Sharif Digital Repository

In this study, the nonlinear vibrations of an elastic rotor that is under the elastic support and under the follower force caused by the airflow passing through the rotating plane are investigated. The elastic shaft is modeled by the Timoshenko beam theory, which is connected to a motor through a flexible coupling and the motor increases the rotational speed of the rotor by applying torque. Gibbons’ equations have been used to model the misalignment forces. First, the kinetic energy of the rotating system is calculated nonlinearly to take into account the effect of nonlinear terms due to the rotational inertia of the system, and then the potential energy and The work of external forces on... 

The main objective of this research is to predict the life of a bearing that works in variable speed working condition. In this project, two series of experiments were conducted to investigate the vibration of the bearings. In the first series of experiments, multiple imperfections have been created on parts of the bearing that are susceptible including the inner ring, the outer ring and the balls. The results of this test have been used to study the importance of speed compared to other parameters in increasing the vibration levels of the bearing. In addition, the results of this experiment have been used as inputs to a neural network. This neural network is trained to classify bearing... 

In this research, the main purpose of the controller design is in the second region of operation of a wind turbine, which involves absorbing the maximum energy from the wind. WindPACT 1.5MW turbine has been investigated and the power coefficient of this turbine has been obtained using WT-PERF and FAST softwares. Simulations show that the results of both methods are well matched. Then, using ANFIS, a method for estimating the wind speed is derived from the data obtained by FAST. Inputs to the ANFIS system are the turbine aerodynamic power, rotor speed and blade pitch angle while the output of ANFIS system is the estimated wind speed. The maximum power coefficient of the wind turbine occurs... 

Hyderogels are hydrophilic polymers with three dimensional network structure, due to their high water absoption, their application to life and industry is increasing from day to day, such as tissue engineering, actuators and sensors, drug delivery and therapeutic treatment. In this project, it has been attempted to produce polyacrylamide/alginate double network hydrogels with the use of graphene oxide nanosheets to indicate that it is possible to combine toughness and self-healing in a hydrogel with the opposite nature of each other. To evaluate mechanical properties, uniaxial tensile test and loading-unloading test were used. The results indicate that increase the weight ratio of acrylamide... 

In recent years, planing boats have been used in more exposed areas, for instance as patrol boats, pilot boats, coast guard and small naval vessels. When such a small vessel operating in a rough-water environment, frequently experiences violent motions and vertical acceleration. Even on calm water, porpoising may occur and may be severe as the speed is increased. Operation of the crew, equipments and overall operability of the vessel always suffer from mentioned motions. In the present study, the impact of fixed and controlled interceptors on a planing crafts hydrodynamic and seakeeping quality is investigated through application of an experimental and theoretical methods. Two scaled-down... 

This study seeks to evaluate reliability of wind power density over Khouzestan province using WRF simulations. Based on 10 meter wind speed data extracted from eight synoptic stations over Khouzestan province, two different domains were selected in south and south-west of khouzestan as promising regions with strong wind speeds. WRF model were used to simulate atmospheric data during 2016 and over two selected regions with 2 kilometers grid spacing. Simulated data were verified with comparing to in-situ data via three parameters of RMSE, BIAS and correlation. Results indicate that model configuration had acceptable accuracy in simulating wind speed data. In this study, Monte Carlo... 

Due to increasing air pollution and traffic jams, cities are trying to promote non-motorized modes of travel. Therefore, people are encouraged to take ad-vantages of walking to decrease usage of motor vehicles and to enhance their health. Knowledge about pedestrain behavior helps planning and provision of efficious facilities for walking. To address the issue, it was decided to examine pedestrains behavior in Tehran Bazaar. The vicinity of Tehran's old Bazaar is considered to be one of the populous, important commercial centers of Tehran and one of the most spacious footpaths. Behavior analysis is done in both macroscopic and microscopic levels. In the macroscopic analysis the re-lationship... 

According to development of industry in every field such as nanotechnology and micro electro mechanical system (MEM) fabricating of high speed machining with micro dimension has been expanded. Micro spindles are such a device which is useful in many industries such as air space and electronic field. These machines can work in high speed and production rate with vast variety of features. Their dimensions are in millimeter range. So they can manufacture miniature features. Fabricating and technical science production of a high speed micro spindle with speed of more than 100000 RPM (micro macro milling) is purpose of this project. After to literature review according to science of micro... 

Encompassing an interaction between the phase change material (PCM) and the droplets of a heat transfer fluid, the direct contact (DC) method provides a state-of-the-art solution for the meager melting and solidification rates of PCMs. In the DC procedure, when impinging on the molten PCM pool, droplets evaporate, solidifying the portion of the PCM. For the first time, the impact of single and simultaneous double ethanol droplets, having an average diameter of 2.68 mm, on the molten paraffin wax has been scrutinized exhaustively. Experiments have been carried out through high-speed imaging for various Weber numbers ranging from 179 to 464, pool temperatures from 70 to 95°C, and horizontal... 

Today, Mg and Al as the widely used metals, make a special contribution to automotive, electronics and aerospace industries. Increasing the application of alloys of these metals, has extended the demand for reliable joint between alloys of these two metals. The main problem with the dissimilar joining of A356 alloy and AZ91 alloy is hard and brittle intermetallic compounds formation such as Mg17Al12 and Mg2Si which brings about welding strength reduction. By far, a large number of researches about dissimilar joining of AZ91 alloy and A356 alloy in semi-solid condition have not accomplished. In this method two fragments, one from AZ91 alloy and another from A356 alloy among which was a 2... 

