Sharif Digital Repository

Distributed generation (DG) technologies have achieved an intense progress during the last years. One of the appropriate ways to enter a DG system in the electrical network is through the use of microgrids. Because the majority of DG units are connected to the grid with power electronic converters, specific control strategies have been developed for these converters. Control strategies of DGs in microgrid differ in the grid-connected and the islanded states of operation. Changing the control modes from one state to another requires a reliable islanding detection method, and results in unwanted transients. It is, therefore, desirable to devise an integrated control approach for both states.... 

Three-phase voltage source converter (VSC) is vastly utilized in the renewable energy resource and distributed generation (DG) systems interface units due to its high controllability and flexibility. Because of the high nonlinear nature of the system, the gird-connected inverter shows poor performance if the conventional control scheme are used. In this thesis, a new control scheme based on backstepping strategy is presented for control of a grid connected DG systems. The proposed scheme is responsible for regulating the active and reactive power components of the VSC power of the DG system. The VSC of the DG system is connected to a stiff utility grid through an L-type filter. In the first... 

Block shear failure in the parent material is considered as a common potential failure mode in welded connections used in steel structures. However, there is only little research reported on the block shear failure of welded connections under multiaxial loading. Multiaxial loading is defined as loading not parallel or perpendicular to weld lines and in the case of in planar eccentricity results in torsional loads. In this research a nonlinear finite element model is developed to study the effect of connection geometry, weld group configuration, and eccentricity of lap splice connection on block shear capacity. The case studied concerns a 3 milimeter thick structural steel plate (CSA G40.21... 

This thesis has provided an overview of the theoretical justification for the discrete Morse theory، persistent homology، and applications. Once the primary definitions of complexes have been established in the first chapter، we have explored the Discrete morse theory in detail in the second chapter. Then it is used to prove that disconnectivity is an eva- sive feature of graphs. Furthermore، some theorems related to discrete morse theory have been used to reduce the time complexity of ho- mology algorithms. Next chapter، we try to establish the foundation of persistent homology، and then we explore stability theorems of persis- tent homology. Finally، an application chapter has been added،... 

This thesis is concerned with a fundamental problem in computational geometry. This problem inspects covering a space with a set of points provided that each point of the space is visible to at least one point from the selected subset. Applications of these problems are in the areas such as geographic information systems (GIS), robotics,computer graphics and the military.The investigated space is a planar rectangular region which is partitioned into smaller rectangles by connected edges. The objective of this study is to find an optimized corridor; i.e., a connected subset of edges which contains at least one point from each rectangle. For the minimum diameter corridor problem, an exact... 

Patients with a single ventricle disease who have undergone Fontan surgery have always had long-term complications. These complications include pulmonary artery stiffness and decreased ability to exercise. In fact, due to removal of the right ventricle from the circulatory system, blood pressure and pulsatility inflow to total cavopulmonary connection (TCPC) are reduced following this surgery. Creating waves (radial displacement) on the IVC (Inferior Vena Cava) wall can increase pulmonary flow pulsations. The Objective of this study is to test the effect of induced wave amplitude on the pulmonary flow pulsations at the rest condition. Computational fluid dynamic (CFD) simulations were... 

This study considers blood flow in total cavopulmonary connection (TCPC) morphology, which is created in Fontan surgical procedure in patients with single ventricle heart disease. Ordinary process of TCPC operation reduces the pulmonary blood flow pulsatility; because of right ventricle being bypassed. This phenomenon causes a lot of side effects for patients. A cardiac surgeon has suggested that keeping main pulmonary artery (MPA) partially open, would increase pulmonary flow pulsations. MPA gets closed in ordinary TCPC operation. The purpose of current study is to verify the effects of keeping MPA partially open on pulmonary flow pulsations, by means of computational fluid dynamics (CFD).... 

Regarding the numerous casualties and financial losses due to intense earthquakes, the ductility is considered of the main importance in addition to stability, stiffness, and strength criteria of the structure’s connections. In order to enhance the seismic behavior of the structures in such severe earthquakes, design codes for steel structures have suggested special types of connections. Among them, bolted end plate connection is considered a conventional type of connection used for creating ductile semi-rigid connection.In this study, in order to simulate the behavior of this joint, a 3-D finite element model is developed in Abaqus software, in which the inelastic behavior of the materials... 

Fire is one of the permanent threats due to earthquakes, however in spite of the attention drawn towards design and retrofitting of structures in recent years in our country, no effective steps have been taken for examining design methods and control of the structures’ reactions in case of a fire. One of the reasons for this, is lack of observations and data and also lack of a standard for design of structures that are resistant to fire. Since the connections of beams and columns play an important role in performance of the structures, in this research the behavior of a structure having a semi-rigid connection to an end plate has been investigated by performing an experiment on a scaled... 

This thesis presents the development of a Finite Element Model (FEM) for a new type of Beam-Column Semi-Rigid steel connection. This connection consists of a steel semi cylinder connected to a plate and inserted on the top and bottom of the beam connecting it to the column by welding. It seems that changing the geometry of the semi cylinders and their weld lengths can have a great influence on the rigidity or flexibility of the connection. Therefore, meaningful categories of the connection with different semi cylinder geometries and weld lengths have been modeled and investigated by means of a Finite Element Modeling software ABAQUS, and their moment-rotation curves were driven. Also the... 

