Sharif Digital Repository

This dissertation documents the study of Omni-max anchor, and the development of a computational procedure and its application to the analysis of OMNI-MAX anchor behavior under mooring loads. An OMNI-MAX anchor is an offshore anchor designed and developed in recent years, to overcome the uncertainty in the capacity of ordinary offshore anchors.In the process of this research to understand the capacity and mechanisms in which the anchor carries applied loads, the contribution of different parts of the anchor to the total capacity of the anchor is estimated using classical soil mechanics. Then, due to the failure of the used approach to model the dynamic behavior of the anchor and to better... 

One strategy for increasing efficiency and decreasing brake specific fuel consumption in spark ignition engines is using variable valve timing mechanism which is proportional to engine speed and load. Variable timing refers to the opening and closing time of inlet and outlet valves and their duration and overlap. In conventional SI engines the performance of valves is designed on a fixed point at special engine load and speed. While investigations show that if performance time of valves is changed according to engine load and speed, performance parameters of engine will improve.
In reviewing articles related to variable valve timing, their effect was considered on volumetric efficiency.... 

In this research, path planning in unknown environment is considered. It is assumed that the robot’s sensors are the only tools to collect information from the scene. Volume of the information gathered from the environment depends on the capability of the sensor. So, a detour from the optimal path is unavoidable. In this research, the basic robot is equipped with a minimal sensing system that only detects the iscontinuities in depth information (gaps). We present some online search strategies that guide such a robot to navigate unknown streets from a start point s to reach a target point t. Then, we empower the robot by adding a compass to patrol more general classes of polygons. We present... 

It is widely recognized today that excess moisture in pavement layers, when combined with heavy truck traffic and moisture-susceptible materials, can reduce the service life. Temperatures below freezing can also contribute to durability problems of saturated materials. A major objective in pavement design is to keep the base, subbase, subgrade, and other susceptible paving materials from becoming saturated or even being exposed to constant high moisture levels over time. The use of subsurface drainage has gained popularity over the past two decades, and many pavement agencies now routinely specify drainable pavement structures to reduce moisture-related problems in avements. In this... 

Early failure of pavement is one of the most important problems. As the research conclusions in Iran, Non-conformancity is the most important cause of this problem.Quality management system, Audits and expert systems are the solutions. This research provides an Audit system for quality management system of batch-type asphalt plants as the preliminary solution.A state survey conducted and useful part of state programs had been considered. After developing software, The system functionality has been tested  

This paper is concerned with the Vehicle Routing Problem (VRP) in a fleet with customer loyalty. In this work, we consider priority for customers according to their loyalty and try to declare an objective function which concerns customers' satisfaction along other normal VRP objectives like route optimization  

Asphalt concrete is a heterogeneous and multi-phase material that consists of aggregates, asphalt binder, and pores. These components create a complex microstructure. There is no consensus on how to quantify the microstructure and the required parameters from two-dimensional images. The load transfer can be managed by aggregate-aggregate or aggregate-mastic interactions that depend on the gradation, aggregate internal structure, and asphalt binder viscoelastic properties. The most important internal structure indices affecting the behavior of HMA are aggregate orientation, contact orientation, contact length, and number of contact points. In this research, the influence of aggregate... 

The theory of nonlocal gravity is a classical modification of Einstein’s general relativity, that explores nonlocal effects of gravity by putting aside the locality postulate, or the assumption that the non-inertial observer is equivalent to an inertial observer with the same speed at each instant of time. In this research we explore the local limit of this theory, or in other words, we consider nonlocality with only a short-term memory, with the goal of calculating the effects of nonlocality on cosmology in mind. We calculate these effects that are formulated inspired by the effects of materials in electrodynamics, on a homogenous universe in the local limit. We also reproduce the theory of... 

Dead Reckoning navigation, as an infrastructure-independent approach, plays a key role in scenarios where access to the Global Navigation Satellite System (GNSS) is unavailable; however, its performance is consistently affected by the accumulation of errors in inertial measurement unit (IMU) sensors. In this research, a novel approach is proposed to enhance the accuracy of this method. In the first stage, sensor noise modeling is performed using three innovative approaches. The first approach involves a static tuning based on an adaptive Extended Kalman Filter (AEKF). In this method, the discrete process noise covariance matrix is adaptively estimated, and the continuous-time process noise... 

