Sharif Digital Repository

Performance-based design (PBD) has been accepted as one of the most reliable design methods in the past few decades. PBD can overcome inherent deficiencies associated with force-based design (FBD) and has advantages over this traditional method. Various PBD methods have been developed, which Displacement-based design (DBD) has been considered as one of the effective design approaches of the PBD method. In this study, the Displacement coefficient method (DCM) is developed for stub-type integral abutment bridges (IABs). For this purpose, two coefficients are proposed to determine the target displacement of these types of bridges. Validation of this method by nonlinear time-history analysis... 

Multilevel converters are considered recently as one of the industrial solutions for high-power and power quality demanding applications. Casacade H-Bridge (CHB) converter is one of the well known topologies among multilevel converters. CHB converter is characterized by its high modularity allowing its power to be easily increased. Modularity also allows any faulty cell to be isolated, so the load can be fed by the remaining operative cells, which leads to an unbalanced output voltage of the CHB converter. To avoid the unbalanced operation, recently a solution based on modifying the phase and the magnitude of the voltage refereces has been proposed. This thesis presents a method to control... 

In this research the appilication of a new method named Endurance Time (ET) analysis in seismic analysis of multi span bridges in linear and nonlinear ranges is investigated. Endurance Time is a time history based method of seismic analysis. In this method structure is subjected to an intensifying predefined acceleration function and different damage indices of the structure are evaluated through analysis time. The Endurance Time criterion and the Endurance Time acceleration functions have been generated in previous researchs of ET group. Using 7 earthquake records which are selected from hundred ones of PEER database based on FEMA p695 recommendations, several scaling methods are used to... 

costs of construction of a structure include: initial construction cost, maintanance cost, seismic risk cost and etc., that in this investigation,the seismic risk of multi-span conc. & steel bridges has been compared. the seismic damage is converted to equivalent finincial value by the concept of life-cycle cost, and then is compared with initial construction cost of structure.in this method, assessment of seismic damage based on structure response, in different earthquake intensity and by damage state concept is done. ET method has been used for predicting response of models.in this investigation two conc. & steel models, with similar geometrical specification and different design results,... 

The three-phase Dual Active Bridge DC-DC converter, by virtue of its various advantages, has been widely used in numerous industrial and sensitive applications. However, this converter includes a large number of power switching devices, which are the most fragile components in Power Electronics, and therefore, can pose a threat to appropriateness of the converter for such applications. Accordingly, introducing a fault-tolerant scheme for this converter is necessary, in order to meet the demands of high reliability and service continuity in aforementioned applications. In this thesis, firstly, the converter is studied during normal operation as well as under switch open-circuit fault, and the... 

Gravity drainage is the control mechanism of oil production from fracture reservoirs. The transfer of oil from the upper blocks to the lower blocks occurs through a capillary continuity mechanism or reinfiltration. One of the conditions for capillary continuity, which plays an important role in increasing oil recovery, is the formation of a liquid bridge in the fractures between the blocks. Therefore, quantitative analysis of the critical fracture aperture for the formation and stability of liquid bridges and the formation, growth and stability of flowing liquid droplets from the top block surface are still challenging and important topic in the study of fracture reservoirs. In this study,... 

Liquid flow between two porous blocks in fractured reservoirs can occur through capillary continuity or re-imbibition. Studies have shown that capillary continuity via liquid bridges formed in horizontal fracture increases oil recovery from reservoirs. The critical fracture apertures for stability of liquid bridges, shape of curvature and fracture capillary pressure for prediction of fractured reservoir performance remain as controversial topics. Experimental results have shown that critical fracture aperture is a function of surface wettability and critical Bond number. Capillary pressure of fracture might be a positive or negative value caused by liquid bridges. The best method for... 

Due to large range searches (there are various alignments between two points) as well as the complex and non-linear cost functions and a variety of geometric constraints, the problem of optimal railway alignment is known as a difficult problem. For this reason, choosing an alignment between two points is usually done based on a limited number of alignments put forward by experts. In recent years, the study of the railway alignment optimization raised again due to the importance of optimization and introduction of various algorithms and their progress in solving various problems. It is expected that applying metaheuristic optimization algorithms, such as methods based on Swarm intelligence... 

The subject of control and stabilization of dc-dc series resonant converter (SRC) is still a challenge in power electronics. The conventional controller design and stability analysis for this converter are based on the model which is derived using the sinusoidal approximation and averaging followed by linearization about an operating point. This model is not applicable to a SRC that operates below resonance especially in discontinuous conduction mode (DCM) because the sinusoidal approximation is no longer acceptable. However, a SRC may be purposely designed to operate in DCM. Therefore, it is essential to investigate the stability analysis and controller design using a more sophisticated... 