Today steel tubular systems are used more than before, especially in recent years. A difficulty with this type of systems is making beam to column connections using bolts due to no access to holes of bolts from the inside of tube or hollow circular column. Reverse channel connection is devised and introduced to prevail this problem. Access to holes in this connection is from the inside of channel. In this connection, the web of the channel is connected to steel beam using bolts and the two legs of channel is welded to face of tube column.
This type of connection does include some innovations; not too many researchers work on different versions of this connection. This thesis provides an... 

This study investigates the cyclic experimental behavior of damaged exterior reinforced concrete beam–column joint specimens retrofitted with the proposed technique using steel elements called steel prop and curb. The technique is usable for local and global strengthening of reinforced concrete frames. Four half-scale RC joints were tested under the cyclic loading; two control specimens with the different beam heights were loaded up to their ultimate strength and this was followed by retrofitting of these damaged specimens as new specimens and tested again under the same loading system. This study indicate the importance of some parameters such as friction , jacket place , thickness of plate... 

Steel structures are one of the most common structures in the world. One of the main parts of these structures is the connections, which are divided into three main categories of fixed, semi-rigid and joints, according to
the different criteria provided in the guidelines and codes. Perhaps the main challenge facing civil engineers has been designing efficient connections against lateral loads (seismic loads, wind loads). This issue has received more and more attention from designers due to the poor performance of the fasteners against lateral loads. Investigating and evaluating semi-rigid connections as one of the main part of steel structures against various loads, especially lateral... 

Offshore platforms are the most important and enormous wealth of each country that these structures are in situation thatthelikelihoodof damageinhigh. With considering this pointthatplatformsaresubjected to oscillatinglateralloads, so the occurrenceand growth offatigue crack sinthe misvery common. These cracks are always seen in jacket connections, cause these connections are bearing large forces and have massive welding and the presence ofresidualstresses. The fatigue crack caused negligible change in stiffness of connections and in consequence insignificant change in stiffness of structure; So for this reason, they are difficult to detect in global methods. Fiber optic sensors and... 

Recently, corrugated steel plate shear walls (CSPSWs) have been shown to be an efficient lateral force resisting system for building structures. Corrugated plates have higher out-of-plane stiffness and improved buckling stability in comparison with flat plates which result in improved hysteretic behavior. The application of CSPSWs in tall buildings requires a wide range of thicknesses for the infill plates. Yet, the available range of thicknesses of corrugated plates is limited because of the restrictions associated with the process of cold forming. One solution to this problem is to use two corrugated plates as an infill plate. In this research, the cyclic performance of double corrugated... 

Base plates as the connecting components of steel structures to their foundations, have a crucial role in the behavior of these structures. In order to limit the thickness of base plates hence their cost within reasonable values, various types of attachments (stiffeners) are normally added to them. In this project 6 different configurations, Models, for the base plate and its attachments were considered and studied through finite element analysis. Each Model was studied under the combination of biaxial moments and a range of compressive loads including 0, 0.05 P/Py, 0.10 P/Py and 0.15 P/Py, where Py is the plastic load of the column. The moment-rotation curves of all models under various... 

Occurrence of earthquakes constantly has and still causes damage, human casualties and financial loss around the globe. Therefore finding a solution which enables structures to withstand destructive earthquakes while sustaining the least possible damage to their primary elements, would prove invaluable. In conventional connections of moment-resisting frames, dissipation of seismic energy is accomplished by development of plastic deformations at pre-determined hinge locations on beam and columns, which means damage to these elements is deemed both reasonable and acceptable. However, recently “damage avoidance” principle has recieved close attention, where non-linear behaviour manifests itself... 

A special steel beam-to-column connection, named Khor-jini, is commonly used for steel framing system in Iran. In this system, two continuous beams are passed next to the columns and are connected to the column side using seated brackets.This type of connection has been common in Iran from the late past. Unfortunately, the seismic behavior of Khorjini frames had not been sufficiently studied prior to Manjil Earthquake of 1990. Due to very large damages which occurred in steel structures especially in connections during the said earthquake, the seismic behavior of this type of connection was studied and some of its weak points were recognized.In this study non-linear... 

The purpose of this research is to study the behavior of conventional and retrofitted Khorjini connections. Thus the software ABAQUS 6.11 was used to fabricate the FEM models of the connections with experimental prototypes. In analytical studies, 21 specimens with different size of the connection components were analyzed. True stress–strain curves for steel and weld materials were used and damage initiation and revolution were considered in the weld material. Also cracking of the welds were considered by a micromechanical method. Behavioral characteristics of the conventional connections are specified and appropriate relations are suggested, using Stability equations of the connection... 

The purpose of this research is to study the behavior of some kind of conventional and retrofitted Khorjini connections, such as stress and strain concentration and eventually strain-jumping phenomenon. Thus the software ABAQUS 2019 was used to fabricate the FEM models of the connections with experimental prototypes. In analytical studies, 21 specimens with different sizes of the connection components were analyzed. True stress-strain curves for steel and weld materials were used and damage initiation and revolution were considered in the weld material. Also cracking of the welds was considered by a micromechanical method. The main defects of the connection are severe initial stiffness...