Pipe freezing has become well established in industry as a method of short-termisolation in order to carry out maintenance or repairs. It is often necessary to repair system components without plant shutdown or drainage of system having many piping structures which may have hazardous or expensive fluid. Therefore, a series of tests has been arranged to investigate the ice plug formation in two standard pipes with different diameter size. The freeze zone on the pipe has been created by means of an aluminum jacket which liquid nitrogen flows in it. In the tests the freezing time, amount of liquid nitrogen usage andthe pressure tolerance of ice plug have been determined. Moreover, the numerical... 

In recent years, the area of research on micro flying robots has been developed due to the development in micro manufacturing technologies. Due to extra advantages of these flying robots, they are implemented in military and civilian missions such as identifying, espionage, aerial relays, traffic surveillance, rescue, aid, etc. Ability to fly in specified areas, without human injuries, low manufacturing and energy costs, easy and fast implementation, Easy Maintenance, etc, which are some advantages of these robots. We can control these robots manually by remote controllers (RC) or by Auto guidance systems. On the other hand, these robots are used in research laboratories for testing new... 

Range Profile (RP) is known as one of the most important tools for radar target recognition. The main problem with range profile for radar target recognition is its sensitivity to aspect angle. To overcome this problem, range profiles are assumed to have the same statistical characteristics in small frames of aspect angles or context dependent models such as HMM may be used. All methods presented, seems to have some shortcomings to offer a model based on physical circumstances of target maneuver. For example in such models, consecutive samples of RPs in an aspect frame are assumed to be statistically independent with the same distribution (IID). Here we propose dynamic system (DS) for... 

The present thesis aims at investigating the dynamic interaction of slosh and aeroelasticity in the fuel contained aero vehicles. The main approach in this research is to develop reduced order models for description of the coupled system. In this regard, boundary element method is used to develop slosh dynamic model. Axisymmetric boundary element method with non-symmetric boundary conditions is used to develop slosh dynamic model for axisymmetric containers. Zoning method is used to develop slosh dynamic model for the multi-baffled tanks and based on it, slosh equivalent mechanical model is developed for multi-baffled tanks. Finite element method along with modal technique is used to develop... 

There are numerous ways available to achieve low temperatures that cryocoolers might be among the most important of them. In the meantime, the pulse tube refrigerator has a special place due to its simple geometry and not be using any moving parts. This simple property make the pulse tube refrigerator one of the most popular methods to achieve low temperatures. Nowadays, a pulse tube refrigerator is used for cooling in the range of 4 to 123 Kelvin in two form of one-stage and two-stage and up to an approximate power of 1 KW. Today, due to the temperature and the amount of power required for cooling, as well as the time it takes to reach that temperature, this chiller is used in medical,... 

During the last few years, the study of urban environment structures is considered as a research field of interest in remote sensing. In satellite observations of the earth's surface, continuous imaging in terms of time and space has caused the remote sensing technique to be proposed as a useful and efficient tool for the analysis of urban areas. Obtaining quantitative spatial information from the urban environment in fields such as determining the height of buildings plays an essential role in urban planning, monitoring damage to buildings, establishing communication bases and digital cities. During the last two decades, the use of Tomosar approach in order to reconstruct the structures of... 

In synthetic aperture radar (SAR) satellites, the nadir echo is defined as the backscattered signal from the point directly below the satellite on the earth surface. If the timing of the radar is such that the nadir echo arrives at the receiver while the receiver is turned on for receiving the desired signal, it could damage the receiver or disrupt the resulting SAR image, unless it is suppressed enough by proper design of antenna radiation pattern. In current SAR satellites, ”avoiding” this phenomenon is associated with two problems: 1) limiting the swath width, 2) imposing stringent restrictions on the selection of pulse repeatition frequency (PRF). Therefore, ”suppressing” the nadir echo,... 

Localization of radio sources has various applications in civil and military communications. Some of important localization methods consist of Angle of Arrival (AoA) estimation of the illuminated signals from the interested sources. Between various Direction Finding (DF) methods, subspace based methods are of special importance, because of their high resolution and accuracy. And from beginning of invention, because of new challenges, have been focus of numerous researches. In this thesis, first we explain the most important subspace based DF methods called MUSIC and root-MUSIC. Then a novel modification for root-MUSIC is introduced. In our new method the computational complexity of...