Sharif Digital Repository

A popular way for performing minimally invasive heart surgery is to use cardiac stabilizers that fix the heart during surgery. In the recent years several research works have been conducted to develop effective cardiac stabilizers. While these developments have attempted to improve fixation of the heart, there are reports indicating that a rigid cardiac stabilization may induce injury to heart muscle tissues due to restricting the heart motion in all directions. A more efficient approach than rigid cardiac stabilization might be to use a flexible cardiac stabilizer in combination with a surgical robot having motion compensation capability. The scope of this research is designing a device to... 

Science has been improved in all aspects and robotics is considered an important field, which helps, do work more efficiently. In the meantime, one of the most popular aspects of robotics is the movement, both physical (in terms of the number of mechanical actuators, the number of arms and legs, the number of wheels, the robot's weight and gravity) and in terms of programming and algorithms. Programming and algorithms are divided into two categories: 1. Programs to control robots and manipulate dynamics associated with robot movement. 2. Algorithms and the ways for routing. The first group is programming associated with control of robots. Motion planning or path planning is the next. In... 

On the average, ten thousand people die annually due to earthquakes. A UNESCO study gives damage losses amounting to ten billion dollars within the years 1926 to 1950 from earthquakes. These data shows the importance of earthquake issue that causes the scientists to pay special attention to this subject. In despite of significant improvements in many of scientific fields, earthquake is still remains as an unknown event without the possibility of predicting its time and location of occurrence. Because of that, a large effort has been paid for rehabilitation of structures to prevent the human loss and maintaining the necessary life safety. In this regard, various guidelines have been proposed... 

Continuous improvement of the existing seismic design codes and regulations clearly shows the need for evaluation and probable retrofitting of the existing building structures. A large amount of literature has been produced on different topics related to retrofitting including FEMA 273, ATC 40, FEMA356 and most recently the draft of FEMA 440. On the other hand, it has been long recognized that the response of buildings to strong ground shaking caused by earthquakes results in inelastic behavior. Until recently, most structural analysis techniques devised for practical application relied on linear procedures to predict the seismic response of the building structures. But due to various... 

This thesis presented a state-of-the-art algorithm for perspective projection reconstruction of non-rigid surfaces from single-view and realistic videos. Which overcomes the limitations arising from the usage of orthographic camera model and the complexity and non-linearity issues of perspective projection equation. Unlike traditional non-rigid structure-from-motion (NRSfM) methods, which have been studied only on synthetic datasets and controlled lab environments that require some prior constraints (such as manually segmented objects, limited rotations and occlusions, and full-length trajectories); the proposed method can be used in realistic video sequences. In addition, contrary to... 

In this study the predictive power of “Simple Moving Average” simulation for three month horizon is investigated. The purpose of the study is expressed in two hypotheses. The first hypothesis is that there is a significant difference in the prediction of stock price volatility by “Simple Moving Average” simulation with the “Weighted Moving Average” model prediction and the second hypothesis states that using “Weighted Moving Average” model we can forecast volatility stock price for the out-of-sample period. The research data includes a series of total stock price indices from 2013 to 2018 extracted from Tehran Stock Exchange (TSE). For “Weighted Moving Average” model, three normal... 

In the present thesis, the movement of the clusters of fullerenes and nanocars are separately investigated on graphene surface, using molecular dynamics simulations. Investigating the fullerene clusters with different populations, it is concluded that, as the number of molecules inside the cluster increases, the displacement range of the motion decreases. In fact, some parts of the energy of the fullerene cluster are wasted through the intermolecular interactions, and as a result, the mobility of the cluster diminishes. During the investigation of the three-dimensional structures of fullerene, the wetting property of the clusters is revealed relative to the graphene surface. The decrease of... 

Purpose of this thesis is to discover the governing equation of Flying Wing aircrafts. In Flying Wing aircrafts crew, payload, fuel, and equipment are typically housed inside the main wing structure. A clean flying wing is sometimes presented as theoretically the most aerodynamically efficient (lowest drag) design configuration for a fixed wing aircraft. We assume Flying wing as plate. Achieve structural formulation needs to use modal deflections and put them in Lagrangian equations. In the right had side, pressure on flying wing can be found. To obtain air pressure on flying wing in this thesis, applying Quasi steady aerodynamic and Howe distribution is necessary. Applying this method on ... 

Understanding the physics of unsteady flow is very important due to various applications. Axial compressors, turbines, helicopter blades, and energy harvesters are the essential applications of this problem. An airfoil under pitching oscillation is one of the common cases in unsteady aerodynamics, and several characteristics of the flow around it have been investigated up to now. The frequency analysis of the wake flow for pitching airfoils has received less attention. In this research, experimental tests have been carried out for symmetric airfoil NACA 0012 under pitching oscillation in low Reynolds flow (6×104) and before the airfoil stall condition. The experiments were carried out in the... 

