the reliability of SoCs. This thesis addresses the modeling and mitigation of crosstalk faults. In this regard, two analytical models and three crosstalk reduction methods have been introduced. The proposed analytical models, which have been introduced in the fourth chapter of... 

Resolvers, due to their robust structure, are widely used in automation systems. Among the types of resolvers, the accuracy of the Wound Rotor (WR) resolver in the occurrence of common mechanical errors is higher than other types of resolvers. therefore, in this thesis, an AFWRR is studied to improve the performance. Increasing the number of poles in WR resolvers is a good solution for increasing the accuracy of these electromagnetic position sensors. However, high-speed WR resolvers due to employing fractional slot windings suffer from rich sub-harmonics in the induced voltages. A common solution for suppressing the undesirable sub-harmonics is using multi-layer winding with appropriate... 

Linear motors are mostly used in industrial applications and linear position sensors are one of the main components of their motion-control systems. The most common position sensors are optical encoders and resolvers. The optical encoders are not suitable for use in high temperature and high-vibration environments. In addition, their mechanical installation is difficult. In contrast, the resolvers are capable of generating absolute position signals with high precision, and low cost. Resolvers can be used in the polluted environments with the wide range of frequency, temperature and vibration. Among different linear sensors, linear resolvers are appropriate choice for harsh environments.... 

Investigation of possible vibratory responses of dynamical systems around their stable equilibria is an essential step which must be taken before their both design and application. The attained results of such a study can largely help to prevent instability in closed-loop stabilized systems by avoiding excitation of the system in the neighborhood of its resonance. In this paper, nonlinear oscillations of a Rotary Inverted Pendulum (RIP) enjoying a full-state feedback controller is investigated. Lagrange’s equations are employed to derive an accurate 2-DoF mathematical model whose parameters are extracted by both measurement and 3D modeling of the real system components. The perturbative... 

The soil-water retention curves (SWRC) is an unsaturated soil mechanics hydro chemical state surface, which expresses the relationship between the soil suction and water content. The soil-water retention curve could describe the water adsorption and desorption process that happened in soils. The difference between the desorption or drying retention curve and the adsorption or wetting retention curves in a specific soil specimen indicates the hydraulic hysteresis phenomenon. Generally, the amount of water remaining in the drying process is greater than the amount of water adsorbed in the wetting process at a certain amount of suction. Suction due to the combined effects of capillary and... 

Some types of composite material used in aerospace industry make with braiding technology and Some type of fabric textilled with braiding machine, one of them is 2-D Triaxial braid fabrics.In this thesis, generated new an analytical model for predicted mechanical properties of 2-D Triaxial braid composites. This can prediceted equal elastic modulus and equal shear modulus and equal passion ratio for this composites and this model can predicetd volume fraction of fibers and resin  

Vertical ground-coupled heat pumps due to using a renewable energy stored in the ground and being away from ambient temperature fluctuations have a good coefficient of performance and very low pollution. Despite these advantages, these systems have not gained a pervasive position in the field of heating/cooling systems due to their high initial cost. Despite these advantages, these systems have not gained a pervasive position among communities due to their high initial cost. In the present project, a comprehensive study has been conducted to investigate the effect of using zeotropic refrigerant mixtures on the performance of vertical ground-coupled heat pumps and reducing its initial costs.... 

With the recent developments in power electronics and electrical drives, there is a need for precise position sensors today more than ever. Having high precision and high reliability in harsh environments, resolvers are the most preferred position sensors among other types of prevalent position detectors. In order to control linear machines, which are widely used in different industries, linear resolvers are employed. This project aims to propose a structure for tubular variable reluctance resolvers, formulate an analytical model for and optimize the proposed structure. In addition to having an acceptable precision, the proposed model should be less time-consuming compared with finite... 

Electrical machines represent an important research area in electrical engineering with numerous industrial applications. Multiphase induction machines are considered as the new generation of electrical machines in industrial applications because of their structure, robustness, simplicity, reasonable cost, long lifetime, and high reliability. A solution in the way of improving induction machine performances is using concentrated windings because they have many advantages such as short non-overlapping end turns, high fault-tolerant capabilities, and easy manufacturing. The main drawback of concentrated windings is its low-quality air gap flux density which significantly deteriorates induction...