Sharif Digital Repository

Lateral spreading due to liquefaction and resulting destruction of buildings is important in Iran because of high seismicity and important infrastructure near south and north coasts of Iran. Lateral spreading is vast lateral movement of sloping ground or level ground ending in an opening like river which is caused by earthquake inducedliquefaction. For considering the effects of lateral spreading during design of deep foundations of structures in a susceptible area, one needs to determine the lateral loads on piles under lateral spreading. Present study investigates the behavior of a 3x3 pile group against lateral loads due to lateral spreading with numerical methods using OpenSees software.... 

Results of an advanced suction controlled triaxial test device in an attempt to define the constitutive relationship between suction stress and matric suction (Suction Stress Characteristic Curve, SSCC) for unsaturated sand was presented. The suction stress is a macroscopic stress that incorporates the effects of capillary van der Waals forces cementation, and electrical double-layer repulsion into the definition of effective stress for unsaturated soils. Results of previous studies on silt and clay indicated that variations in the suction stress, during drying path had a non-linear increasing trend with matric suction with greater values upon wetting. However, due to different material... 

Due to an increasing need for refrigeration systems and consequently increasing in electricity usage and greenhouse gases production, using ejector refrigeration systems would be a suitable substitution for conventional cooling systems. Main drawback of ejector refrigeration systems is their low coefficient of performance. The key component to improve the cycle performance is the ejector. Prerequisite of improving ejector performance is an accurate CFD simulation for predicting entrainment ratio. In this study, a two dimensional, axisymmetric, steady state, compressible flow CFD simulation of a supersonic ejector is presented. CFD results are validated with experimental data. Furthermore,... 

Magnesia–Doloma refractories are considered as a mixed product of alkali products i.e. sintered (fused) magnesia and doloma in which 50-80 wt% magnesia is contained. These refractories enjoy some advantages such as high slag resistance corrosion, high-temperature performance, potential for production of pure molten iron and low cost due to abundance of magnesia and doloma resources in access. However, there exist some problems with these refractories that render them unsuitable for some applications. Among these cases, poor resistance of hydration can be cited that may constrain the amount of this refractory in various industrial applications. In the present work, the addition effect of... 

In recent years horizontal Ground Heat Exchangers (GHEs) has attracted a growing interest as heat source/sink for ground source heat pump systems. Horizontal GHEs initial installation costs are lower than the vertical ones; however, they require larger land area and more pipes. Therefore, it is necessary to reduce their required land area and pipe length by improving their thermal performance. In this study, a numerical modal based on 3-D simulation of GHE with computational fluid dynamics methods is developed. The model is used to evaluate the thermal performance and initial installation cost of horizontal GHEs. Four different types of horizontal GHEs: linear, spiral, horizontal and... 

Nowadays by fast growing the population and development of countries, the demand of energy is increasing rapidly. Solar energy is one of the most reliable and environment friendly source of energy. Photovoltaic modules (PV) are such a solar systems that is able to convert solar energy into electrical energy. However, some parameters such as increasing cell temperature and dust accumulation can reduce the PV modules efficiency. Increasing the cell temperature reduce the capability of electrical production of cells and dust accumulation is an obstacle for solar radiation absorption. As a result, in this research tempt to solve these problems by building a new device for PV modules. In this... 

The annual increase in electricity consumption has led to several problems, including greenhouse gas emissions and global warming. Refrigeration systems are one of the main electricity consumers in the world. Ejector refrigeration systems use waste heat from industries or renewable sources such as solar energy to create the cooling effect. One of the main problems with these systems is the inefficiency of the cycle by the change of the ambient conditions including temperature rise. In ejector vapor compression refrigeration cycles, the compressor increases the pressure to an intermediate pressure. and the rest of the pressure increase is provided by the ejector. These systems can provide the... 

Inlet air cooling is a simple and economical method to increase the power output of gas turbines. High-pressure fogging systems and mechanical chillers are two common methods. High water consumption, damage to compressor blades by water droplets, and inefficiency in humid climates are disadvantages of high-pressure fogging systems. Mechanical chillers have high electricity consumption and initial costs. In this research, an earth-to-air heat exchanger (EAHE) is introduced as a new method for inlet air cooling of gas turbines and is technically and economically compared with the two common methods in the long term in the climate of Tehran city. Temperature distribution in the ground is... 

In this study, the micro and nano particles of substituted strontium hexaferrites with nominal composition of SrFe12-xTix/2Znx/2O19 (x=0, 0.5, 1, 1.5, 2 and 2.5) were prepared by a co-precipitaion method. Ferrite-PVA composites (70:30) with thickness of 1.8mm were prepared at 220°C and 50Mpa. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometer (EDS), vibrating sample magnetometer (VSM) and vector network analyzer (VNA) were employed for characterization of synthesized powders and composites. XRD and FTIR results showed that single phase hexaferrite were obtained for almost all of the... 

Named Data Networking (NDN) is a revolutionary architecture for the future Internet. The existence of a large number of unbounded and variable-length names in NDN requires substantial re-engineering of network architecture, especially for name lookup which is key to NDN routers. In this paper, we propose a novel NDN structure – called Fast-Come-Fast-Served (FCFS) – for fast, scalable, and memoryefficientlookup. To the best of our knowledge, this is the first optimized structure that employs Deterministic FiniteAutomaton (DFA) for Longest Prefix Matching (LPM) in NDN. The strengths of arrays and hash tables as core data structures are combined to make FCFS fast and cache-friendly. The NDN... 