Space debris have increasing importance for space missions. The towing removal scheme is one of the most promising ways for active removal of these debris from LEO orbits. In this approach, an active propelled satellite captures the debris via a space tether and a tethered net which by producing a force opposite to its velocity, it will cause deorbiting and burning the debris in the dense atmosphere. One of the issues with this technique is the danger of tether rupture which for solving that two tethers instead of one can be used. In this research study of active removal of flexible space debris via double tethered towing system has been done. Dynamic modeling has been done with Newton’s and... 

Mono-copter has been considered as a type of drone in recent years. The initial idea for this micro vehicle was to follow the maple seed's motion as it fell from the tree. In this study, using dynamic modeling principles and with the help of aerodynamic relationships of non-permanent blade element as well as momentum theory, we present a dynamic model of forces and moments on this monocopter. Subsequently, using the Newton-Euler approach, the six-degree-of-freedom equations of motion of this are also developed and various simulations are performed on the model using software provided by Simulink Toolkit, which demonstrates the accuracy of the simulation. In addition, we obtain the different... 

The purpose of the present study is to model and control a 6DOF satellite dynamics with a rigid body in the Earth’s orbit including the fuel slosh. The satellite manages and controls its attitude and position by twelve ON-OFF thrusters installed alongside the principal body axes. Moreover, due to using the liquid fuel to feed these thrusters, fuel slosh may have a strong dynamical effect on the satellite translational and rotational dynamics and control. The thrusters’ activation may result in fuel slosh and the impact of their frequent switching ON-OFF on fuel is considered in this study. The thrusters force magnitude, switching intervals, and their frequencies can affect the magnitude of... 

In recent years, renewable energy equipments such as wind turbines has become more common for electric power generation. Due to the complexity of the aerodynamics of wind turbines,experimental studies in this field are very important. The purpose of this study is to investigate the aerodynamic performance of a new wind turbine airfoil in static mode and pitching motion.The airfoil is a section of 2 MW wind turbine blade, pitching around its quarter-chord axis .All experiments are carried out in a subsonic wind tunnel. In these experiments, the reynolds number is 140,000 and the reduced frequency varies from 0.034 to 0.126. Pressure transducers have been used to determine the pressure... 

The purpose of this thesis is to present a novel approach in Terrain Following/Terrain Avoidance (TF/TA) flight using Fuzzy Logic. The fuzzy logic can decide where and how the aircraft needs to change its altitude and/or heading angle. The method due to its fast decision making algorithms would be useful for on-line operation. It could also help design trajectories in an off-line manner. To achieve the above goal, the method effectively incorporates the dynamics of the aircraft and could handle tough terrains in terms of shape and peculiarities. The mathematical method basically, uses a special relationship among existing slope and slope derivative of the terrain together with aircraft... 

Dynamic analysis of deploying elastic arms of spacecrafts carrying tip mass has been presented. The research concentrates on the precise analytical simulation to reveal the phenomena which are usually eliminated in estimations. One of the most important factors which affect the dynamic response of such arms is rigid body dynamics of spacecraft. Considering this aspect of the problem the evolutionary analytical simulation has been developed through three steps. The first step focuses on the minute simulation of the arm deployment, in which a new mathematical approach called "elastic profile" has been developed which leads to semi-analytical solutions for the arm carrying tip mass.... 

In line with advances in science and technology in the areas of robotics, artificial intelligence, computer and control, unmanned vehicles are being more utilized and focused. On the other hand, development and further advances of these vehicles is highly dependent on the level of their autonomy. Motion planning is one of the most important issues in this regard. Due to high levels of autonomy required for unmanned air vehicles (UAV), the subject of motion planning is of valuable interest in aerospace applications. The goal of the motion planning problem, that is the subject of this research, is to extract an optimal trajectory for the UAV from an initial location toward its target point... 

This research is dedicated to specific issues in the field of Aerial Vision Based Navigation (VBN). It focuses mainly on vehicles with no pilot such as RPVs and small aircraft; having in mind their safety which must be close to commercial applications. Various methods have been studied and the simplest one; which is based on observation, identification and utilization of landmarks is selected for detailed implementation. In this work, we concentrate on using a single-camera while flying in an unknown environment (MonoSLAM). Other available sensors are accelerometer and GPS receiver to keep the cost down. Different studies show that using a low-cost single camera system is much more efficient...