High speed data converters are very often used in telecommunication systems. Since these systems are increasingly used in mobile form reducing the power consumption in these circuits is of great importance. The goal of this project was to design a pipeline 10 bit converter for a sample rate of 40 M sample/s with a power consumption of 20mW for the input level of 1Vp-p and a 1V power supply in 0.13μm CMOS technology. To reach these goals a number of low-power techniques are proposed in various levels of abstraction. In system level, the sampling and feedback capacitors, as well as the stage resolution of the ADC is optimized analytically which leads to simple back-envelope formulas to... 

Measuring the speed and position of the rotating part and using the speed and position information in the closed loop control of electric machines is very important. Various sensors are available for this purpose, including resistive sensors, capacitive sensors, encoders, synchros, resolvers, Halleffect sensors, and etc. Common encoders include optical and magnetic types. There are two main problems in using an encoder as a sensor: determining/maintaining accuracy during change of rotational direction and determining the absolute position. Both of the mentioned challenges have been investigated in the case of optical encoders and some solutions have been provided to overcome them. Although... 

Reservoir simulation, recognition of the past and present reservoir behavior and prediction of its behavior in the future, which forms one of the most important parts of the management of a reservoir. In fact, the reservoir is like a living creature and increasing the accuracy in predicting its behavior requires a precise model. Reservoirs have high physical dimensions that are associated with high physical changes. As a result, a large number of computational cells are needed to simulate the reservoirs, which results in a very large linear equation system. The numerical solution of these systems is very time consuming. Many observed examples indicate that 80 \% of the runtime is included.... 

Fire in Grasslands is one of the most dangerous natural disasters that is uncontrollable at the time of its occurrence and will continue until there is a fundamental change in the conditions of the fire. Fire in Grasslands due to the high density of vegetation can produce a large amount of heat energy in a short time and in a very large area, which alone can cause the spread of fire in Grasslands. Today, numerical studies of fire behaviour and propagation are given more attention than experimental studies due to their lower costs and limitations. In the present study, the numerical simulation of the fire spread with the influence of climate parameters such as humidity, rainfall during fire... 

The objective of this investigation was obtaining sound Friction Stir Welded (FSWed) Commercially Purity Titanium using suitable Tool’s Materials (for Shoulder and Pin) in order to be able to work in high temperature (>1000 ˚C) with great mechanical properties and minimum wear during process. Consequently, different materials and designs for Tool, such as High Speed Steel tool, Tungsten based tool, Tungsten Carbide (WC-Co) based tool and diverse tool geometry and designs like simple design, threaded design, fixed pin and inserted pin (adjustable pin) was used. The results demonstrated that using simple cylindrical WC-Co for pin and Tungsten for shoulder resulted in joints with the best... 

Centrifugal compressors are vastly implemented in the industry due to their higher pressure ratio per stage. So, researches are still going on to improve the performance of these devices. On this way, the current project is defined to perform geometrical optimization in the impeller of a centrifugal compressor using numerical and experimental methods. In this research, the design process of centrifugal compressors is first discussed according to methods and guidelines provided in several references. Then the compressor of the GT4082 turbocharger is redesigned using these theories. It is shown that overall available rules are enough to design an acceptable centrifugal compressor. Experimental... 

This study analyzes determinants of customers’ switching intentions. The context of this study is service area and we have studied customers’ behavior of internet service providers. In this research we focus both on transactional and relational variables. We have tried to clarify the role of consumers’ commitment on their intentions to switch. Drawing from literature and based on previous service switching research we have developed a switching model. This includes two component of customer commitment and the antecedents of commitment. We have developed our hypothesis according to this model and the literature review. The survey was administered to ADSL internet home users. A sample of 130... 

To reduce customer waiting times in various service conditions, admission control and service speedup can be implemented during times of congestion. In a healthcare setting, this may result in a patient being redirected to an alternative treatment facility. Additionally, waiting for patients can have negative impacts on their health and controlling population density can be costly. Implementing these measures may also take too much time or deviate from the ideal treatment. In this thesis, we will evaluate multi-server queuing systems by considering both speed and admission control simultaneously. We will use dynamic programming to determine the optimal control characteristics and calculate... 

In practice, to implement Federated learning on edge networks, devices must repeatedly transmit their trained models to the edge server through wireless links to update the global model; Due to the heterogeneity in the Federated Edge learning system, such as lack of power, some devices may not be able to connect to the base station and reduce the performance of the trained model or, if connected, impose a large delay on the learning process. To overcome the mentioned challenge, we propose a Collaborative Federated learning framework. In this framework, some devices can participate in Federated learning without connecting to the base station; In this way, devices that are not able to... 

The purpose of this research is to provide a method for finding a “good” solution to the network design problem with less computational efforts, faster than the existing conventional methods of solving this problem. Network design problem is the problem of selecting a subset of projects from a set of alternative projects so that to optimize the objective function (e.g., the total travel time in the network) subject to the set of existing constraints (e.g., budget). Due to the combinatorial and non-convex nature of the problem, its solution could be very cumbersome and time-consuming. Various methods have been proposed to solve this problem efficiently, providing good solutions at high...