It is widely accepted that under reservoir conditions there exists some degree of block-to-block interaction that may lead to capillary continuity. The formation of liquid bridges causing capillary continuity between blocks will significantly affect the ultimate oil recovery. However, accurate modeling of the growth and detachment of traveling liquid bridges which causes capillary continuity between blocks remains a controversial topic. In this work the generalized continuity and momentum equations along with fracture capillary pressure are combined to develop a mechanistic model for formation of traveling liquid bridges between blocks. Firoozabadi and Ishimoto (1994) model is considered for... 

The purpose of this research is to evaluate skew integral abutment bridges. A bridge with an integral abutment bridge system is a type of bridge in which the expansion joint is removed so the connection between the abutment and the superstructure is rigid. Therefore, the superstructure and the substructure are integrated with each other and both participate in the lateral load of the structure under seismic or thermal forces. One of the important challenges in this type of bridges is the lack of analysis, tests and limited three-dimensional modeling. According to this, the understanding of the behavior of skew integral abutment bridges and the effects of soil-structure interaction in these... 

With development of power electronic science and with the existence of different power electronic converters in this field, the need for improving their operation and the fault detection methods of these converters, the need for simulation and test of them is strong felt. However, experimental constrain such as damage risks, reliability, costs, and so on obviate the need for making the converter and the need for testing it and its controller. Accordingly, we do the testing on a special platform for Real-Time simulation.Control/protection platform needs to be tested and its functionality should be verified prior to installation and commissioning.Testing in theReal-Time simulator environment... 

This thesis illustrates the typical seismic retrofitting of bridges using a model governing transverse seismic response of retrofitted bridges by simplified analytical models of the end diaphragms based on the fundamental dynamic concept as well as previous research works. For three types of ductile diaphragm devices such as Eccentrically Braced Frames (EBF), Triangular-plate Added Damping and Stiffness Devices (TADAS) and Chevron Knee Bracing (CKB)and Shear Panel System(SPS), finite element nonlinear analytical models are developed in separate flexural and shear yielding modes, and the capability of the proposed finite element models is ascertained.The IDA (Incremental Dynamic Analyses) are... 

Wireless power transfer provides many medical applications. Recently, power electronic devices are available with high power transmission capability at higher frequencies. This makes it possible to transfer wireless power with considerable amount of power. Due to the reductions of battery size and cost with using wireless power transfer system, this technology is introduced as one of the most interesting topics among researchers. There are obstacles in front of the progressing wireless power transfer applications. Lateral misalignment, load variations, component uncertainties in value are common in wireless power transfer applications. In order to bring this application in large scales, all... 

Bridge is one of the most important structure that are used in urban transportation system. In recent decade, international standards and codes have introduced “Performance Based Design” for structure design criteria. Large and complex dynamic and time history analyzes are obstacles against this method; especially in finding optimum design that requires repeated analyzes. In this research, application of Endurance Time (ET) method in seismic design of urban concrete bridges has been evaluated and value based design of them has been presented. In ET method, seismic performance of structures under artificial intensifying accelerograms is investigated. Performance of structure in... 

Cold plasma due to its special properties has many applications in the microelectronics industry. At the beginning of this study, a few examples of widely used plasmas and the requirements for driving their power sources have been investigated. To generate and characterize plasma, various topologies of DC power supply construction, including high-voltage low-current power supplies called multipliers and low-voltage high-voltage power supplies called converters, have been reviewed and compared.Circuit for pulse generating for plasma application has also been proposed and investigated. In the simulation section, after introducing, reviewing, and compareing the common types of simulators, the... 

In recent years, due to the economical concerns in the structural design, many researches are devoted to introduce new frameworks for optimization of the construction cost as well as maintenance and rehabilitation costs in the life time. The bridges are the most crucial components of the transportation networks and their appropriate performances assures the flow in the transportation network. Hence, the reliability and response of such infrastructures especially in the emergency conditions and the state of servicibality after the hazards like earthquake play a key role in the social life. So far the design procedure of such infrastructures are only limited to the serviceability conditions as... 

Because of environmental problems of fossil fuel energies and the rise in petroleum products, the tendencies to the renewable sources like wind power and solar power have been increased. In some particular applications like electric vehicles, satellites power system and all stand-alone unites that are using solar and wind powers are the only solutions. On the other hand, because of intermittent behavior of renewable sources, use of back-up supplies e.g. batteries are necessary to make a balance in power consumptions and productions. To interface between different ports some independent two port converters are used in traditional techniques. Multiport converters, used in... 

Purpose of this research is evaluation of response modification factor for integral abutment bridges in longitudinal direction in which substructure and superstructure both act as a unit system in resisting of lateral loads and no expansion joints are used in them. One of the most important challenges in design of IABs, is lack of response modification factor for their seismic design in longitudinal direction. Another challenge in these bridges, is modeling of soil-bridge structure interaction that affects not only abutment and piles’ seismic performance, but deck performance too. The other challenge is lack of adequate knowledge about their behavior and seismic performance which is of great...