Sharif Digital Repository

It is several decades that the effect of soil-structure interaction (SSI) has been known to engineers. Many methods have been developed to estimate this effect, but modal analysis of soil-structure systems is one of the most popular techniques due to its simplicity and better insight. Due to this reasons, modal analysis found its place in codes and provisions such as NEHRP. Presence of soil beneath the structure not only would alter the natural periods and damping ratio of structure but also would impose some new vibration modes to the system due to soil’s degrees of freedom. Consequently, response of structure is a combination of the effects of all these modes. But, in practice,... 

An injector is one of the most important components of the two components chemical propulsion system used in satellite control. The design of an injector is a complicated and time-consuming process and is largely dependent on laboratory data. In this study, the spray characteristics obtained from a small scale swirl injector under different operating conditions have been experimentally measured in a laboratory environment, such as the injector discharge coefficient, spray cone angle, and the distribution of droplets in the field. To calculate the discharge coefficient, the flow rate of the injector has been measured for different operating pressures. The shooting method and image processing... 

Performance of civil infrastructures, such as high-rise buildings, bridges, tunnels, offshore platforms and other structures may be critically influenced by existence of structural damages or even lead to devastating consequences. Structural Health Monitoring(SHM) and damage detection denotes the ability to monitor the performance of structure, detect and assess any damage at the earliest stage in order to reduce the life-cycle cost of structure and improve its reliability and safety. Generally, damage is defined as some changes in the physical properties of a structure, such as stiffness matrix. On the other hand, presence of damage causes changes in structural dynamic characteristics, such... 

Recognizing human actions is an important and challenging topic in computer vision, which has important applications such as video surveillance and Indexing. From a computational perspective, actions can be defined as three-dimensional patterns, in space and in time which can be modeled using several representations. Action representations differ in visual information used in spatial dimensions (e.g., shape or appearance) and the representation of dynamics in time. The goal of this thesis is to develop new techniques and improve current results in action categorization. As such, using a general structure, three methods are proposed. In this structure, local spatio-temporal features are... 

A flow for a graph or a combinatorial design is an element of the nullspace of its incidence matrix. For an integer r ≥ 2, an r-flow is a flow whose values belong to {±1;±2; : : : ;±(r - 1)} and for a real number r ≥ 2, a circular r-flow is a flow whose values are real numbers in the set [-(r- 1),-1]U[1, r - 1].In the context of undirected graphs, flows are called zero-sum flows. In the first part of this dissertation, we study circular zero-sum flows of graphs and prove a necessary and sufficient condition for the existence of a circular zero-sum r-flow in a graph in terms of its factors. Also, we investigate the minimum value of r for which a k-regular graph has a circular r-flow and... 

This thesis presents an extension of an analytical method previously introduced for evaluation of the deformation capacity of RC columns. The method utilizes fiber elements to arrive at nonlinear moment-curvature relationship for each segment. An existing stress-strain model has been modified and used in this study. This model considers the crushing failure of confined concrete, buckling of longitudinal reinforcements in compression, and their fracture in tension. It also accounts for the spiral fracture. This method was employed to determine the force-displacement diagrams for circular RC columns dominated by flexural mode of failure, and was calibrated against a number of relevant... 

Sometimes, the relationship between two random variables is not a correlation, but, a causal relationship where only changes in one of the two variables can lead to changes in the second one. The importance of examining such cause-effect relationships lies in the fact that sometimes, beyond just knowing the correlation between two variables, we are looking for an active effect on one, and knowing whether or not other correlated variables will also change with the change of this variable is of key importance. Such a process of exploring and analyzing cause-effect relationships is called causal learning. Based on this, in this thesis, we will first review the methods of causal inference, as... 

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... 

Up to now many different mechanisms have been proposed for a swimming micro robot, but most of the previously designed micro robots are not able to perform three- dimensional maneuver and the motion of the proposed swimmers are limited along a straight line or in a plane. Some important issues that must be ruled in designing micro robots include: reduced number of actuators, high maneuverability, high motion controllability and elimination of lateral drift. In this study the aim is to design a micro swimmer with the aforementioned capabilities as much as possible. In this regard, many different ideas based on the quadrotor motion, flagellated bacteria and spiral flagellated bacteria, Fish... 

Some have argued that two-way markets, such as the online rideshar-ing platforms, which divide their services into different segments and provides each of these segments to the independent workforce based on an articulate and transparent income criterion, are more attrac-tive to women, which in turn, can reduce income disparities. This is due to the flexibility in working hours as well as the transparency of the labor payment process. In this study, using micro-data related to the trips of male and female drivers of Tap30, we find out that there is a 2.2 % gender earning gap between drivers. Furthermore, the fac-tors affecting the possible income difference are identified. On the one hand,... 

Water plays an essential role in the daily lives of humans, plants, and animals. Due to the lack of safe water on the planet, in recent years there have been many challenges in the field of water treatment, which has made water desalination technology always one of the most advanced technologies. The most advanced technology in this field is the use of nanotechnology in water and wastewater treatment, especially the use of Membrane processes such as reverse osmosis. Unlike conventional reverse osmosis membranes, nanoporous membranes can ensure rapid water transfer during the displacement process. The purpose of this thesis is to introduce new monolayers that have an incredible performance in... 

In this study, three recent predictors of severity of coronary stenosis including fractional flow reserve (FFR), instantaneous wave free-ratio (iFR) and coronary flow reserve (CFR), are calculated for a number of patient-specific models of left coronary arteries. These patients are admitted to Tehran heart center. The main aim is presenting the optimum numerical and clinical detection technique to assess the severity of coronary stenosis. The effect of geometric features of stenosis is studied on the results of the FFR, iFR, and CFR in order to determine their accuracy. It is observed that CFR does not have a good estimate of the amount of disease. But, iFR, as a less risky test than FFR,...