Sharif Digital Repository

The heavy ion collision experiments are in progress in order to investigate how the Universe has evolved after the Big Bang. The recent observations show that a nearly perfect fluid is produced after heavy ion collisions. An appropriate incorporation of the relativistic hydrodynamics and the field theory would help us to describe the dynamics of QCD (Quantum Chromodynamics) matter under extreme conditions, and to survey the expected phase transitions. The majority of efforts to investigate the characteristics of the QCD plasma are devoted to an ideal, non-dissipative one. To get the results which are highly in accordance with the experiment, it is necessary to bring also in mind the role of... 

Throughout localization algorithms, sound source localization has received much interest using microphone array. Applications like tracking and determining angle of acoustic signal arrival have been combined with array processing techniques in the previous decade. Distributed micro sensor array have been suggested for a wide range of nowaday’s localization algorithms. The major goals are monitoring the environment, distinction, and pursue some phenomenon. This type of networks can be utilized for military application in tracking acoustic sources. Today’s advancement in technology allows implementation of the ultra low cost and low power integrated circuit for such application in the form of... 

In positioning and navigation, Sonar with utilization of sound waves in water environments is similar to the role of Radar in not watered (irrigated) environments. In the Sonar field, modeling and simulation of propagation of sound waves in the undersea environment is a fundamental and very important topic. Nowadays simulation is significant tool that allow to the researchers to predict the quality of Sonar function respect to the experimental conditions. For simulation and modeling of sound wave propagation are used two different methods; Wave theory and Ray theory. In the wave theory, because of the large volume of data, the interpretation of the results is hard. Also in this method cannot... 

Sound source localization has been one of the fundamental problems in many areas, including radar, teleconferencing or videoconferencing, localization of earthquake epicenters and underground explosions, microphone arrays, robots, etc. All of sound source localization ideas are like human auditory system. The human auditory system is a complex and organic information processing system. It can feel the intensity and spatial orientation and other information of sound. The distance of the two ears on our head is about 20cm. When the sound reaches each ear, there are small time difference, intensity difference and phase difference. After analyzing these differences by the brain, the human can... 

The ossicular chain of the human middle ear has a key role in sound conduction since it transfers vibrations from the tympanic membrane to the cochlea, connecting the outer and the inner part of the hearing organ. This study reports firstly a description of the main anatomical features of the middle ear to introduce a detailed survey of its biomechanics,focused on model development, with a collection of geometric, inertial and mechanical/material parameters. The joint issues are particularly discussed from the perspective of developing a model of the middle ear both explanatory and predictive. Such a survey underlines the remarkable dispersion of ... 

With advances in technology, production and propagation of sound waves in the air has become very important. One of the main goals of study of these waves is controlling them. The environment plays the most important role in sound propagation. Therefore, the properties of the environment and their effects should be studied. One such concern studied widespread previously, is porosity and porous media effects on the properties of a fluid flow and sound waves through it. An important application of this study is sound proofing systems. In this project two-dimensional numerical simulation of aeroacoustic waves passing through a porous media is carried out, using Lattice Boltzmann Method. The aim... 

Over the years, The robots have entered the human community in addition to the factories and industrial centers, and a new branch in the field of robotics called social robots has been created. Such robots can become a personal companion for children and elderly people who accompany that person at home or outside. Social robots can even be used as a platform for health services or as a vendor in stores. The interaction of humans and robots in social robots and communicating with the audience is the main part of this series of robots. Human-robot interaction can be divided into three parts: visual, auditory and facial or body movements. Also, the behavior of a social robot must be as natural... 

One of the most important noise produced by craft, is the propeller noise which must be identified and measured for many reasons, including military and engineering applications. Therefore, in the first step, the sources of noise emissions in the propeller are studied, and after describing the research background, the governing equations of this research are examined. Then, to validate, the DTMB 4119 propeller, which has hydrodynamic and hydroacoustic results, is used. In order to carry out the investigations, a B series propeller model is selected and compared with changing the parameters of the Rake, Skew, Pitch ratio and the number of blades for their hydrodynamic and hydroacoustic... 

The silencer is used to reduce sound in the vehicle, air conditioning channels, power plants and guns. Functional parameters of the sound amplifier are the amount of noise reduction and pressure drop. There are few studies on the flow and pressure distribution in the silencer, and there is no article about the effect of the size of the internal passages on the pressure drop and acoustical performance of the silencer. Few studies have been done on the effect of the absorbent fiber diameter on the acoustic performance of silencer. In this study, the effect of different shapes of internal channels (extended tubes, baffles and number of chambers) on the pressure drop and acoustic performance of... 

In drilling oil well with respect to depth of several thousand meters, knowing the physical conditions of down-hole well such as temperature, pressure and stress have particular importance in prevention of possible injuries such as breaking the drill bit or increasing temperature. If these data can transfer from down-hole to bore-hole of the well, the operators can prevent from critical conditions such as intertangle of the drill-string. Currently, because of this lack of information, there are irreparable damages in oil industry annually. Based on researches, because of down-hole conditions of the well, these data can’t transfer with electromagnetic telemetry. Currently one of the data... 

