Sharif Digital Repository

Supersonic separators (3Ss) are used in gas separation processes such as dehumidification of humid air thanks to their high performance and good pressure recovery. Moreover, 3Ss because of their simple mechanical construction and absence of any environmental impact are preferred to other dehydration methods of natural gas, such as adsorption, cooling, and membrane. Also using the 3Ss for relatively large facilities with considerable investment is more than evident. In the first phase of present study, 2-D simulation is performed to investigate the effect of operational and thermo-physical parameters on shockwave position in a specially conceived wet air 3S. Moreover, the effect of cyclonic... 

In this thesis, localization of a postulated noise from limited neutron detectors sparsely distributed throughout the core of a typical VVER-1000 reactor is investigated. For this purpose, developing a 2-D neutron noise simulator for hexagonal geometries based on the 2-group diffusion approximation, the reactor dynamic transfer function is calculated. The box-scheme finite difference method is first developed for hexagonal geometries, to be used for spatial discretisation of both 2-D 2-group static and noise diffusion equations. Using the discretised static equations, a 2-D 2-group static simulator (HEXDIF-2) is developed which its results are benchmarked against the well-known CITATION... 

Abstract The problem of competetive facility location can be defined as follows: There are a number of customers in the form of points in space, and two players arrange a number of facilities in the form of points in space, given some limitations, respectively. Each customer’s connection to each facility has a cost for the customer and an advantage for the facility, and each customer wants to be connected to at most one of the facilities which has the lowest cost for him. The goal is to find the strategy of placing the facilities and determining the cost which the facility receives from the customer, in such a way that the player’s profit is maximised.In this thesis, we first sought to... 

The unique ability of additive manufacturing in manufacturing industrial parts with complex geometries has led to the development of topology optimization methods and their use for the optimal design of parts in various industries. However, considering the limitations of additive manufacturing methods in the optimal design of parts is usually a difficult process, and when making decisions, facing multiple conflicting design goals is often difficult and usually involves high computational cost. The main goal of this research is to provide a topology optimization method for generative design for additive manufacturing based on the concept of constructive solid geometry and using machine... 

Multi-part rotating parts are used in various industries with very high revolutions. Therefore, the method of assembling each part and keeping the axis of rotation of each part close to the axis passing through two supports (bearings) is important. In this research, three main steps are followed, the development of the differential equations governing the multi-part rotating system and the calculation of the range of oscillations created at the critical points, and then the calculation of the optimal assembly angles with the aim of reducing the introduced oscillations, and finally the discussion of crossing the speeds A crisis is being investigated. The method of obtaining the system of... 

Some types of composite material used in aerospace industry make with braiding technology and Some type of fabric textilled with braiding machine, one of them is 2-D Triaxial braid fabrics.In this thesis, generated new an analytical model for predicted mechanical properties of 2-D Triaxial braid composites. This can prediceted equal elastic modulus and equal shear modulus and equal passion ratio for this composites and this model can predicetd volume fraction of fibers and resin  

Future generation ships will be powered by highly efficient contra rotating propellers propulsion systems. The research presented in this thesis leads to a thorough understanding of Contra Rotating Propellers performance.At first tow propeller was detected. The propellers was drawing in Catia and simulated in Ansys Fluent.Also the propellers hydrodynamic forces was available in DTMB cavitation tunnel. Also a model of propellers was tested in Sharif University of Technology cavitation tunnel. Experimental results were obtained for the forces and torques on the propellers over a range of advanced coefficient. The velocities were measured in the field in near the propellers.The results of... 

In the behavior of many convex optimization problems with random constraints in high dimensions, sudden changes or phase transitions have been observed in terms of the number of constraints. A well-known example of this is the problem of reconstructing a thin vector or a low-order matrix based on a number of random linear observations. In both cases, methods based on convex optimization have been developed, observed, and proved that when the number of observations from a certain threshold becomes more (less), the answer to the problem with a probability of close to one (zero) is correct and the original matrix is reconstructed. Recently, results have been obtained that explain why this... 

The kidney is one of the most complicated organs in terms of structure and physiology, in part because it is highly vascularized. Previous investigations have focused on specific characteristics like length and diameter. There are a few methods like those which are based on image processing techniques, that have been focused on all features as a unique structure. The clear drawback of these approaches is inability to justify growth and changes. Lindenmayer system (L-system) is parallel rewriting method and a type of graph grammars. L-system can justify growth and all characteristic changes and adopt itself to them. Parametric rewriting rules incorporating within physiological laws of the... 

The visibility graph of a simple polygon represents visibility relations between its vertices. Since each vertex in a polygon is visible from the two vertices adjacent to it on the boundary of the polygon, this boundary is analogous to a Hamiltonian cycle in the visibility graph of the polygon. Therefore, visibility graphs are Hamiltonian. Finding this Hamiltonian cycle can be of great help when solving visibility graph recognition problems, in which one should decide whether a given graph is a visibility graph of a simple polygon; and reconstruction problems, which include constructing the polygon corresponding to a given visibility graph. These problems have been solved for the special... 

