Sharif Digital Repository

Atherosclerosis is a vascular disorder caused by inflammation of the arterial wall. This inflammation leads to the accumulations of low-density lipoprotein (LDL) cholesterol, monocytes, macrophages and fat-laden foam cells at the site of inflammation, often referred to as plaque formation. This work uses a mathematical model for simulating the deposition of atheroma plaque in coronary arteries. In this study, the effect of time average wall shear stress (TAWSS), oscillatory shear index (OSI), non-Newtonian characteristics of blood and variable hematocrit values on the occurrence of atherosclerosis in a three-dimensional coronary artery was numerically investigated. Simulations was conducted... 

Blood clotting and clot formation in damaged vessels are vital mechanisms of the body. Any disorder in performing this mechanism leads to various problems such as excessive bleeding or, on the contrary, causes vascular occlusion and diseases such as embolism. Due to the importance of this issue, extensive research has been done to understand this phenomenon and the factors affecting it. In this thesis, the effect of shear stress, coagulation factor concentration and wound location in coronary bifurcation on clot formation and growth and its interaction with velocity field is numerically investigated. Blood flow is modeled non-Newtonian with Carreau-Yasuda model. Various chemical species... 

Carotid bifurcation is one of the most important bifurcations in human body which has a lot of curvature in some people. The common carotid artery bifurcates into an internal carotid artery (ICA) and an external carotid artery (ECA). The incidence of stenosis in carotid bifurcation and in particular in the internal carotid artery is of special importance. In the United States of America by 2006, nearly 700000 strokes occur each year, with about 160000 deaths and 20 to 30% of strokes are caused by stenotic carotid that cost estimated at $160 billion. The purpose of this thesis is to investigate in hemodynamic factors of blood flow such as velocity variation, vortex patterns, shear stress and... 

When a fluid moves inside another fluid while they have unequal density, a phenomena occurs which is called density (or gravity) current. Therefore density difference and gravity are key factors of density current generation. Due to application in engineering and geology, it is essential to investigate and analyze the above mentioned phenomena. Dam reservoirs, sandstorm in deserts, snow slide onset and falling, ash clouds produced during eruption of a volcano, and spreading of density current due to the collapsing of reservoirs are some examples of gravity current. There are lots of methods to simulate the turbulence of density current like DNS or RANS. But DNS has high computational cost... 

Density currents, caused by the intrusion of dense fluids under lighter ambient fluids, frequently occur in both natural and industrial situations. As a result of the density differences, the driving force can arise from soluble substances, temperature differences, etc. If the driving force comes from suspended particles including silt and mud, the currents are called turbidity currents. Due to the variation in concentration and the consequent driving force along the flow path, turbidity currents are significantly more complicated than saline currents. These currents play the most important role in sedimentation in lakes, seas and oceans. In addition, turbidity currents are the main factor... 

Turbidity currents are one of the more frequently observed types of stratified flows. In these currents, the density difference is created as a result of particles. Hydrodynamic instabilities at the interface of these currents could occur in various modes and have an important role in the mixing process. The main goal of this study is to investigate the interfacial stability of turbidity current, theoretical and experimentally. The linear stability analysis in temporal and spatial framework are used for studying the stability characteristics of a particle-laden stratified two-layer flow for two different background density profiles: smooth (hyperbolic tangent) and piecewise linear. The... 

In the present study, we are to investigate and calculate the drag coefficient in the secondary bag breakup regime in droplet experiment in which the liquid droplet falls into continuous air jet flow. A high speed camera is hired to record the pictures of this process. With the help of image processing techniques, parameters such as dimensionless diameter, growth of droplet, drag coefficient and etc. in secondary bag breakup regime are investigated. The liquid used in this experiments are water, gasoline and diesel fuel. Dimensionless number influencing the result of the experiment are weber and Ohnesorge numbers, with weber number ranging from 6.86 to 20.31 and Ohnesorge number ranging from... 

In the present study, hydrodynamics and particle sedimentation of a rectangular basin is studied numerically. Results are also validated with experimental data. Two major goals are perused in this work: First comparing LES and RNG k-ϵ turbulence models and second, investigating the accuracy of simulation of particle sedimentation by solving the concentration formula.
In order to achieve these goals, a 2D sedimentation tank is simulated using the RNG k-ϵ model. Velocity and concentration profiles are also plotted. Comparing the results with experimental data reveals that simulating sedimentation by the mentioned method has acceptable accuracy and can be used to predict sedimentation. In... 

Drop deformation and breakup are of great importance in a wide variety of applications, from fuel combustion to agriculture, pharmaceutical processes, and coating. In this experimental study, droplet secondary bag breakup has been investigated. By conducting experiments on different fluids with a wide range of properties and in different conditions, the effects of different parameters on secondary bag breakup have been addressed. For this purpose, the breakup of these fluids, water, ethanol, glycerin, and SDS solution were scrutinized and by comparing their trajectory and morphological parameters, results are driven. Experimental conditions were such that the Weber number are from 11 to 17... 

Bubble growth and formation is used in many of the two-component processes including gas and liquid such as extracting pure metal from ore, separation of water from oil, distillation and absorption. The regime of bubble formation determines the main characteristics of the mentioned process like bubble shape and volume, its formation time and the interaction of the successive bubbles such as collision or coalescence. So predicting the regime of bubble formation and its characteristics helps the engineers to control the process. In this presented research, through doing experiments, different regimes of air bubble formation in water and Aqueous glycerol i.e. single, double, multiplex and... 