Troposphere layer includes complex flows which their effects in acoustic sensors are indicated as acoustic wave noise.It is essential to analyze these complex flows to recognize how to reduce the noise. In this thesis we have perused and modeled the sound wave propagation in troposphere layer.Given data are some thermal and velocity profiles of atmospheric flowsthe assumptions are: 1- gravity waves are negligible, 2- air density depends only on altitude, 3- sound waves parabolic equation assumptions are applied. Our goal Is to find the sound pressure level originated from a sound source in troposphere layer.This thesis emphasizes on analysis, recognition and modeling of the problem. Main... 

One of the most common methods for determining elastic moduli of rocks and porosity is acoustic velocity log. The elastic moduli of reservoir rock are widely used in geomechanical modelling, borehole stability and hydraulic fracture design. Carbonate oil reservoirs are known for heterogeneity and anisotropic nature. Therefore correlation of acoustic velocity and rock properties are generally challenging. Rock’s shear modulus is very important during saturating of sample with pore fluid because assumed it is independent of pore fluid type. However due to the several fluid-solid interaction mechanisms such as velocity dispersion, surface energy reduction and viscous coupling, shear modulus... 

In this study, a numerical investigation of propagation of sound through a fluid-saturated porous column has been proposed so that we can analyze the effects of porous media parameters on decreasing sound amplitude. The mathematical model applied for our simulation is based on Biot equations solved by an explicit finite difference method. Since Biot model is exclusively applicable to porous solids saturated with single fluid phase, in order to simulate a porous solid saturated with two immiscible fluids, we exploited the general Eulerian model instead of Biot model. Efficiency of porous sound absorbers is directly influenced by four major parameters which are porosity, rigidity and thickness... 

The impact of a method on the turbulence reduction in wind tunnels was evaluated. In this method, by installation of trip strip in the contraction, the unsteady behaviors of flow have controlled, consequently the turbulence intensity and possibility of separations were decreased. Location and diameter of trips were very important in this method. Various sizes of trip strip were installed at different locations in the contraction section of four different wind tunnels to study the most significant aspects of the method. Hot wire anemometry system, 1-D and 2-D probes, were used for turbulence measurement and a new method for direct calibration of a 2-D hot-wire probe was introduced. The new... 

“Motor Theory” of speech perception discusses the role of motor competence in speech perception. Motor  Competence  is  accessed,  simulating  the  gestures  which  lead  to  the  heard  voice  signals.  Simulating is done using mirror neurons which share similar feelings between sender and receiver. Empathy,  caused  by  usage  of  mirror  neurons,  probably  caused  some  sort  of  link  between  inward  motor gestures and outward semantic categories at the origin of language. Some degree of linkage between sound and meaning is what we call “Sound Symbolism”. Along  with  describing  the  link  between  Motor  Theory  and  Sound  Symbolism,  this  thesis  took  two  approaches to analyze... 

Tool Condition Monitoring (TCM) is a vital demand of advanced manufacturing in order to develop automated unmanned production. Tool condition has an essential influence on machined surface quality and dimension of manufactured parts. Continuing machining operation with a worn or damaged tool will result in damages to workpiece and even the machine tool itself. This problem becomes more important in supplementary machining processes like drilling in which the workpiece is usually at the final stages of production and any damage to workpiece at this stage is irreparable and results in high production losses. In this thesis, sound and vibrations signals are analyzed for drill wear detection.... 

Carbon Nanotube webs exhibit interesting properties when used as thermo-acoustic projectors. This work studies thermo-acoustic phenomena of these sound sources both in near and far field regions. Our three-dimensional simulation and experimental data show pressure waves are highly affected by dimensions of sound sources in near field due to interference effects. Although pressure amplitude increases with increasing frequencies, maximum pressure amplitude reached in lower frequencies may become larger than its maximum amount at higher frequencies because of interference effects. Measurement of different surface area sources shows generation of sound waves in far field is independent of... 

The application of acoustic waves as a diagnostic tool in medicine is highly regarded. Because of the mechanical and Noninvasive nature of this waves when penetrate in the body will not have any adverse effects on the body. Thus development and operation of these waves is growing every day. If abnormal changes in soft tissues (such as tumors inside the body) is created, by the reflected sound waves easily recognizable although it is experimental, and a little scientific studies have been conducted on the contrast of soft tissue and acoustic waves. Soft tissues of the human body Because of the asymmetric structure has a non-uniform physical and mechanical properties in different directions,... 

Carbon nanotubes have special thermodynamic properties which makes suitable as a thermo-acoustic sound source. Recently it is shown that by using these nanotubes it is possible to generate strog sound waves in air or water. Experimental analysis of phenomenon can be complicated and expensive. Hence this fact, in this study using molecular dynamic simulation, numerical analysis of sound generation with CNTs in air and water is discussed. For this purpose, the required structue of the system is generated and it has reaced equilibrium. This process has been done for 6 different CNT and for each CNT there are 5 different distances between them. Althogether, 30 different cases has is used for...