During the last few years, utilization of distributed generation (DG) in power systems has been widely increased. This trend has magnified studying the effects and impacts of DG on such systems. One of the benefits of DGs in a power system is loss reduction. If determining DG size and place is done properly, the loss of the network can be minimized. Another way of reducing loss in distribution network is by reconfiguring the network. During the reconfiguration, constraints like being radial, avoiding load isolation as well as voltage/current limitations must be taken into consideration. Taking these constraints into account makes reconfiguration an optimization problem. In this project, the... 

The necessity of electrical energy, high cost of big power plants and high voltage transmission lines and also progressing of restructuring science has lead to the increasing of tendency to use the distributed generation in electrical industry. Among of different types of distributed generations, fuel cell power plants because of many advantages such as high efficiency, low emission, modular structure and ect., have a high potential to be used in power systems. The fuel cells produce electrical energy by chemical reactions. Due to the necessity of having the knowledge related to the chemical reaction which are effective on fuel cell, to study the fuel cell performance, this type of... 

With the increasing penetration of renewable energies as distributed generation (DG) in power systems, technical problems arise in both distribution and transmission system level. Voltage rise is the main barrier for connection of DGs in rural areas, while excessive reactive power demand from transmission system is the major concern for Transmission System Operators (TSO). Here, a centralized control scheme based on the Smart Grid is proposed to reduce the impact on the transmission system voltages and improve its stability, while mitigating the voltage rise issue in the distribution network. Reactive power output of DGs, substation capacitors and tap setting of transmission transformer are... 

Based on codification and implementation of regulations of supporting from development of distributed generation sources, it is expected that in future years, investment in distributed generation scheme will be welcomed by private investors impressively. Under this circumstances, distribution Company will be faced with new chances for improving quality level of their services and optimal management of penalty-reward schemes. Penalty-reward schemes is set by legislator for distribution Company in order to improve their network. One of the pioneer ways is using distributed generators. So first, distribution Companies have to find optimum places for using these generators and in the second step... 

Today, global warming is one of the main concerns of human society. Many factors contribute to global warming and air pollution. Air pollution in the metropolis cities has influenced human life. Vehicles are considered as one of the major sources of air pollution. Vehicle air conditioners bring conform to passengers, but they increase fuel consumption. Increased fuel consumption results in the production of pollutants and air pollution. In this study, the ejector cooling system is proposed as a cooling system of a car air conditioning system, and its performance is studied. To this aim, first, an ejector cooling cycle equivalent to the compression cooling cycle is designed. The ejector is... 

The integration of renewable energy sources introduces several issues including islanding operation. Therefore, Islanding phenomenon should be detected by a fast and reliable islanding detection method. In this thesis an intelligent-based approach is proposed to detect islanding state for Photovoltaic (PV) and Doubly Fed Induction Generator (DFIG) units. Decision tree classification algorithm is chosen as weak classifier and by Adaptive Boosting (AdaBoost), detection accuracy is improved. 16 features are employed to construct feature vectors. Because of intermittency of renewable electricity generation, different states for PV and DFIG generation are assumed. Probable events are simulated... 

Hydrogen can serve as a green alternative to fossil fuels and contribute to improving environmental conditions. In this context, reducing the cost of hydrogen production is of fundamental importance. It is necessary to examine the impact of influential environmental parameters on hydrogen production cost reduction. In this study, a relationship for optimizing hydrogen production in two scenarios, with constant anode pressure and variable cathode pressure, as well as both variable anode and cathode pressures, has been presented. Furthermore, the effect of various parameters, including temperature, pressure, proton exchange membrane thickness, and solar cell efficiency, on hydrogen production... 

Economical strategy of developed countries imposes to improve energy efficiency and a rational renewable energies usage in the buildings. Ground source heat pumps are one of the most important tools in the way moving toward this goal. This study focuses on studying the effect of applying different refrigerants in the direct expansion ground source heat exchangers. In order to compare the performance of the ground source heat pumps using different refrigerants, a specific methodology is presented and implemented. First on this study, the thermal performance of a geothermal borehole filled with both CO2 and a zeotropic mixture of CO2 and R32 (20/80) is studied and the quality, temperature, and... 

The purpose of this study is to identify the False Data Injection (FDI) attack and reconstruct the incorrect data created by FDI in the power system using machine learning algorithms. Unlike conventional power grids, the smart grids due to the increase of smart devices and communication networks to transfer power grid information from one point to another and the need to control and monitor the power grid is an electrical network that is integrated with a communication network (cyber-physical system). A communication network that transmits data between the control center and smart meters increases the threat of cyber-attacks in the power grid. In this study, the aim is to investigate the FDI... 

Nowadays, worm robots are widely designed and manufactured for different applications. The most common applications for these types of robots can be mentioned as maintenance of small pipes and medical purposes in biological vessels such as the lungs, intestines, urethra and blood vessels. The robot must be small, controllable, safe, reliable, energy efficient, and must be able to crawl both, forward and backward. Different worm robots have been developed and manufactured, for different purposes such as, medical and industrial applications. Most of these projects are typically designed with three or more actuators for control of the distance between cells and the clamps.The results of using...