A basic technique in data reduction is to approximate a collection of data by another collection of smaller size. Then, the resulted data are easier to be processed or maintained. An example of such large scale data is the ordered sequence of n points describing a path or a region boundary. We are given a sequence of points p , p , ..., p , and we consider the 1 2 n problem of approximating these points by a path with k < n line segments which error of this path is not greater than special value. Various criterions are defined to compute the path simplification error.This problem can be used in GIS, Image Processing and Computer Graphics problems. In this thesis, we consider special case... 

Planar visibility computing is defined as determining the region of the plane that is visible from a specific observer. This concept has many applications in computer graphics, robotic and computer games. In this thesis we consider two visibility problems: the visibility testing problem which checks the inter-visibility of two objects and the visibility counting problem which counts the number of visible objects from an observer. For these problems we propose new algorithms which have some improvements compare to the previous ones  

Planar visibility computing is defned as determining the region of the plane that is visible from a specifc observer. This concept has many applications in computer graphics, robotic and computer games. In certain visibility problems, counting the number of visible objects in an appropriate time is required. For obtaining a solution fast, current algorithms give an approximated count. In this thesis, we consider visibility testing problem and visibility counting problem.For a given set S = fs1; s2; :::; sng of non-intersecting segments and a query point p in the plane, the visibility testing problem checks the inter-visibility of p and a segment si 2 S and the visibility counting problem... 

Motion is an impartible component of our physical environment and the most obvious consequence of motion is collision. Diverse applications of collision detection algorithms in various real world simulated environments have led to numerous solutions to this problem from different aspects of computer science. Within computational geometry, kinetic data structure is the well-known framework to detect collisions of moving objects.This thesis will look into the problem of collision detection for a number of disjoint disks moving freely in 2D plane. To this end, we will provide a kinetic data structure (KDS) that uses O(n) storage and under the assumption of pseudo algebraic motion plans,... 

This thesis is devoted to study some asymptotic behaviors of Poisson Voronoi tessellation in the Euclidean space as dimension of the space tends to infinity. First we use Blaschke-Petkantschin formula to prove that the variance of volume of the typical cell tends to zero exponentially in dimension. It is also shown that the volume of intersection of the typical cell with the co-centered ball of volume converges in distribution to the constant . Next we consider the linear contact distribution function of the Poisson Voronoi tessellation and compute the limit when dimension goes to infinity. As a byproduct, the chord length distribution and the geometric covariogram of the typical cell are... 

Wireless communication networks are undergoing a significant transformation from coverage-driven deployment of macrocells to user-centric and cluster-based capacity-driven deployments of low-power base stations (BSs), usually at the locations of high user density. On the other hand, the increasing irregularity and randomness in the locations of nodes has led to an increased interest in the use of random spatial models along with tools from stochastic geometry and point process theory for their accurate modeling and tractable analysis. To this end, this thesis investigates clustered networks for different wireless applications. In this regards, comprehensive and tractable analytic frameworks... 

With rapid increase of availability of moving object data, especially with help of GPS, need for algorithms which can process spatiotemporal data and data structures capable of storing it efficiently, has been increased. One of spatiotemporal data applications is in wild life, which demands tracking of animal movements through time. One of problems introduced in this application is flock problem. Flock is a group of entities, which move together through time. There is a belief that in bulky data, there are a lot of hidden information and patterns. Hence, we believe that with help of flocks, we can get insight of animal behaviors in environment and to each other. In this thesis we will... 

We design a new algorithm for clustering data streams in any fixed di- mension, that use the framework of core-set to summarize data, in order to reduce the complexity of computation. Clustering is to separate data into distinct sets called clusters, which objects in the same cluster has the most similarity and objects in the different clusters has the least similarity.This problem has many application in the areas such as: machine learning,image processing, financial and stock transactions. Data stream has recently emerged as an important concept because in many applications, data is inherently streaming over a network or the data base is extremely large and sequential access is way faster... 

The Very-High Temperature Reactor (VHTR) design is one of the six candidates for the Generation IV nuclear reactors. The reactor core type of the VHTR design is either prismatic or pebble-bed. In pebble bed reactors, the core is filled of thousands of graphite and fuel pebbles. Fuel pebbles in these reactors consist of TRISO particles, which are embedded in a graphite matrix stochastically. The reactor core is also stochastically filled up of fuel and dummy pebbles with an unequal ratio. These two stochastic geometries are the so-called double heterogeneous of this type of reactors. In the current study, a... 

Moving data is becoming more and more important in different areas such as air traffic control, mobile communications, geographical information systems, GPS and other advanced technologies. In most cases, the path trajectory of such moving data is not known in advance. Moreover, they can change the direction and their speed of motion. Recently, a moving model, called black box model, has been proposed for such environments. In this model, there is a sequence of time stamps in which the position of each object is reported and the maximum displacement of each object in a time step is bounded by a known constant, dmax. In this thesis, we use this model to solve some computational...