Sharif Digital Repository

Variable speed wind turbines (VSWTs) provide the capability of wide speed operation and independent control of active and reactive power. In contrast to the fixed speed WTs, they have higher efficiency, power quality and controllability. VSWTs are mainly divided in two categories: WTs based on doubly fed induction generator (DFIG) and WTs based on full converter with permanent magnet synchronous generator.
At now, among the different alternatives to obtain VSWTs, DFIGs are the most commonly used. This is because the voltage source converter (VSC) in DFIG has to handle a fraction of the total power under steady state conditions, and thus the size and cost of the converter is reduced.... 

Throughout history, engineers have always been searching for ways to increase the strength-to-weight ratio in the design of engineering structures. Using lattice structures has been a method implemented in different applications to achieve this goal. Herein, two novel hybrid lattice structures are designed, and their compressive quasi-static mechanical behavior is evaluated experimentally and numerically. In one of the designed structures, using dual-phase strengthening, FCC unit cells are incorporated as a reinforcement phase into a BCC matrix. In the multifunctional lattice structure, FCC and BCC unit cells are combined with their central nodes connected. All of the designed structures are... 

Recently, the severe plastic deformation (SPD) is known as one of the most used methods in decreasing the grain size and increasing the strength of metals. In this study, aluminum 1100was subjected toconstrained groove pressing (CGP) at room temperature. The CGPed samples in nanoscale structure, with different CGPed passes were direct rolled and cross-rolled in different rolling strains. Finally, all of the samples were annealed at temperatures of 100, 200 and 300 ° C for 30 min. It was observed that with increasing number of CGP passes and rolling strain the structure became more laminate and finer. With increasing rolling strain, the cross-rolling had greater effect on the microstructure... 

Tipping points occur in diverse systems in various disciplines such as ecology, climate science, economy, sociology, and engineering. Critical thresholds in system parameters or state variables at which a tiny perturbation can lead to a qualitative change in the system exist in many subsystems in complex systems. These thresholds are called tipping points, and these subsystems are called tipping elements. Additionally, many systems with tipping points can be modeled as networks of coupled multistable subsystems. Domino-like tippings are called tipping cascades. Considering that these tipping cascades are primarily unprecedented, it is essential to study the dynamics and control of these... 

The growing requirements for renewable energy production lead to the development of a new series of systems, including wave and tidal energy conversion systems. Due to their sensitivity and the impact of the aggressive marine environment, the selection of the most adequate location for these systems is a major and very important task. Several factors, such as technological limitations, environmental conditions, administrative and logistic conditions, have to be taken into account in order to support the decision for best location. The aim of the present study is to provide an Atlas of IRAN Offshore Renewable Energy Resources (hereafter called ‘the Atlas’) to map out wave and tidal resources... 

Nowadays, with high performance computers and progress in video recorder devices and their related technologies, price of these devices is being balanced and recording the videos is conventional now. Processing of these videos has been a challenge in industry and science. Control and surveillance of places such as airports and roads and reducing their sizes in memory are some of their research area. Usually one of the initial preprocesses of such applications specially the object tracking is background modeling and background subtraction. This preprocess has an essential effect on the other algorithms that process based on these processes’ results. If this section conducted with fewer... 

TiO2 is known as a photocatalyst in near UV-Visible light region with better efficiency compared to other semiconductor photocatalysts. Many attempts have been done to increase the efficiency of this photocatalyst. also, application of 2D carbon nanostructures namely graphene for increasing the photocatalytic activity of TiO2 has shown positive results.
In this research, we first synthesized Graphene Oxide (GO) suspension by exfolation of graphite oxide suspension. then we fabricated TiO2 thin films on glass substrates by so-called sol-gel method. finally we fabricate Graphene Oxide/TiO2 nanowalls composite films as a photocatalyst in visible light. X-ray photoelectron spectroscopy... 

Among probable hazards in chemical industries: vapor cloud explosion (VCE) is one of the worst and most destructive ones. More than half of the major process inci¬dents, according to the statistics, are VCEs. VCE causes the most serious consequences; therefore, it attracts many attentions to itself. Accordingly, plenty of researches have been done for the purpose of protection against VCE effects. All efforts in this field can be categorized in two different main activities; firstly, prescribing safety distances between groups of hazardous equipment and vulnerable areas, secondly, using facilities which reinforce vulnerable areas against explosion blasts. Regardless to which category is... 

Due to the important role of base plates, both in transferring forces from the structure to the foundation, and also in transferring vibrations from soil to the structure, it is necessary to have sufficient knowledge on their behaviour and performance under monotonic and cyclic loading regimes. In fact, the behaviour of the supports of any structure cannot be identified without identifying the behaviour of its base plates. Numerous configurations with/without various types of attachments have been proposed and used for base plates. In this work, altogether six commonly-used types of base plates were studied and their behaviour under monotonic and cyclic loadings was obtained using commercial... 

The fratar model that is one of the most common models of travel distribution has some weak points. Due to its strong tendency to existing distribution and disregarding the zonal characteristics, this model is unable to consider sudden changes in plan on the horizon. In order to identify the variables affecting the distribution of travel, using the behavioral approach is vital. For this purpose, Multinomial Logit model is used for distribution of shopping trips in the city of Shiraz. The city of Shiraz is divided into 156 zones. If all zones be considered as the choice set for each traveler, the results of model won't be efficient. To address this problem, sampling should be done based on...