In this study, DREAM model operation as a model to predict the occurrence of dust storms has been completed. The aim of this study is to identify capability of the model to predict dust storms in IRAN. The model has been run for June 2014 because on 2 June 2014, Tehran visited a dust storm with a speed of 111 kilometers per hour and yielded a huge economic losse. In this model, dust concentration,dust load and Aerosol Optical Depth(AOD) are calculated on an hourly basis. The model results do not captured the direct relationship between the average wind speed and dust Parameters and the model do not predict the dust storm on on 2 June 2014 in Tehran. The reason is that DREAM gets... 

Drop formation from the tip of a nozzle and its motion in bulk fluid is an interesting and practical process which has widely turned researchers’ attention. Investigation into the governing physics and effective parameters on formation, deformation and motion of a drop increases the efficiency of the related industrial processes. Thus in the present study, in order to simulate this process, full Navier-Stokes equations solved by the Volume of Fluid (VOF) method in an axisymmetric domain using Fluent software as the solver. In this research, the effects of Weber number (the proportion of inertial force to surface tension force) and Ohnesorge number (which refers to the proportion of viscous... 

Turbidity currents are produced when a particle laden fluid flows under the lighter ambient fresh fluid. The streaming of particle laden fluid is called turbidity current and this kind of currents is the major mechanism for sediment transportations in lakes and oceans. In the present research, the main concentration is on the effect of obstacle on the behavior of turbidity current. A series of laboratory experiments were carried out with various obstacle heights, shapes and different inlet densimetric Froude numbers. In each experiment, velocity profiles upstream and downstream of the obstacle were measured, using an ADV (Acoustic Doppler Velocimeter). Kaolin was used as the suspended... 

Wide and varied aspects of droplet motion due to its increasing application in various fields has attracted much attention. Analysis of mass transfer from the liquid drop into the other fluid, such as complex and intriguing problems in fluid mechanics, which is very important. Many experimental and numerical studies have been carried out in this case that the evelopment of laboratory equipment and software, are rapidly growing.
In this study, given the importance of this issue, experimental study on mass transfer in fluid systems solution droplet liquid - liquid extraction, have been considered. Different methods have been discussed to date. In the present study, using image processing... 

Gravity currents are a general class of flows in which the density difference between two fluids drives the flow. Turbidity currents are gravity currents in which the density difference is due to suspended sediment. Reservoir sedimentation is mainly occurs because of sediment transport by these currents. If turbidity currents can be stopped in a reservoir, or influenced in such a way that the sediments are not deposited in critical locations like bottom outlets, the storage capacity of the reservoirs can be increased considerably. In order to do this, various methods such as placing an obstacle in the path of these flows have been proposed. In this study, the effect of inlet sediment... 

In recent years, the increase of particulate matter concentration due to frequent dust storms has become one of the most important dilemmas of people around the world. The high concentration of dust particles causes irreparable respiratory diseases, premature death, economic and social damages. Because of placement in the vicinity of the main sources of dust, Iran has been severely affected by the phenomenon of dust storms and damage caused by it.In this research, two dust storms occurred in Tehran are simulated using WRF-Chem and HYSPLIT models. The first event took place on February 2, 2016, and the second event took place on May 22, 2018. In order to determine the empirical parameters of... 

Sedimentation tanks are one of the important and costly stages of water treatment process in which remained particles from previous stages settle down due to gravity force. In this research, the hydrodynamics of secondary settling tanks without and in the presence of particles is numerically investigated using VOF method in order to simulate the interphase using RNG k-ε for turbulence modelling. The simulations are performed by means of open-source code OpenFoam, and the code is developed to model particles in the flow. The calculated velocity profiles using VOF method show a reasonable agreement with the experimental data. Comparing the concentration profiles with experiments shows the... 

In this research, the characteristics of non-Newtonian, shear-thinning drop formation containing surfactant from a needle are investigated experimentally. The ambient fluid is air and all experiments have been conducted in a constant flow rate of drop phase fluid. Images of forming drop are taken using a high-speed camera and by processing them, important parameters in drop formation such as length of drop, minimum neck thickness, formation time and the size of satellite drops have been studied. Three non-Newtonian and three Newtonian fluids are considered in a way that the initial viscosity of non-Newtonian fluids would be equal to the viscosity of their corresponding Newtonian fluids.... 

Heart attack is considered as one of the most common reasons of morality all over the world. Coronary Atherosclerosis is known as the major causes of heart attack. The commence and proceed of this disease is related to cross of Low Density Lipoprotein. In this project, based on numerical simulation using ANSYS Fluent, hemodynamic variables and the rate of LDL particles penetration to porous wall of coronary artery is investgated. The geometry is the first bifurcation of Left Anterior Descending and is located on the supposed sphere that represents heart configuration. Sinsuidal variations of shere radii, simulates pulsating movement of heart. Heart diameter is supposed to remain constant... 

Due to increased atherosclerosis-caused mortality, identification of its genesis and development is of great importance. Although, key factors of the origin of the disease is still unknown, it is widely believed that cholesterol particle penetration and accumulation in arterial wall is mainly responsible for further wall thickening and decreased rate of blood flow during a gradual progression. To date, various effective components are recognized whose simultaneous consideration would lead to a more accurate approximation of Low Density Lipoprotein (LDL) distribution within the wall. In this research, a multilayer Fluid-Structure Interaction (FSI) model is studied to simulate the penetration...